MultiMode SPM Instruction Manual NanoScope Software Version 5 004-210-000 004-210-100 Copyright © [1996, 1997, 2004] Veeco Instruments Inc. All rights reserved. Document Revision History: MultiMode SPM Instruction Manual Revision Date Section(s) Affected Reference B 3-09-04 All. N/A 4.31ce “A” 27OCT97 Chapters 3, 5 and 8 168, 185, 189 4.22ce 14FEB97 TOC, TOW, Chapters 2, 5, 7, 11, 12, 13, 15 and Index 139 4.22 15JUL96 Released 8 Approval C.
Notices: The information in this document is subject to change without notice. NO WARRANTY OF ANY KIND IS MADE WITH REGARD TO THIS MATERIAL, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. No liability is assumed for errors contained herein or for incidental or consequential damages in connection with the furnishing, performance, or use of this material. This document contains proprietary information which is protected by copyright.
Table of Contents Chapter 1 Introduction to the Digital Instruments MultiMode SPM 1 1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 1.2 Safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.2.1 Six Rules of Safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.2.2 Safety Requirements . . . . . . . . . . . . . . . . . . . . . . .
2.5 Review of TappingMode AFM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 2.5.1 General Operating Concepts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 2.5.2 Optimizing the TappingMode AFM Signal after Engagement . . . . . . . . . . . 45 2.6 Terms and Abbreviations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 Chapter 3 Setup & Installation 49 3.1 Installing the MultiMode SPM . . . . . . . . . . . . . . . . . . . . . .
6.4 Beyond the Basics of AFM Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . 98 6.4.1 Cantilever Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98 6.5 Optimization of Scanning Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . 99 6.5.1 6.5.2 6.5.3 6.5.4 6.5.5 6.5.6 Chapter 7 Data type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99 Gain settings . . . . . . . . . . .
8.4 Troubleshooting Tips. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138 8.4.1 8.4.2 8.4.3 8.4.4 8.4.5 Cantilever Tune Plot Looks Poor: Loose Probetip . . . . . . . . . . . . . . . . . . . 138 Laser Sum Signal Absent or Weak: Air Bubbles . . . . . . . . . . . . . . . . . . . . . 138 Poor Image Quality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138 Lost Particulate Samples: Attracted to Cantilever. . . . . . . . . . . . . . . . . .
10.2.4 10.2.5 10.2.6 10.2.7 Chapter 11 Understanding the Color Scale . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171 Using TMR Voltage to Measure Friction . . . . . . . . . . . . . . . . . . . . . . . . . 172 Enhancing the LFM Data by Subtracting Two Images . . . . . . . . . . . . . . . 172 Height Artifacts in the Signal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173 Force Imaging 175 11.1 Force Plots—An Analogy. . . . . . . . . . . . . . . . . . . . . . .
12.5 Use of LiftMode with TappingMode . . . . . . . . . . . . . . . . . . . . . . . . . 222 12.5.1 12.5.2 12.5.3 12.5.4 12.5.5 Chapter 13 Main Drive Amplitude and Frequency selection. . . . . . . . . . . . . . . . . . . . 222 Setpoint Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 222 Interleave Drive Amplitude and Frequency Selection. . . . . . . . . . . . . . . . 223 Amplitude Data Interpretation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Chapter 15 Calibration, Maintenance, Troubleshooting and Warranty 271 15.1 SPM Calibration Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 275 15.1.1 Theory Behind Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 276 15.1.2 Calibration References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 280 15.2 Calibration Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 281 15.2.1 15.
15.11.3 Head does not engage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 314 15.11.4 Head engages immediately . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 315 15.11.5 Displacement of material. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 315 15.11.6 Lines in the image . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 315 15.11.7 Problems with silicon nitride cantilevers. . . . . . . . . .
Rev.
List of Figures Chapter 1 Introduction to the Digital Instruments MultiMode SPM . . . . . . . . .1 Figure 1.1a MultiMode SPM System Components . . . . . . . . . . . . . . . . . . . . .3 Figure 1.2a Safety Symbols Key . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5 Chapter 2 SPM Fundamentals for the MultiMode . . . . . . . . . . . . . . . . . . . . . .17 Figure 2.1a Figure 2.1b Figure 2.1c Figure 2.1d Figure 2.1e Figure 2.1f Figure 2.1g MultiMode SPM System Hardware . . . . . . .
List of Figures Chapter 4 Cantilever Preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57 Figure 4.1a Figure 4.1b Figure 4.1c Figure 4.1d Figure 4.1e Figure 4.1f Figure 4.2a Figure 4.2b Figure 4.2c Figure 4.2d Figure 4.2e Chapter 5 Silicon Cantilever Substrates in Wafer. . . . . . . . . . . . . . . . . . . . Silicon Cantilever—Theoretical Tip Shape . . . . . . . . . . . . . . . . Silicon Probe Tip Profile Artifact (front to back). . . . . . . . . . . .
List of Figures Chapter 7 TappingMode AFM. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .103 Figure 7.1a Tapping Cantilever in Free Air . . . . . . . . . . . . . . . . . . . . . . . . .104 Figure 7.1b Tapping cantilever on sample surface. Note deflection of cantilever and return signal (exaggerated).. . . . . . . . . . . . . . . . . . . . . .104 Figure 7.2a Select Show All Items . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .105 Figure 7.2b Enable Parameters. . .
List of Figures Figure 9.5c STM current image of layered crystal a-RuCl3. Scan size = 4.48nm, Itun = 1.5pA, Vbias = 42mV. . . . 161 Figure 9.5d STM height image of alkanethiol layer on Au (111) substrate. Scan size = 178.5nm, Itun = 2pA, Vbias = 1V. (Courtesy of Dr. I. Tuzov, NCSU) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162 Figure 9.5e Molecular-scale STM current image of alkanethiol layer on Au (111) substrate. Scan size = 10.0nm, Itun = 13pA, Vbias = 1V. (Courtesy of Dr. I.
List of Figures Chapter 13 Magnetic Force (MFM) Imaging . . . . . . . . . . . . . . . . . . . . . . . . . . .225 Figure 13.1a MFM LiftMode principles . . . . . . . . . . . . . . . . . . . . . . . . . . .226 Figure 13.1b Basic Extender for NanoScope III, IIIa and Quadrex Extender for NanoScope IIIa Controllers (required for MFM phase detection and frequency modulation) . . . . . . . . . . . . . . . . . . . . . .227 Figure 13.2a Cantilever Tune for phase detection and frequency modulation228 Figure 13.
List of Figures Figure 14.3k Jumper configuration for applying external voltage to sample (for systems with the Basic Extender Module).. . . . . . 255 Figure 14.4a Toggle Switches on Back of Basic Extender Module . . . . . . 256 Figure 14.4b Phase detection Cantilever Tune (for systems with the Basic Extender Module installed)257 Figure 14.4c Shift in Phase at Fixed Drive Frequency . . . . . . . . . . . . . . . . 258 Figure 14.
List of Figures Figure 15.12b Figure 15.12c Figure 15.12d Figure 15.16a Figure 15.16b Chapter 16 Rev. B Rings During High Frequency Operation . . . . . . . . . . . . . . .321 Dull or Dirty Tip . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .322 Double or Multiple Tips . . . . . . . . . . . . . . . . . . . . . . . . . . . .322 MultiMode Scanner. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .329 Stabilizing screw for securing the vertical scanner to the support ring.
Chapter 1 Introduction to the Digital Instruments MultiMode SPM The following sections are covered in this chapter: • Introduction: Section 1.1 • Safety: Section 1.2 • Six Rules of Safety: Section 1.2.1 • Safety Requirements: Section 1.2.2 • Safety Precautions: Section 1.2.3 • Microscope Specifications: Section 1.3 • Image Size and Resolution: Section 1.3.1 • Scanning Techniques with the MultiMode SPM: Section 1.3.2 • Controller Electronics and Auxiliary Channels: Section 1.3.3 Rev.
Introduction to the Digital Instruments MultiMode SPM Introduction 1.1 Introduction The MultiMode scanning probe microscope (MM-SPM) is designed for imaging small (approx. 1.5cm dia.) samples using a series of interchangeable scanners and is able to provide images from the atomic scale to 175µm in size. This manual is designed to assist operators with using the MMSPM. Refer to the Command Reference Manual (004-122-000) (or appropriate software manual) for more information.
Introduction to the Digital Instruments MultiMode SPM Introduction Figure 1.1a MultiMode SPM System Components Computer Control monitor Display monitor 037 NanoScope Controller Keyboard Rev.
Introduction to the Digital Instruments MultiMode SPM Safety 1.2 Safety 1.2.1 Six Rules of Safety Here is a summary of precautions to follow during your learning phase. If you follow the rules below, the MM-SPM can come to little harm and you may feel free to experiment boldly. Read the manuals! Even if you have prior experience with the MM-SPM, be sure to read Chapter 1 – Chapter 5 in this manual before doing any imaging work. Each of the remaining chapters are dedicated to specific types of imaging.
Introduction to the Digital Instruments MultiMode SPM Safety Check all connections before hardwiring external equipment External equipment which is hard-wired into the MM-SPM, such as for EFM and ECSTM imaging, requires special cautions. To prevent damage to your microscope, always check connections carefully against documentation before energizing the system. For more information, see Support Note 210.
Introduction to the Digital Instruments MultiMode SPM Safety 1.2.3 Safety Precautions Because the MultiMode SPM features independently motorized components, it is crucial that operators become familiar with precautions to avoid injury to themselves and/or damage to samples. This section of the manual should be read by ALL persons working with or around the system.
Introduction to the Digital Instruments MultiMode SPM Safety CAUTION: Please contact Veeco before attempting to move the MultiMode SPM system. ATTENTION: Il est impératif de contacter Veeco avant de déplacer le MultiMode SPM. VORSICHT: Bitte kontaktieren Sie Veeco bevor Sie das MultiMode SPM System transportieren. WARNING: Voltages supplied to and within certain areas of the system are potentially dangerous and can cause injury to personnel.
Introduction to the Digital Instruments MultiMode SPM Safety WARNING: The MultiMode SPM contains a diode laser with an output of less than 1.0mW at 670nm. AVERTISSEMENT:Le microscope “MultiMode SPM” est équipé d’une diode laser dont la puissance de sortie est inférieure à 1mW à 670nm. WARNUNG: Das MultiMode SPM ist mit einem Halbleiterlaser ausgerüstet, dessen Ausgangsleistung kleiner ist als 1.0mW bei 670nm. WARNING: Do not use acetone to clean the MultiMode SPM.
Introduction to the Digital Instruments MultiMode SPM Safety WARNING: The MultiMode SPM uses a halogen lamp to illuminate samples. Exposure to non-ionizing radiation from this lamp is well within the current exposure guidelines published by the American Conference of Governmental Industrial Hygienists (ACGIH). Typical IR exposure to the user from the sample illuminator is less than 3 mW/cm2. UV radiation is not detectable.
Introduction to the Digital Instruments MultiMode SPM Safety Microscope To avoid operator injury and equipment damage, observe the following cautions regarding the MultiMode microscope. 10 CAUTION: If you use the equipment in a manner not specified by the manufacturer, you can impair the protection provided by the instrument. CAUTION: Stage microscopes feature an automated X-Y stage and Z-axis capable of programmed movement. The movements of all axes are slow, but are capable of exerting high forces.
Introduction to the Digital Instruments MultiMode SPM Safety WARNING: Do not attempt repairs on electrical components. If it is necessary to enter the electrical chassis for any reason (e.g., to replace a computer card), power-down the entire system and disconnect it from its power source. AVERTISSEMENT:Ne pas essayer de réparer les parties électroniques.
Introduction to the Digital Instruments MultiMode SPM Safety Sample Safeguards 12 CAUTION: Do not change samples in the middle of operation. Verify that the stage is clear of tools, objects, and debris at all times. Use alcohol wipes periodically to keep the stage clean of dust. Dispose of wipes in an appropriately labelled solvent-contaminated waste container. ATTENTION: Ne pas changer d’échantillon en cours d’utilisation. Vérifier que la platine n’est pas encombrée, par des outils par exemple.
Introduction to the Digital Instruments MultiMode SPM Microscope Specifications 1.3 Microscope Specifications The MultiMode SPM can be fitted with any of several scanners, depending upon the imaging requirements. Generally, the smaller the scan, the smaller the scanner used. This is especially true of atomic-scale scans, which are most often conducted with “A” or “E” scanners. Larger scans are normally performed using “J” scanners. 1.3.
Introduction to the Digital Instruments MultiMode SPM Microscope Specifications • Magnetic Force Microscope (MFM)—Measures magnetic force gradient distribution above the sample surface. Performed using LiftMode to track topography (Basic Extender Module recommended for NanoScope III or IIIA). See Chapter 13. • Electric Force Microscope (EFM)— Measures electric field gradient distribution above sample surfaces.
Introduction to the Digital Instruments MultiMode SPM Microscope Specifications 1.3.3 Controller Electronics and Auxiliary Channels The MultiMode utilizes a NanoScope Controller having a digital signal processor (DSP) with a 20MHz peak rate for arithmetic operations. The MultiMode is equipped with four auxiliary digitalto-analog converters (DACs). Three DACs have ±10V outputs, and one DAC has a ± 12V and ±220V outputs; all four channels have 16-bit resolution.
Introduction to the Digital Instruments MultiMode SPM Microscope Specifications 16 MultiMode SPM Installation Manual Rev.
Chapter 2 SPM Fundamentals for the MultiMode The following sections are covered in this chapter: • Hardware: Section 2.1 • MultiMode SPM: Section 2.1.1 • SPM Head: Section 2.1.2 • Scanners: Section 2.1.3 • Tipholders: Section 2.1.4 • Probes: Section 2.1.5 • Control Mechanisms and Feedback: Section 2.2 • A brief history of SPM control mechanisms: Section 2.2.1 • Feedback Gains: Section 2.3 • Proportional and Integral Gain—An Analogy: Section 2.3.1 • Proportional Gain: Section 2.3.
SPM Fundamentals for the MultiMode Hardware • Reexamining the Control Loop: Section 2.4.1 • General Description of Main Menu Items: Section 2.4.2 • User Example: Section 2.4.3 • Review of General Operating Concepts: Section 2.4.4 • Review of TappingMode AFM: Section 2.5 • General Operating Concepts: Section 2.5.1 • Optimizing the TappingMode AFM Signal after Engagement: Section 2.5.2 • Terms and Abbreviations: Section 2.6 2.
SPM Fundamentals for the MultiMode Hardware 2.1.1 MultiMode SPM The heart of the system is the SPM itself, shown below (see Figure 2.1b) Figure 2.1b MultiMode SPM Photodiode adjustment knob Laser adjustment knobs SPM tip Head Tipholder Sample Scanner (Shown: “A”) Coarse adjustment screws X-Y head translator Retaining springs Scanner support ring Motor control switch Mode selector switch A-B A+B display Base (A+C)-(B+D) A+B+C+D display Signal sum display (elliptical) Rev.
SPM Fundamentals for the MultiMode Hardware 2.1.2 SPM Head Figure 2.1c below shows a MM-SPM head with various adjustment knobs. The head and attached X-Y stage are kinematically mated to the scanner via three contact points. A pair of retaining springs hold down the head, allowing it to be raised and lowered using adjustment screws threaded through the scanner body. On older models, two screws are manually adjusted by the operator; the rear-most screw is motorized and under computer control.
SPM Fundamentals for the MultiMode Hardware Figure 2.1d Quad Photodetector Arrangement Laser LFM Photodetector segments Photodetector B Mirror A AFM C D Cantilever 2.1.3 Scanners Figure 2.1e below shows the various, interchangeable scanners. The maximum scan size and resolution of images depend upon the choice of scanner (see chart). Longer scanners, e.g., type “J,” yield larger scan sizes; shorter scanners, e.g., type “A,” offer smaller images down to the atomicscale.
SPM Fundamentals for the MultiMode Hardware Because each scanner exhibits its own unique piezo properties, each has its own parameter file. When scanners are changed, the parameter file for the new scanner is changed along with it, ensuring maximum accuracy at any scan size. Loading new parameter files requires only a few seconds. Table 2.1a describes the range capabilities of each MultiMode SPM scanner. Table 2.1a MultiMode SPM Scanner Specifications Model Scan Size Vertical Range AS-0.5 (“A”) 0.
SPM Fundamentals for the MultiMode Hardware AC voltages applied to the scanner crystal X-Y axes produce a raster-type scan motion as represented in Figure 2.1g. The horizontal axis presented on the display monitor is referred to as the “fast axis” (in this example, the X-axis, although either axis may be designated as the “fast axis.”) and scans at a Scan rate entered by the user. The orthogonal axis is known as the “slow axis” (in this example, the Y-axis). Figure 2.
SPM Fundamentals for the MultiMode Hardware 2.1.4 Tipholders The sample and mode of SPM to be performed dictate the choice of tip and tipholder. For example, if contact AFM is to be used for imaging, a silicon nitride cantilever mounted in a standard tipholder is the usual choice. If TappingMode is to be used for imaging a biological specimen in fluid, a special fluid cell is employed. STM utilizes a special tipholder, having a tiny tube holder adapted for holding wire tips.
SPM Fundamentals for the MultiMode Hardware 2.1.5 Probes Probes come in a variety of sizes, shapes and materials and are chosen according to the chosen type of imaging. Wire Probes STM probes usually consist of wire, cut and/or etched to produce atomically sharp tips at one end. Usually these are made from tungsten or platinum-iridium alloy wires. A potential is established so that electrons flow between the tip and sample. A similar type of wire probe is used for lithography.
SPM Fundamentals for the MultiMode Hardware Cantilevered Probes Most SPM work is done using cantilevered probes. These consist of a flexible cantilever extending from a rigid substrate, to which a tip has been attached. In contact AFM, the cantilever flexibility acts as a nanometric spring, allowing the tip to measure surface forces. In TappingMode, the probe is oscillated up and down at its resonant frequency while its amplitude and phase are monitored. Figure 2.
SPM Fundamentals for the MultiMode Hardware Cantilevered Probes—MFM Another variation of the TappingMode tip is the MFM probe. This is basically a crystal silicon TappingMode probe having a magnetic coating on the tip. As the magnetized tip oscillates through magnetic fields on the sample surface, it modulates the cantilever’s phase and frequency. These are monitored, providing a measure of magnetic field strength and providing images of magnetic domains.
SPM Fundamentals for the MultiMode Control Mechanisms and Feedback 2.2 Control Mechanisms and Feedback To produce quality images, the SPM must be capable of controlling the tip-sample interaction with great precision. This is accomplished with the use of an electronic feedback loop, which safeguards the tip and sample by keeping forces between them at a user-specified Setpoint level.
SPM Fundamentals for the MultiMode Control Mechanisms and Feedback an electronic image. The main disadvantage of this method was difficulty in aligning the contacting tip’s cantilever and the STM tip directly above it. Figure 2.2b Early Contact AFM which allowed Imaging Non-conductive Samples STM tip Flexible cantilever Sample AFM tip Preceding the first SPMs, some profilometers had relied upon optical methods to monitor the rise and fall of a sharp stylus over sample surfaces.
SPM Fundamentals for the MultiMode Feedback Gains 2.3 Feedback Gains The feedback system used to control tip-sample interactions and render images must be optimized for each new sample. This is accomplished by adjusting various gains in the SPM’s feedback circuit. This section discusses gains and how they are used to obtain images. 2.3.
SPM Fundamentals for the MultiMode Feedback Gains 2.3.2 Proportional Gain Proportional gain means that something is done proportionally in response to something else.
SPM Fundamentals for the MultiMode Feedback Gains 2.3.3 Integral Gain Integral gain is used to correct the cumulative error between a system and its target state. In the case of the balloon, it is not enough to use only proportional gain. As we have seen, the balloon will maintain a constant error around the setpoint altitude if it relies on proportional gain alone.
SPM Fundamentals for the MultiMode Feedback Gains 2.3.6 Setpoint In our ballooning example, “setpoint” referred to the target altitude to be maintained. In scanning probe microscopy, “setpoint” refers to how much tip-sample force is maintained. There are two ways of defining setpoint, depending upon whether one is referring to contact AFM or TappingMode.
SPM Fundamentals for the MultiMode Feedback Gains permitted non-conducting surfaces to be imaged. Tunneling current was now used indirectly to monitor a cantilevered tip as it profiled samples. Although this method allowed imaging of nonconducting samples, it was unreliable due to adjustment difficulties with the STM probe and cantilever flexion. The next great leap in SPM design which presaged the present state of the art was the introduction of light beam deflection.
SPM Fundamentals for the MultiMode Feedback Gains a similar trace of an irregular, random surface would reveal that each scan line bears little resemblance to its adjacent line. The entire purpose of LookAhead gain is to take full advantage of regular features by using every line to anticipate the next one. In NanoScope software, the LookAhead gain value may be adjusted between a range of 0 (off) to 16 (maximum).
SPM Fundamentals for the MultiMode Feedback Gains new old where z acc is the new average error calculated by adding the old average error z acc to the product new of the integral gain times the error. The running average represented by z acc maintains itself continually until one or more of the major scanning parameters is changed by the operator. Whenever major scan parameters are changed (e.g., Setpoint), the error accumulator is dumped and begins a new running average.
SPM Fundamentals for the MultiMode Control Parameters and Feedback To better understand what is being viewed when selecting different Data types, consider the diagram below: height Signal out (to Z piezo) Feedback Controller Signal in (Inaux) Signal in (In0) Microscope deflection, amplitude, current auxiliary: phase, frequency, deflection during TappingMode, friction.
SPM Fundamentals for the MultiMode Control Parameters and Feedback comparator circuit through an analog-to-digital (A/D) converter. It is programmed to keep the two inputs of the comparator circuit equal (0V). An output voltage generated by the computer continuously moves the piezoelectric transducer in the Z direction to correct for differences read into the A/D converter. This closed-loop feedback control is the heart of the imaging portion of the control station. 2.4.
SPM Fundamentals for the MultiMode Control Parameters and Feedback computer to think that the SPM output is further away from the setpoint reference than it really is. The computer essentially overcompensates for this by sending a larger voltage to the Z piezo than is truly needed. This causes the piezo scanner to move faster in Z. This is done to compensate for the mechanical hysteresis of the piezo element.
SPM Fundamentals for the MultiMode Control Parameters and Feedback 3. The Vertical Deflection (A-B) voltage differential is sensed by the feedback electronics, causing a dropped voltage to the Z piezo crystal—the piezo retracts. As the Z piezo retracts, the cantilever recenters the laser beam onto the photodiode array (A = B). 4. As the tip encounters a decline in the sample topology, the tip drops. This directs more of the beam onto the “B” portion of the photodiode array.
SPM Fundamentals for the MultiMode Control Parameters and Feedback Figure 2.4a Contact AFM Concepts (Steps 1-5 exaggerated.) Photodiode Array Photodiode “B” Mirror Laser Photodiode “A” Laser beam Tip A-B (Vertical Deflection) Voltage O Volts Setpoint Voltage Reflected Laser Beam Sample Z piezo A/D Converter Scanner Tube Computer “B” “A” Step 1 Step 2 Step 4 Srep 3 Step 5 The AFM always first engages in the repulsive region of its operating range.
SPM Fundamentals for the MultiMode Control Parameters and Feedback indication of a good engagement is a distinct jump of about 1V from the Vertical Deflection (A-B) voltage to the Setpoint voltage. The displayed image is an average of the corrections made to Z in a given display period (number of samples menu item). The two gains are set to values to effectively “tune” the feedback response to the particular sample topology.
SPM Fundamentals for the MultiMode Review of TappingMode AFM 2.5 Review of TappingMode AFM 2.5.1 General Operating Concepts One advantage of TappingMode AFM is an absence of frictional forces which exert torque on the cantilever. Unlike traditional contact AFM, the feedback loop keeps a vibrating cantilever at a constant amplitude, rather than keeping a cantilever at a constant deflection. The tip on the cantilever is modulated through mechanical excitation at its resonance.
SPM Fundamentals for the MultiMode Review of TappingMode AFM Figure 2.
SPM Fundamentals for the MultiMode Review of TappingMode AFM 2.5.2 Optimizing the TappingMode AFM Signal after Engagement The figures on the bottom of Figure 2.5a show the relationship between the RMS and the setpoint voltages. There are some basic rules to remember: 1. The setpoint voltage is always lower than the RMS voltage. 2. The difference between the RMS voltage when the tip is off the surface, and the setpoint voltage dictates the amount of damping or “tapping force.
SPM Fundamentals for the MultiMode Terms and Abbreviations 2.6 Terms and Abbreviations This section contains a brief list of terms and abbreviations to assist the reader. Other terms and abbreviations are referenced in the Index at the back of this manual. AFM—Atomic force microscopy; atomic force microscope. aliasing—Electronic image error due to differences in resolution between surface features and the pixels used to represent them.
SPM Fundamentals for the MultiMode Terms and Abbreviations integral gain—Amount of correction applied in response to the average error between setpoint force and actual force measured by the detector. LFM—Lateral force microscopy; lateral force microscope. Frictional measurements of surfaces based upon a tip’s lateral and torsional response.
Chapter 3 Setup & Installation The following sections describe the setup and installation of your MultiMode microscope: • Installing the MultiMode SPM: Section 3.1 • Component List: Section 3.2 • Unpack The System: Section 3.2.1 • Vibration Isolation: Section 3.2.2 • System Power Up: Section 3.2.3 3.1 Installing the MultiMode SPM Set up the computer, main controller and two monitors as described in this chapter.
Setup & Installation Component List • Vibration isolation pad • Scanner calibration reference: XYZ, 10µm x 10µm, 200nm vertical (all scanners); Mica sample (“A” scanners); 1µm XY grating (“E” scanners) • Package of Contact Mode cantilevers - silicon nitride type • Package of TappingMode cantilevers - single crystal silicon • MultiMode SPM head (see Figure 3.2a) Figure 3.2a MultiMode SPM Head • MultiMode SPM scanner (with retaining springs if not a vertical engage scanner).
Setup & Installation Component List 3.2.1 Unpack The System The NanoScope system is normally shipped in five separate boxes. Each monitor is shipped in its own box, the computer and controller are shipped in separate boxes, and the MultiMode SPM, cables and hardware are shipped in one box (see Figure 3.2b). Figure 3.2b Typical MultiMode Shipping Boxes Each monitor is shipped separately. The SPM is packed in a separate box. 1. Clear a table for the microscope.
Setup & Installation Component List Figure 3.2c Hardware Setup Display monitor Control monitor NanoScope controller Computer Keyboard Mouse SPM (Extender not shown) CAUTION: The NanoScope controller will overheat if the computer or controller ventilation holes are blocked or if the controller is exposed to heat from an outside source. 3. Remove the remaining components and locate them using the layout above as a guide.
Setup & Installation Component List 2. Connect computer cables (monitors, keyboard, mouse and controller) as shown below (see Figure 3.2d). Figure 3.2d Rear View of Computer on Standard MultiMode Systems Power *Verify that voltage selection switch is set correctly for your voltage. Mouse Keyboard Display monitor Control monitor NanoScope controller Note: Printers are also user-supplied. Serial ports COM1 and COM2 may be configured by the user for peripheral equipment. 3.
Setup & Installation Component List 4. The SPM is connected to the front of the controller with the 37-pin ribbon connector. Verify that the ribbon cable is securely connected; otherwise, the microscope may not engage or exhibit other problems. Note: If a Basic Extender Module is included, install it now between the SPM and controller. Verify that it has been properly configured per instructions provided in Installation of the Extender Electronics Modules: Section 13.
Setup & Installation Component List Figure 3.2f Installing the Head (Shown: “A” scanner) Plug head into support ring here. Front View Rear View 7. Recheck all cable connections. Review the steps above one last time to ensure that all connections are properly made. Make certain that the controller cable is NOT plugged into the parallel port of the computer or damage to the electronics will result. 3.2.
Setup & Installation Component List 3.2.3 System Power Up CAUTION: The following section is required only during installation or after servicing and should NOT be used by untrained personnel. Prepare the System for Power-up 1. Verify that the power cord is plugged into a grounded power receptacle. 2. Verify the following electrical requirements: • 1.8W; single phase • 100V, 120V or 240V duplex outlet • dedicated circuit • 50/60Hz 3.
Chapter 4 Cantilever Preparation The MultiMode microscope comes furnished with etched silicon cantilever substrates for TappingMode AFM and silicon nitride cantilevers for Contact AFM Modes. In both cases, the cantilever probes should be inspected under the microscope when being used for the first time to get a better understanding of how the probes and substrates are connected and taken apart. The procedure for removing individual substrates from the wafer varies depending on the wafer.
Cantilever Preparation Silicon Cantilever Substrates 3. It may be convenient to break several substrates from the wafer at one time. Extras may be safely stored in a specially prepared closable container. At the bottom of the container, place X4-grade, GEL-PAK™ adhesive strips. Place the substrates, tips facing up, on the adhesive to permit easy removal of the substrates when needed. Cover the container when not in use. Figure 4.
Cantilever Preparation Silicon Cantilever Substrates 4.1.1 Tip Shape of Etched Silicon Probes Etched silicon probes provide the highest aspect ratio and most consistent tip sharpness of the probes supplied at present. There are some subtleties in general shape that should be understood to gain the best advantage from the etched silicon tips when imaging samples with steep walls over steps of 100nm to several microns in height. Figure 4.1b Silicon Cantilever—Theoretical Tip Shape 17.0° 17.0° TIP 25.
Cantilever Preparation Silicon Cantilever Substrates Figure 4.1c Silicon Probe Tip Profile Artifact (front to back) Scan line produced using a theoretical probe tip shape on a 1 - 2 µm deep vertical wall trench Scan direction = 0 deg. 10° 11 ˚ 55° 80° Scan Line Profile 1 µm - 2 µm Deep Trench Note: Any wall angle on the left wall that is > 55 deg. will be shown as 55 deg. in the image.
Cantilever Preparation Silicon Cantilever Substrates Figure 4.1d Silicon Probe Tip Step Profile Artifact (side-to-side) Scan line produced using theoretical probe tip shape on a 1 - 2 µm deep vertical wall trench Scan direction = 90 deg. 73° 73° Scan Line Profile 1 - 2 µm Deep Trench Note: Any wall angle that is > 73 deg. will be shown as 73 deg. in the image. Measurements of line pitch are often best measured using the side-to-side faces of the tip, which exhibits symmetry.
Cantilever Preparation Silicon Cantilever Substrates Figure 4.1e Silicon Probe—Common Shape Artifact 20 - 30° Due to the nature of the etching process that shapes the tip, there is often a short angled ridge near the highest point of the tip. The exact length of the ridge is variable but rarely exceeds 0.5µm in total length. It is inclined steeply, so that for reasonably flat surfaces the highest point is the only one which interacts with the surface.
Cantilever Preparation Silicon Cantilever Substrates Figure 4.1f Common Silicon Probe Profile—Resultant Scan Artifact Subsequent scan line produced by using the realistic probe tip shape 10° 11˚ 55° 70 - 80° Scan Line Profile 1 µm - 2 µm Deep Trench Note: Any wall angle on the left wall that is > 55 deg. will be shown as 55 deg. in the image. Any wall angle on the right wall that is >70-80 deg. will be shown as 70 -> 80 deg. in the image. Shown above in Figure 4.
Cantilever Preparation Silicon Nitride Cantilever Substrates 4.2 Silicon Nitride Cantilever Substrates The silicon nitride cantilever substrates used in Contact Mode can be removed from the wafer with the following procedure. Note that the cantilevers are stored tip-side-up and that the silicon is very brittle. Contacting the cantilever during this operation will almost certainly break it off of the substrate. 1. Verify that the wafer is oriented with the tips facing upward (gold coated surface down).
Cantilever Preparation Silicon Nitride Cantilever Substrates Figure 4.2b Substrate Break-Off Cantilever Cantilever SubstrateSubstrate Hold down here with Edge of Glass end of cotton swab Slide Edge of Glass Slide Grip here with wide tweezers. Rotate downward until substrate snaps off. Saw Cuts Saw-Cuts Press Here to Break Off Extra substrates are easily stored in a covered container. The shipped substrates are held on X0grade, GEL-PAK™ adhesive strips.
Cantilever Preparation Silicon Nitride Cantilever Substrates 4.2.1 Tip Shape of Silicon Nitride Probes Silicon nitride probes provide low cost and durable probes suitable for Contact Mode imaging. There are some subtleties in general shape that should be understood to gain the best advantage from the silicon nitride tips when imaging samples with steps of 0.1 to several microns in height. Bear in mind that the probe tip is approximated by a pyramid formed by intersecting <111> planes in silicon.
Cantilever Preparation Silicon Nitride Cantilever Substrates Figure 4.2e Silicon Nitride Cantilevers—Sidewall Profile Effect 45.0° 65.0° 11˚ 10.0° Scanning Profile Two types of silicon nitride cantilever probes are available: standard and oxide-sharpened tip processes.
Chapter 5 Head, Probe and Sample Preparation This chapter provides instructions for head, probe and sample preparation for imaging with the MultiMode SPM. It describes how to remove and install the microscope head, how to change the probe tipholder, how to mount the probe, load and position samples, and a general description of how to engage and withdraw the tip. These procedures are common for most types of MultiMode SPM imaging.
Head, Probe and Sample Preparation Other chapters in this manual describe how to perform specific types of imagery. The table below outlines where you will find additional information for each type of imagery. If you are new to SPM and want to practice, we suggest you begin with contact AFM in Chapter 6.
Head, Probe and Sample Preparation WARNING: During and prior to set up of the laser, it is especially important to avoid looking directly at the laser beam or at the laser spot. The laser head should never be plugged into the microscope control electronics unless the head is installed in the Z-stage mount. Care should be taken when highly reflective samples are inserted onto the chuck. Avoid looking at all reflected laser light.
Head, Probe and Sample Preparation Initial Preparation for Contact AFM Imaging 5.1 Initial Preparation for Contact AFM Imaging 5.1.1 Prepare the Sample Verify that your sample will fit atop the scanner tube and is less than 8mm thick. If you already have prior experience with loading samples into the MultiMode SPM system, load your sample now. Otherwise, read the next section for suggestions on how to prepare and load small samples.
Head, Probe and Sample Preparation Initial Preparation for Contact AFM Imaging 5.1.2 Load the Sample Remove Head and Load Sample 1. If the head is not already removed, do so now by unfastening the retaining springs on either side and unplugging the head’s micro-D connector. 2. Gently lift the head off and set aside. This will expose the top of the scanner tube. 3. Mount the sample puck with the calibration standard atop the scanner tube. An internal magnet supplied with most units holds the puck down.
Head, Probe and Sample Preparation Initial Preparation for Contact AFM Imaging Figure 5.1c Head is Held Securely Using Retaining Springs Reattach retaining springs (2) Check Head for Free Vertical Movement Verify basic function of the motorized Z-axis by toggling the Up switch on the MultiMode base (see Figure 5.1d). This activates the leadscrew at the rear of the unit to lift the head upward.
Head, Probe and Sample Preparation Initial Preparation for Contact AFM Imaging 5.1.3 Load Probe in Tipholder • Contact Mode: Install a silicon nitride probe tip in the AFM tipholder. Figure 5.1e shows the AFM tipholder. Detailed procedures for silicon nitride cantilever substrate preparation are given in Chapter 4, including a description of the procedure to break out substrates from the wafer.
Head, Probe and Sample Preparation Initial Preparation for Contact AFM Imaging Figure 5.1f Underside Detail of Fluid Cell Probe Wire clip Lift wire clip by pressing plunger on opposite side of tipholder. Insert probe with tweezers, then release clip. Load Probe in Tipholder Refer to Figure 5.1f. Turn the tipholder upside down with the groove facing up as shown. Apply gentle upward pressure against the plunger to lift the spring clip.
Head, Probe and Sample Preparation Initial Preparation for Contact AFM Imaging 5.1.4 Install the Tipholder Figure 5.1g Install Tipholder in Head without Touching the Sample Rotate clamping screw CW (rear side of head) to secure tipholder (Rear view) Clamping screw Once the tipholder is loaded with a probe (see Figure 5.1.3 above), the tipholder is placed inside the SPM’s head and clamped into position using the clamping screw at rear of head. 1.
Head, Probe and Sample Preparation Laser Alignment 5.2 Laser Alignment This section describes two methods for aligning the laser for all modes except STM. The first method uses an Optical Viewing Microscope (OMV). The second method is a “projection” method. In the projection method you remove the MultiMode head and shine a laser onto a piece of white paper, producing diffraction patterns. The interpretation of these patterns serves as a guide to aligning the laser.
Head, Probe and Sample Preparation Laser Alignment Figure 5.2a Laser Alignment with Piece of Paper 4. Reposition the laser with the screws on top of the optical head, if necessary. 5.2.2 Method 2: The Projection Method CAUTION: Turn down the illuminator intensity before proceeding with laser alignment. You can also align the laser by moving the laser beam relative to the cantilever while observing the laser spot on a piece of white paper below the optical head.
Head, Probe and Sample Preparation Laser Alignment Etched Silicon Tips (TappingMode) 1. In this procedure, shining the laser beam on a piece of white paper serves as a guide to aligning the laser beam with the end of the cantilever. CAUTION: Use extreme caution if you choose to remove the optical head and hold it over a piece of paper. Hold the head firmly, and be mindful of the wire between the head and base.
Head, Probe and Sample Preparation Laser Alignment 8. Verify the laser spot by placing a piece of paper in front of the photodetector (see Section 5.2.1, Step 3). If necessary, reposition the laser with the front-rear and back-left knobs. Silicon Nitride Tips (Contact Mode AFM) 1. In this procedure, shining the laser beam on a piece of paper serves as a guide to aligning the laser beam with the end of the cantilever.
Head, Probe and Sample Preparation Laser Alignment 5. If the laser is positioned between a pair of legs of one cantilever (laser spot on surface below) turn the front-right laser control knob counter-clockwise to move the laser left in the X direction until the laser spot disappears on the surface below (see Point 3 in Figure 5.2c). 6.
Head, Probe and Sample Preparation Laser Alignment 5.2.3 Maximize the SUM Signal This section describes what to do after the laser spot is aligned on the cantilever and assumes knowledge of how to read voltages from the meters mounted on the front of the MultiMode base. If you are unfamiliar with reading the MultiMode voltage meters, skip ahead to MultiMode SPM Voltage Meters: Section 5.4, then return to this section. Additional information is provided in each of the various chapters on imaging.
Head, Probe and Sample Preparation Start the Microscope Program 5.3 Start the Microscope Program After any necessary software installation is complete, you are ready to start the NanoScope software. 1. To start the NanoScope software, double-click the NanoScope startup icon on the computer desktop. You will see the NanoScope software window (see Figure 5.3a), which can span one or two monitor displays.
Head, Probe and Sample Preparation MultiMode SPM Voltage Meters 3. Select the scanner you plan to use (Edit > Scanner). Note: In the Microscope Select dialog box, you can add a new set of hardware configuration parameters by clicking New or edit the parameters of the selected microscope by clicking Edit. The parameters include things such as the controller, extender, and vision system. 4. Select OK when you finish changing all microscope parameters. 5.
Head, Probe and Sample Preparation MultiMode SPM Voltage Meters RMS VERT -2.6 0.00 SUM 8.4 TappingMode or Contact AFM Output Signal (V) Vertical or Horizontal Difference Sum The bottom digital meter 2 reads differences in voltage between various segments of the photodetector. With the mode switch toggled to AFM & LFM, it indicates the voltage difference (C - D), that is, the left segments minus the right segments.
Chapter 6 Contact AFM Mode This chapter covers procedures for operating the MultiMode SPM in Contact AFM Mode. It is assumed the operator has previously prepared a Contact Mode probe and aligned the MultiMode head per instructions provided in Chapter 5 of this manual. Specific information regarding tip preparation is provided in Chapter 6; Appendix A of the Command Reference Manual contains further information regarding tips.
Contact AFM Mode Preparation Prior to Imaging • Scan size and Scan rate: Section 6.5.3 • Setpoint: Section 6.5.4 • Lowpass filter: Section 6.5.5 • Highpass filter: Section 6.5.6 6.1 Preparation Prior to Imaging 6.1.1 Adjust the Detector Offsets Verify that the MultiMode head has been fitted with a Contact Mode probe tip per instructions provided in Chapter 5 of this manual. The laser beam should already be positioned on the back of the cantilever.
Contact AFM Mode Preparation Prior to Imaging Vertical. Figure 6.1b Laser Adjustment Knobs—Top View Horizontal Adj. Laser Spot 6.1.2 Signal Settings In Contact AFM Mode, the vertical deflection (Vert Defl.) signal is used to provide the dynamic feedback signal for surface height tracking. The horizontal deflection (Horiz Defl.) is only used for lateral force measurements in Contact Mode LFM. When disengaged in Contact AFM Mode and preparing for engagement, set the detector Vert Defl.
Contact AFM Mode Preparation Prior to Imaging 6.1.3 Adjust tip height above sample surface Next, use the adjustment screws to adjust the tip height just above the sample surface. The magnifier can be used to monitor the tip while this is done. The coarse adjustment screws (if so equipped) are located in front and may be used to make gross adjustments. The tip should be positioned just high enough to reach the surface when engaged, but not so low as to risk crashing into it.
Contact AFM Mode Suggested Initial Control Settings 6.2 Suggested Initial Control Settings 6.2.1 Show All Items Before changing any parameters, you should display all of the available parameters. If you cannot view a parameter in a panel, you might need to enable this parameter. 1. Click the “minus box” in the upper left corner of the panel, and click Show all items. Figure 6.2a Select Show All Items a.Click here 045 b.Select this 2.
Contact AFM Mode Suggested Initial Control Settings 6.2.2 Initial Scan Parameter Settings Before making changes to Scan Controls panel screen parameters, go to the Other Controls panel (Panels > Other) and verify that the Microscope Mode parameter is set to Contact. Scan Controls Panel 1. Select Panels > Scan. Set the Scan size as large as desired to 1.0µm and set the X and Y offsets to 0.0. 2. Set the Scan angle to 0.
Contact AFM Mode Suggested Initial Control Settings Interleave Controls Panel If it is not already present, open the Interleave Controls Panel by selecting Panels > Interleave. Verify that the Interleave mode field is set to Disabled. (Do not attempt to set Interleave mode to Enabled at this point). Figure 6.2d Interleave Controls Panel Settings for Initial Setup (Contact Mode) Channel 1, 2 and 3 Panel On the Channel 1 panel, set Data type to Height (see Figure 6.2e).
Contact AFM Mode Suggested Initial Control Settings Feedback Controls Panel 1. Next, select Panels > Feedback. 2. Set both Integral and Proportional gain to 2.0 each and the Deflection Setpoint to 0.0V. 003 Figure 6.2f Feedback Controls Panel Settings for Initial Setup (Contact Mode) Other Controls Panel 1. Using the mouse, select Panels > Other to display the Other Controls panel. 2. Verify that the Microscope mode is set to Contact. 3. Set the Z Limit to 440V. 4. Set Units to Volts, Color table to 2.
Contact AFM Mode Initiate the Engage Command 6.3 Initiate the Engage Command Select Motor > Engage (or click the Engage icon). A pre-engage check, followed by Z-stage motor sound should be observed. If for any reason the engage aborts because the SPM head is still too far away from the surface, click on the Abort button and readjust the screws to start the tip closer to the sample surface. Assuming the tip is better positioned before engaging again, an image should begin to appear on the image monitor.
Contact AFM Mode Initiate the Engage Command What is happening? The piezo is being retracted from the Z scan start position to the Z scan start-plus-Scan size position. The Z scan start point is at the left-most portion of the plot. The Z scan start-plus-Scan size point is the right-most portion of the plot. This corresponds to the Z Center Position that was being used while scanning just before starting Force Calibration.
Contact AFM Mode Initiate the Engage Command Now adjust the Setpoint for imaging. Having the setpoint anywhere above the line where the tip is off the surface will work. The farther it is above, the more force is placed onto the sample. To adjust tip-sample force to the minimum amount, you can run in the area where the tip is actually pulling up but the liquid layer is holding the tip on the surface.
Contact AFM Mode Beyond the Basics of AFM Operation 6.3.2 Adjust Sensitivity (if required) If imaging in Deflection mode instead of Height mode, adjust the detector’s Sensitivity parameter to the cantilever as described in this section. Use the mouse to draw a line parallel to the part of the plot where the tip is on the surface. To clear the screen, click the mouse’s right button while in the graph. Click and drag line parallel to sloped portion of plot. 6.
Contact AFM Mode Optimization of Scanning Parameters type silicon nitride probes which are used in some older, interferometric microscope heads; however, they may still be used. Each silicon nitride cantilever substrate includes four cantilever probes with different sizes and spring-constants.
Contact AFM Mode Optimization of Scanning Parameters the height of the sample. Deflection data should be collected with low feedback gains so the piezo remains at a constant position relative to the sample. In this case, the tip and cantilever will be deflected by the features on the sample surface. The output fluctuations in the cantilever deflection voltage from the top and bottom photodiode segments are recorded as a measure of the variation in the sample surface.
Contact AFM Mode Optimization of Scanning Parameters 6.5.4 Setpoint The Setpoint parameter defines the desired voltage (and, therefore, the desired deflection of the cantilever) for the feedback loop. The setpoint voltage is constantly compared to the present photodiode cantilever deflection voltage to calculate the desired change in the piezo position.
Chapter 7 TappingMode AFM This chapter covers procedures for operating the MultiMode SPM using TappingMode in air. It is assumed that the operator has previously prepared a TappingMode probe tip and aligned the SPM head per instructions provided in Chapter 5 of this manual. Additional information regarding cantilever preparation is provided in Chapter 4. Note: TappingMode is disabled for users of NanoScope E configurations.
TappingMode AFM Basic Principle of TappingMode 7.1 Basic Principle of TappingMode Figure 7.1a represents a cantilever oscillating in free air at its resonant frequency. A piezo stack excites the cantilever substrate vertically, causing the tip to bounce up and down. As the cantilever bounces vertically, the reflected laser beam is deflected in a regular pattern over a photodiode array, generating a sinusoidal electronic signal.
TappingMode AFM Preparation Prior to Imaging 7.2 Preparation Prior to Imaging 7.2.1 Switch to TappingMode The microscope must be switched to TappingMode. Go to the Realtime > Microscope > Profile and select the profile TappingAFM. Toggle the selector switch on the left side of the MultiMode base to TM AFM; the tiny LED indicator on the front of the base should glow green. 7.2.2 Show All Items Before changing any parameters, you should display all of the available parameters.
TappingMode AFM Preparation Prior to Imaging 3. Click the “minus box” in the upper left corner of the panel, and click Show all items. The panel will once again appear in normal Realtime mode. 7.2.3 Check Parameters Check that the Realtime control panel parameters are set within reasonable limits for TappingMode operation. If you are uncertain what parameter settings to start with, try the values below: Panel Parameter (V) 10.8 Scan Controls 3.6 7.2 6.
TappingMode AFM Preparation Prior to Imaging 7.2.4 Adjust Laser and Photodetector Verify that the tipholder has been fitted with a TappingMode, single crystal silicon probe and aligned per instructions provided in Chapter 5 of this manual. Photodetector voltage values are displayed on meters mounted on the front of the MultiMode base. The laser photodetector is adjusted using the photodetector adjustment knobs on the left-top and left-rear of the head (see Figure 7.2c below).
TappingMode AFM Preparation Prior to Imaging Figure 7.2d Voltage meters on the MultiMode base reveal a great deal about the amplitude and alignment of the TappingMode laser signal on a tuned tip operating at its resonant frequency. Small laser signal amplitude yields low output voltage. RMS VERT 0.06 9.91 SUM 1.2 Sum voltage low due to misalignment of laser on cantilever or laser on photodetector. RMS VERT 0.28 0.
TappingMode AFM Preparation Prior to Imaging 7.2.5 Additional preparations In TappingMode, the RMS amplitude representing AC voltage signal is used to provide the dynamic feedback signal for surface height tracking. The vertical deflection signal (displayed on the “Vertical or Horizontal Difference” meter) should be close to zero (± 1.0V) prior to running Cantilever Tune and/or attempting engagement.
TappingMode AFM Preparation Prior to Imaging 031 Figure 7.2e Cantilever Tune Panels The Frequency Sweep (a plot of cantilever response as a function of applied vibrational frequency) is shown on the display monitor. The two main panels, Sweep Controls and Auto Tune Controls (see Table 7.2a), allow the operator to either manually or automatically tune the cantilever. For most purposes, the Auto Tune function will suffice.
TappingMode AFM Preparation Prior to Imaging Tuning cantilevers manually The parameter values, especially the drive frequency and the sweep width, given in the following example apply to one type of cantilever. The nominal parameter values may vary depending upon the actual cantilever used. For initial set-up, select View > Sweep > Cantilever Tune. The Sweep Controls panel should be set to the values shown in the example below (see Figure 7.2f). 013 Figure 7.
TappingMode AFM Preparation Prior to Imaging 2. If a peak in the frequency response plot does not appear, perform the following steps: • Increase the Drive amplitude to 600mV. • Increase Sweep width to the maximum value. If the peak still has not appeared, then increase the Sweep width by first increasing the Drive Frequency, then maximizing the Sweep width. If there is still no peak on the response plot, check the laser alignment. 3.
TappingMode AFM Engaging The Microscope actual setpoint value adjusted by the user prior to engage is meaningless because the operating setpoint is determined automatically during engage by the control program. 2. Select View > Image Mode, or click the Back to Image Mode button or the Image Mode icon. and the parameters set in the Cantilever Tune control panel will now appear in the Feedback Controls panel.
TappingMode AFM Engaging The Microscope 007 Figure 7.3b Suggested Other Controls Settings During TappingMode Setup 2. Move the probe to the area of interest using the X-Y translation knobs on the MultiMode head. 3. Use the meters to verify that the vertical deflection is between -1 and +1, the RMS amplitude (topmost meter) is 1-2V, and the sum voltage is greater than 1V. 4. The operator should now be ready to engage. Go to the upper Realtime menu bar and click on Motor followed by Engage.
TappingMode AFM Withdrawing the Tip 7.4 Withdrawing the Tip Select Withdraw from the Motor menu. The SPM will stop scanning, then ascend approximately 10µm. If more clearance between tip and sample is desired, toggle the Up / Down switch on the top-right side of the MultiMode base. Never withdraw samples without carefully observing that the tip has adequate clearance during the entire sample removal sequence. 7.
TappingMode AFM Beyond Basics with Resonating Techniques At Setpoint 1 the operating point is only slightly lower than the free vibration amplitude. This has the advantage of dissipating very little energy to the sample surface. (The drawback is that the system takes longer to recover from a given perturbation in the amplitude.) Consider the case where the tip travels off a step with a height of ∆x. At Setpoint 1 it takes longer for the amplitude of the cantilever oscillation to increase.
TappingMode AFM Beyond Basics with Resonating Techniques Figure 7.5c Scope trace with Correct Scan Rate Trace Retrace Z Range 50.00 nm/div Scan Size - 2.50 µm/div 7.5.2 Tuning the Cantilever Drive Frequency The Drive frequency selected to oscillate the cantilever plays an important role in the performance of the microscope while in TappingMode.
TappingMode AFM Beyond Basics with Resonating Techniques 7.5.3 Optimization of Scanning Parameters Careful selection of the scan parameters is important to the successful application of the MultiMode in TappingMode. In general, the effects of the various scan parameters are the same for the TappingMode as they are for contact AFM mode. The user is encouraged to review Section 5.1. which discusses parameter optimization for contact AFM. This section focuses on parameters specific to TappingMode.
TappingMode AFM Beyond Basics with Resonating Techniques Scan Size, Scan Rate, and Setpoint As discussed above, the Scan size, Scan rate, and Setpoint values have dramatic effects on the data. As in contact mode, the Scan rate must be decreased as the Scan size is increased. Scan rates of 0.5-1.0Hz should be used for large scans on samples with tall features. High scan rates help reduce drift, but they can only be used on flat samples with small scan sizes.
Chapter 8 Fluid Operation This chapter addresses scanning probe microscope (SPM) imaging of samples in fluid using a MultiMode. Refer to the following for your specific area of interest: • Introduction: Section 8.1 • General Fluid Operation: Section 8.2 • Clean Fluid Cell and O-ring: Section 8.2.1 • Select the Probe: Section 8.2.2 • Remove Organic Contamination from the Tip: Section 8.2.3 • Load the Fluid Cell with a Probe: Section 8.2.4 • Sample Mounting: Section 8.2.5 • Align the Laser: Section 8.2.
Fluid Operation • Poor Image Quality: Section 8.4.3 • Lost Particulate Samples: Attracted to Cantilever: Section 8.4.4 • Drift in AFM Image Because O-ring Slid Across Sample Surface: Section 8.4.5 • General Notes on Sample Binding: Section 8.5 • Lysozyme on Mica—A Model Procedure for Protein Binding: Section 8.6 • Protein Binding Theory: Section 8.6.1 • Protein Binding Procedure: Section 8.6.2 • Binding DNA to Mica: Section 8.7 • DNA Binding Theory: Section 8.7.1 • DNA Binding Procedure: Section 8.7.
Fluid Operation Introduction 8.1 Introduction Imaging of samples in fluid is a growing application of AFM technology. This may be prompted by a desire to minimize surface forces on delicate samples, the need to observe biological specimens in their natural, fluid environments, and/or the necessity to make real time observations of samples undergoing electrochemical reactions (ECAFM).
Fluid Operation General Fluid Operation 039 Figure 8.2a Fluid Cells TappingMode Fluid Cell Contact Mode Fluid Cell There are two fluid cells that are commonly used for fluid imaging: • Model FC is a fluid cell can be used for imaging samples in fluid using Contact Mode only. • Model MTFML is a fluid cell that can be used for imaging samples in fluid using either TappingMode or Contact Mode.
Fluid Operation General Fluid Operation The male Luer fittings can be inserted into the fluid ports on the front of the fluid cell, and the opposite side of the fitting is connected to the silicone tubing. The female Luer fittings connect the silicone tubing to the syringe. Use of the O-rings is optional. Instructions for operating the fluid cell with and without the O-ring are detailed in this chapter. The previous O-ring design was based on a circular cross-section.
Fluid Operation General Fluid Operation 8.2.3 Remove Organic Contamination from the Tip Contaminants on the tip may limit AFM resolution. You may use ultraviolet (UV) light to remove contaminants, as follows: 1. Place the fluid cell with installed tip face-up on a clean surface. 2. Position a UV lamp very close (3-5mm) to the fluid cell and irradiate the probe for 15-30 minutes at full intensity. Note: Washing probes in 1-5% SDS (Sodium Dodecyl Sulfate) is also effective. 8.2.
Fluid Operation General Fluid Operation Figure 8.2b Load Probe into Fluid Cell Probe Wire Clip Pocket Fluid Cell (Bottom) 8.2.5 Sample Mounting Secure a sample support (e.g., mica or a glass cover slip) to a magnetic stainless steel sample puck. Supports may be secured to the puck with epoxy. Select epoxy as follows: • For non-critical applications, use Devcon 2-Ton Epoxy or 5-Minute Epoxy.
Fluid Operation General Fluid Operation 1. Install the protective O-ring into the fluid cell. Insert the O-ring into the recessed groove in the underside of the fluid cell. The O-ring slides up into the recessed groove. 2. Install the sample or sample support in the fluid cell. 3. Install the fluid cell in the AFM head, and tighten the clamp to hold the fluid cell in place, making certain that the O-ring positions properly between the sample and fluid cell.
Fluid Operation General Fluid Operation Note: To minimize the risk of fluid leakage, introduce fluid to the fluid cell under vacuum using the following technique: • Attach a piece of silicone tubing to one of the fluid ports using a male Luer fitting. Place the free end of the tubing into a beaker containing the buffer. • Attach a piece of silicone tubing to the other fluid port using a male Luer fitting. • Fill the fluid cell with fluid by withdrawing the plunger on the syringe.
Fluid Operation General Fluid Operation Figure 8.2d Stainless Steel Sample Puck with Teflon Cover Mica Aqueous Sample Teflon Stainless Steel Sample Puck You may load the sample on the support now, or you may inject it when the fluid cell is installed inside the AFM head. Two variations of this method are possible: starting with a dry sample and starting with a sample in solution. 1. Complete the following if starting with a dry sample: a. Attach the sample support (e.g., mica) to a puck. b.
Fluid Operation General Fluid Operation Figure 8.2f Imaging a Sample Covered by a Drop of Fluid Fluid Probe Holder Meniscus Scanner 4134 Sample Puck 2. Complete the following if starting with a sample in solution: a. Incubate 30-40µl of your sample on the support mounted on the puck (the liquid should form a small dome over the support). During this incubation the sample should adhere to the support (e.g., mica). b. Install the sample support on the AFM scanner. c.
Fluid Operation General Fluid Operation 8.2.7 Adjust the Detector Offsets and Setpoint (Contact Mode) Adjust the detector mirror adjustment screws: • In Contact Mode (i.e., Other Controls > Microscope mode set to Contact and Feedback Controls > SPM Feedback set to Deflection), to achieve a vertical deflection signal of roughly -1.0V. Set the Feedback Controls > Deflection Setpoint to 0V to begin.
Fluid Operation General Fluid Operation 2. To avoid sample damage, reduce the Deflection Setpoint as low as possible: a. Stop when the tip pulls off the surface and the Z Center Position on the display monitor jumps to Limit (-220V). 3. Increase the setpoint until the tip begins to touch the surface again and an image appears. • As an alternative, use the Force Calibration command to select the setpoint and estimate the contact force (see Chapter 11).
Fluid Operation TappingMode in Fluids 8.3 TappingMode in Fluids Operation of TappingMode in fluid provides the same advantages of TappingMode in air, with the additional ability to image samples under native liquid conditions. In fluid TappingMode, the probe is oscillated so that it only intermittently contacts the sample surface. This can reduce or eliminate lateral forces that can damage soft or fragile samples in Contact Mode.
Fluid Operation TappingMode in Fluids Figure 8.3a A 100µm, Narrow-legged, Si3N4 Cantilever Fluid Tune Curve • Manually adjust the Zoom in and Offset functions above the Cantilever Tune display. Note: If the expected peak does not appear in the spectrum, choose another peak, engage on the surface and disengage immediately. With the tip closer to the surface, the peak at 8 to 9 kHz appears. Adjust the Drive Amplitude until a desired probe RMS amplitude is obtained. • An RMS amplitude of 0.
Fluid Operation TappingMode in Fluids • Adjust and optimize these settings for each imaging condition and sample. 6. Center the laser spot on the photodiode detector. • Adjust the photodiode until deflection is roughly zero. • The deflection signal can drift when the probe is first in fluid, so it is best to adjust just prior to engaging. 7. Click the Engage icon to bring the tip into tapping range.
Fluid Operation TappingMode in Fluids Note: The slope of the Force Cal curve during probe interaction with the sample surface is defined as the sensitivity of the fluid TappingMode measurement. In general, higher sensitivity results in better image quality. If the sensitivity is poor, check the mounting of the sample and fluid cell. 8.3.3 Optimizing Image Quality Adjust the setpoint by monitoring image quality, as follows: 1. Select an appropriate Scan size.
Fluid Operation Troubleshooting Tips 8.4 Troubleshooting Tips 8.4.1 Cantilever Tune Plot Looks Poor: Loose Probetip The Cantilever Tune plot can be used as a diagnostic tool. Become familiar with its characteristics when good images are obtained. If the plot looks substantially different from previous successful experiments, there may be a problem with the fluid cell. For example, the probe may be loose in its holder. Check the clip which holds the probe in place, and verify the probe is not loose.
Fluid Operation Troubleshooting Tips b. While the tip is kept in gentle contact with the substrate surface, add the sample substance to be imaged and allow it to diffuse/settle onto the substrate. c. After a diffusion/settling period has lapsed, quickly lift the tip from the substrate surface. d. Switch Other Controls > Microscope mode to Tapping and image the sample before it becomes contaminated. Dull Tip Change to a new probe.
Fluid Operation Troubleshooting Tips lateral stress. This also forms a fluid-tight seal between the O-ring and sample. However, some solvents (i.e., nonpolar organic solvents) may dissolve some of the lubricant into the fluid. • Substitute an alternative for the O-ring: • Replace the O-ring with a slice of thin-walled glass, plastic or stainless steel tubing.
Fluid Operation General Notes on Sample Binding 8.5 General Notes on Sample Binding Samples for AFM imaging should be immobilized on a rigid substrate. Macroscopic samples (biomaterials, crystals, polymer membranes, etc.) can be attached directly to a stainless steel sample disk with an adhesive. Dissolved or suspended samples like cells, proteins, DNA, etc. are usually bound to a flat substrate like mica or glass, for example.
Fluid Operation Lysozyme on Mica—A Model Procedure for Protein Binding 8.6 Lysozyme on Mica—A Model Procedure for Protein Binding 8.6.1 Protein Binding Theory All proteins contain free amino groups that become positively charged at sufficiently low pH. If sufficient free amino groups are located on the outside surface of the protein, then the protein will bind to a negatively charged mica surface.
Fluid Operation Lysozyme on Mica—A Model Procedure for Protein Binding • TappingMode Fluid Cell, Model MMTFC • Cantilevers (Oxide-Sharpened Silicon Nitride tips, Model NP-S, work well) • Source of filtered (0.2 µm), compressed air or dry nitrogen • UV lamp, high-intensity; Oriel Mod. 6035 pencil-style spectral calibration lamp or equivalent (optional for cantilever cleaning).
Fluid Operation Lysozyme on Mica—A Model Procedure for Protein Binding 9. After the fluid cell has been flushed with buffer solution, reclamp the drain line. This is important for low-noise, low drift imaging. The sample is now ready for TappingMode imaging. A good TappingMode image of lysozyme protein on mica is shown in Figure 8.6b Figure 8.6b TappingMode image of lysozyme in buffer solution using above sample preparation (Scan size = 500nm).
Fluid Operation Binding DNA to Mica 8.7 Binding DNA to Mica 8.7.1 DNA Binding Theory DNA and mica are both negatively charged, and so it is necessary to modify the mica surface or the DNA counter ion to allow binding. The counterion method is done by adsorbing the DNA onto the mica in the presence of a divalent (+2 charged) ion, like Ni+2. The divalent ion will serve as a counterion on the negatively charged DNA backbone and will also provide additional charge to bind the mica.
Fluid Operation Binding DNA to Mica 1. Obtain the required materials: • Mica substrates • DNA: BlueScript II SK9(+) double stranded plasmid DNA, 2961 base pairs, 1mg/ml in 10mM Tris, 1mM ethylenediaminetetraacetic acid (EDTA) from Stratagene, La Jolla, CA. • Buffer solution: 10 mM HEPES and 5 mM NiCl2 pH 7.6 (for loose binding and air imaging), or NiCl2 (for tight binding and fluid imaging) 2. Dilute DNA in buffer solution to a final concentration of 2.5 ng/µl. 3.
Chapter 9 Scanning Tunneling Microscopy (STM) STM STM relies on “tunneling current” between the probe and the sample to sense the topography of the sample. The STM probe, a sharp metal tip (in the best case, atomically sharp), is positioned a few atomic diameters above a conducting sample which is electrically biased with respect to the tip. At a distance under 1 nanometer (0.001µm), a tunneling current will flow from sample to tip.
Scanning Tunneling Microscopy (STM) STM Introduction • Low-Current STM: Section 9.5 • Description: Section 9.5.1 • Hardware Description: Section 9.5.2 • Precautions: Section 9.5.3 • Installation: Section 9.5.4 • Operation: Section 9.5.5 • Servicing the Converter: Section 9.5.6 • Etching Tungsten Tips: Section 9.6 • Procedure: Section 9.6.1 9.1 STM Introduction 9.1.1 Overview of STM STM relies on a precise scanning technique to produce very high-resolution, three-dimensional images of sample surfaces.
Scanning Tunneling Microscopy (STM) STM Introduction 9.1.2 STM Hardware Some individual STM components are described below: STM Converter head and tipholder—To perform STM, you need to add a MultiMode STM convertor head (see Figure 9.1a). The STM converter head (so-called because it “converts” the MultiMode to a scanning tunneling microscope) consists of a rigid ring bisected by a solid support for the tipholder.
Scanning Tunneling Microscopy (STM) STM Introduction 9.1.3 Sample Surface Samples to be imaged with a scanning tunneling microscope must conduct electricity. In many cases nonconductive samples can be coated with a thin layer of a conductive material to facilitate imaging. The sample surface must be conductive enough to allow a few nanoamps of current to flow from the bias voltage source to the area to be scanned.
Scanning Tunneling Microscopy (STM) Basic STM Operation 9.2 Basic STM Operation 9.2.1 System Setup This section explains how to use the NanoScope to image a conductive sample. Select the STM option in the software Select Microscope > Profile > STM or Other Controls panel > Microscope mode > STM. Prepare the sample The STM bias voltage is supplied to the sample through the top of the scanner. The sample surface must be electrically connected to the scanner end cap.
Scanning Tunneling Microscopy (STM) Basic STM Operation Set Initial Scan Parameters 1. “Show All Items”: Before changing any parameters, you should display all of the available parameters. If you cannot view a parameter in a panel, you might need to enable this parameter. a. Click the “minus box” items. in the upper left corner of the panel, and click Show all Figure 9.2a Select Show All Items a.Click here 045 b.Select this b. Ensure there is a “X” in the check box to the left of all parameters.
Scanning Tunneling Microscopy (STM) Spectroscopy with the STM 2. Prior to engaging the microscope it is necessary to set the Bias voltage and Current Setpoint. A good typical Current Setpoint is 1-2nA. A good recommended Bias voltage is 20-50mv for highly conductive samples like graphite or gold. Try using Bias voltages of 100-500mv for less conductive materials. Usually if Scan Size is greater than 1µm, altering the values of Current and Bias voltage do little.
Scanning Tunneling Microscopy (STM) Spectroscopy with the STM 9.3.2 Operation of STS In the following sections, the operation of the spectroscopic functions of the NanoScope III STM will be discussed. Additional information can be obtained from the Command Reference Manual. STS Plot There are several items that you should be aware of when using the NanoScope to acquire spectroscopic plots with the STS Plot commands.
Scanning Tunneling Microscopy (STM) Troubleshooting for STM 9.4 Troubleshooting for STM This section addresses errors or malfunctions encountered during the operation of the MultiMode as an STM. See Chapter 15 in this manual for additional troubleshooting tips. 9.4.1 Head and Microscope-related Problems This section deals with problems related to the scanners or the microscope. If a problem exists with a scanner, try a second one under the same conditions, if possible.
Scanning Tunneling Microscopy (STM) Low-Current STM Head/Tip Problem Check sample conductivity Troubleshooting Tip There are two problems associated with sample conductivity: 1). The bulk conductivity of the sample may make it difficult to image. If the resistance of the sample is greater than 1KΩ/cm, higher bias voltages should be tried. If the resistance is greater than 1MΩ, bias voltages of 100mV or more should be used.
Scanning Tunneling Microscopy (STM) Low-Current STM 9.5.2 Hardware Description The Low Current STM head, which allows STM measurements with Itun in the pA range is constructed for operation with our MultiMode and AFM bases. Low-current STM operation also requires the Picoamp Boost Box, which is installed between the control unit or extender box and the MultiMode or AFM base. Figure 9.5a Low-Current Converter components: MultiMode head and Picoamp Boost Box.
Scanning Tunneling Microscopy (STM) Low-Current STM 3. Good grounding is essential for low-noise performance. A good contact between the SPM base and the metallic cover (can) included with the low current head is needed to reduce the electrical noise level. A simple grounding kit is included with the converter which includes a length of wire and connecting lugs. Make certain that the can cover and SPM base are electrically connected by the wire and that the can cover is in place.
Scanning Tunneling Microscopy (STM) Low-Current STM MultiMode SPM IMPORTANT! If you are installing on a MultiMode SPM equipped with the Basic Extender Module, you must install the Picoamp Boost box with the jumpers inside set for extended. A label on the outside of the Boost box indicates whether it was set for standard (Model MMSTMLC) or Extender (Model MMSTMLCE) at the factory. If you are not certain which base your MultiMode has, contact Veeco for guidance. 1. Turn off all power to the SPM controller.
Scanning Tunneling Microscopy (STM) Low-Current STM Preamp Setting Current Sensitivity Setting 1010 0.1nA/V 1011 0.01nA/V 9.5.5 Operation The operation of the low-current STM head is typically checked in the atomic-scale imaging of graphite and the large-scale imaging of a gold-coated grating. The atomic-lattice of graphite is well resolved in the images obtained with Itun in the 2-20pA and Vbias in the 20-100mV range.
Scanning Tunneling Microscopy (STM) Low-Current STM Figure 9.5b STM current and height images of HOPG surface. Scan size = 6.0nm, Itun = 1.6pA, Vbias = 29mV. Figure 9.5c STM current image of layered crystal α-RuCl3. Scan size = 4.48nm, Itun = 1.5pA, Vbias = 42mV. Rev.
Scanning Tunneling Microscopy (STM) Low-Current STM Figure 9.5d STM height image of alkanethiol layer on Au (111) substrate. Scan size = 178.5nm, Itun = 2pA, Vbias = 1V. (Courtesy of Dr. I. Tuzov, NCSU) Figure 9.5e Molecular-scale STM current image of alkanethiol layer on Au (111) substrate. Scan size = 10.0nm, Itun = 13pA, Vbias = 1V. (Courtesy of Dr. I. Tuzov, NCSU) 9.5.
Scanning Tunneling Microscopy (STM) Low-Current STM 2. Use the 0.050" allen wrench, included in the converter kit, to loosen the two retaining screws which secure the head’s cover. It is not necessary to remove the screws. Loosen these two screws. 3. Pull the cover straight up and off to expose the PC board and electronics. It will appear as shown below. Op-amp Precision resistor and capacitor.
Scanning Tunneling Microscopy (STM) Etching Tungsten Tips Metal tab at “10:00” position. To remove, pull straight up. To install, push straight down. (Do not bend leads) 6. Verify that each of the op-amp’s wire leads is properly aligned with the appropriate hole, then press the op-amp gently into its socket. Do not bend wire leads. 7. Replace the metal cover on the head. Retighten retaining screws to secure. 9.6 Etching Tungsten Tips You can purchase tungsten tips from Veeco or make them yourself.
Scanning Tunneling Microscopy (STM) Etching Tungsten Tips 9.6.1 Procedure 1. Mix a 5% (by weight) solution of Sodium Nitrite in water. 2. Pour ≈ 40ml of the Sodium Nitrite solution into a beaker. 3. Pour ≈ 40ml of WD 40 into a beaker. 4. Construct an electrode out of the platinum wire and insert it into the beaker. 5. Adjust the variac for 30V, and with it Off, connect one output to the platinum electrode. 6. Cut 10 to 12 pieces of tungsten wire ≈ 1.25cm long.
Lateral Force Mode Chapter 10 Lateral Force Mode The MultiMode SPM is capable of measuring frictional forces on the surfaces of samples using a special measurement known as lateral force microscopy (LFM). The name derives from the fact that cantilevers scanning laterally (perpendicular to their lengths) are torqued more as they transit high-friction sites; low-friction sites tend to torque cantilevers less.
Lateral Force Mode Basic LFM Operation 10.1 Basic LFM Operation 1. Set up and run the system in Contact mode as described in Chapter 6, assigning the Channel 1 image to Data Type: Height and the Channel 2 image to Data Type: Friction. Set the Scan angle to 90.00. 2. Optimize the scan parameters in AFM mode for Channel 1. 3. For Channel 2, set Line direction to Trace. This will place high lateral forces on the top of the color bar and low lateral forces on the bottom of the color bar.
Lateral Force Mode Advanced LFM Operation 10.2 Advanced LFM Operation 10.2.1 Scan Direction The cantilever is most susceptible to frictional effects when the scan direction runs perpendicular to the major axis of the cantilever as shown in Figure 10.2a. The Scan angle parameter in the Scan Controls panel must be set to 90° or 270° to produce this scan direction. Figure 10.
Lateral Force Mode Advanced LFM Operation 10.2.2 Tip selection The analog-to-digital converter on the auxiliary input channel which is used for LFM data has a maximum input range of ±10V. This, and the anticipated interaction between tip and sample define the selection of the cantilever to be used for the measurement. The 200µm cantilever with wide legs provides a good starting point for frictional measurements. It is flexible enough to provide reasonable signal levels on samples with moderate friction.
Lateral Force Mode Advanced LFM Operation Table 10.
Lateral Force Mode Advanced LFM Operation 10.2.5 Using TMR Voltage to Measure Friction The signal called TMR (Trace minus Retrace) in the scope mode display measures the voltage difference between the Trace and the Retrace scan directions. In the case of LFM data, this directly corresponds to the amount of total tip twist that occurs as the tip scans back and forth across the sample. It is common to study the frictional differences between two different samples.
Lateral Force Mode Advanced LFM Operation 10.2.7 Height Artifacts in the Signal LFM is subject to height artifacts due to coupling with surface topography. Delay in the feedback loop causes the tip to momentarily twist as it climbs up an edge. This will be visible in the friction data if it’s severe enough. To distinguish real friction data from height artifacts, remember that friction causes the cantilever to twist in the opposite direction as it travels.
Chapter 11 Force Imaging Force plots are used to measure tip-sample interactions and determine optimal setpoints. More recently, microscopists have begun to collect force measurements across entire surfaces to reveal new information about the sample. This area of SPM promises to open new chapters in materials science, biology and other investigative areas. Specifically, this chapter details the following topics: • Force Plots–An Analogy: Section 11.1 • Force Calibration Mode: Section 11.
Force Imaging • Force Calibration (TappingMode): Section 11.5 • Force Plots: Section 11.5.1 • Obtaining a Force Plot (TappingMode): Section 11.5.2 • High Contact Force: Section 11.5.3 • Tip Selection: Section 11.5.4 • Force Modulation: Section 11.6 • Introduction: Section 11.6.1 • Selecting a Force Modulation Tip: Section 11.6.2 • Operating Principle: Section 11.6.3 • Force Modulation Procedure: Section 11.6.4 • Notes About Artifacts: Section 11.6.5 • Force Modulation with ‘Negative LiftMode’: Section 11.
Force Imaging Force Plots–An Analogy 11.1 Force Plots–An Analogy A force plot is an observation of tip-sample interactions which yields information regarding the sample and tip. By way of analogy, suppose a materials researcher must determine how powerful two different types of magnets are. One magnet is made of iron, the other is a stronger, so-called “rare earth” magnet. A simple way of measuring each magnet’s power would be to determine its pull upon a steel plate.
Force Imaging Force Calibration Mode First, magnet #1 is weaker, attaching to the steel plate with 7N of pulling force at 6cm, and magnet #2 is stronger, attaching at 7cm with 10N. Figure 11.1b Pulling Forces Graph kg +1 N 10 0 Magnet #2 -5 -10 0 Magnet #1 -1 2 3 4 5 6 7 8 9 10 11 Height above steel plate (cm) This oversimplified model depicts activity between SPM tips and various materials. In reality, SPM force plots reveal far more.
Force Imaging Force Calibration Mode As a result of the applied voltage, the sample moves up and down as shown in Figure 11.2c. The Z scan start parameter sets the offset of the piezo travel, while the Ramp size parameter defines the total travel distance of the piezo. Therefore, the maximum travel distance is obtained by setting the Z scan start to +220V, with the Scan size set to 440V. Figure 11.2b represents a tip-sample-piezo relationship on a MultiMode system.
Force Imaging Force Calibration Mode 11.2.1 Example Force Plot Figure 11.2c Tip-Sample Interaction During a Force Plot 1 2 3 6 4 5 7 Let’s begin with the simplest of SPM force plots: a contact AFM force plot using a silicon nitride tip. Because of the lower spring constant of silicon nitride probes, they are more sensitive to attractive and repulsive forces. A force plot in contact AFM is shown below (see also Figure 11.2c). Figure 11.2c compares portions of the force curve shown in Figure 11.
Force Imaging Force Calibration Mode Controls panel defines the rate at which the piezo completes an extension-retraction cycle (and therefore the rate at which new curves are displayed). 11.2.2 Contact AFM Force Plots 1 2 Up Piezo extension Piezo retraction 4 2 Down Cantilever deflection Figure 11.2d Anatomy of a Force Curve 3 6 1 7 5 Piezo extends; tip descends. No contact with surface yet. Tip is pulled down by attractive forces near surface.
Force Imaging Force Calibration Mode The cantilever’s deflection is plotted on the vertical axis of the graph: when the cantilever is deflected downward, it is plotted on the graph’s downward vertical; when the cantilever is deflected upward, it is plotted on the graph’s upward vertical. The graph reveals at least two very important things: • Sample-tip attraction—As the tip approaches the sample, various attractive forces reach out and “grab” the tip.
Force Imaging Force Calibration Control Panels and Menus 11.3 Force Calibration Control Panels and Menus The Force Calibration Control window (see Figure 11.3a) manipulates the microscope in Force Calibration mode. The parameters control the rate, start position and amplitude of the triangle wave applied to the Z piezo. You can also adjust the Setpoint value of the cantilever deflection voltage used in the feedback loop during imaging. The Capture button stores the force curve for Offline viewing.
Force Imaging Force Calibration Control Panels and Menus 11.3.1 Main Controls (Ramp Controls) Ramp Channel (Advanced Only) This parameter specifies the channel you will ramp. To collect force plots, this parameter should be set to Z. For IV curves, Bias is typically selected. Ramp Size As shown in Figure 11.2a, this parameter defines the amplitude of the triangular waveform applied to the Z piezo. The units of this item are volts or nanometers, depending on the setting of the Units parameter.
Force Imaging Force Calibration Control Panels and Menus Number of Samples This parameter defines the number of data points captured during each extend and retract operation of the Z piezo during Force Calibration. This parameter does not affect the number of samples used in Image Mode. Average Count (Advanced Mode Only) This parameter defines the number of Force Calibration scans taken to average in the display of the Force Calibration graph. Set to 1 unless the user needs to reduce noise.
Force Imaging Force Calibration Control Panels and Menus 11.3.3 Channel 1, 2, 3 Panels Data Type This parameter allows you to select the type of data you want to display on the vertical axis. Data Scale This parameter sets the vertical scale in the force plot. Increasing this parameter expands the range of the display about the centerline causing more of the force curve to fall on the graph. Initially, set this parameter to its maximum value, then gradually reduce.
Force Imaging Force Calibration Control Panels and Menus 11.3.4 Feedback Controls Panel All of the parameters in the Feedback Controls panel also affect Image mode. Deflection Setpoint (Contact Mode) By changing the deflection setpoint, you can adjust the cantilever deflection voltage maintained by the feedback loop in Image mode. This parameter defines the center of the range of Cantilever Deflection Voltages that can be collected.
Force Imaging Force Calibration Control Panels and Menus 11.3.5 Scan Mode Panel (Advanced Mode Only) Trigger Mode The Scan Mode panel allows you to use various triggers when obtaining Force Plot and Force Volume plots. The idea of triggering simple: it limits the total amount of force exerted by the tip upon the sample. Depending upon which trigger you use and how it is set, you may operate the trigger independent of drift (Relative) or at some arbitrarily fixed point (Absolute). Figure 11.
Force Imaging Force Calibration Control Panels and Menus Trigger Threshold This parameter as well as the Trigger Direction and Trigger Mode define the level at which trigger occurs.
Force Imaging Force Calibration Control Panels and Menus Ramp Delay This parameter sets the amount of time to wait with the piezo extended before retracting. Reverse Delay This parameter sets a delay to occur each time the piezo is retracted while continuously ramping. Auto Offset If the trigger is not achieved within a range twice the ramp size, then the retract will begin without reaching the trigger voltage.
Force Imaging Force Calibration (Contact Mode AFM) Motor The Motor menu allows you to withdraw or manually control the tip position using the stepper motor. Selecting Step Motor opens a dialog box containing the following buttons: • Tip Up: This command moves the tip up by the SPM step size displayed inside the window. • Tip Down: This command moves the tip down by the SPM step size displayed inside the window. 11.4 Force Calibration (Contact Mode AFM) 11.4.1 Obtaining a Good Force Curve Figure 11.
Force Imaging Force Calibration (Contact Mode AFM) 3. In the Channel 1 panel select Deflection as the Data Type. 4. Maximize the Data Scale parameter. 5. Adjust the Ramp size parameter to about 1µm. 6. If the tip does not reach the sample surface (for example, see Figure 11.4a, between points 2 and 3), slowly increase the Z scan start value. 7. As the Z scan start increases, the traces on the force curve move to the right. 8. Adjust the Setpoint parameter.
Force Imaging Force Calibration (Contact Mode AFM) Figure 11.4b False Engagement (G Scanner) Retracting Extending Possible False Engage Points Tip Deflection 0.48 V/div Setpoint Z Position - 9.27 V/div Motor Control Motor Control > Tip Up and Tip Down buttons provide coarse adjustment of Z center voltage. With these buttons the SPM head moves vertically. The feedback loop causes the Z piezo to adjust to compensate for the head movement. If you use Tip Up, the Z piezo extends.
Force Imaging Force Calibration (Contact Mode AFM) 11.4.3 Advanced Techniques Sensitivity Determination The Deflection Sensitivity allows conversion from the raw photodiode signal (in Volts) to deflection of the cantilever (in nm), and is normally set from the Force Calibration mode. The sensitivity must be calibrated before accurate deflection data can be obtained. Sensitivity is equal to the inverse of the slope of the force curve while the cantilever is in contact with a hard sample surface.
Force Imaging Force Calibration (Contact Mode AFM) Note: Deflection Sensitivity can be expressed in terms of the photodiode voltage versus the distance traveled by the piezo, or the photodiode voltage versus the voltage applied to the piezo, depending on the setting of the Units parameter. Force Minimization Force Calibration mode allows minimization of the contact force of the cantilever on the sample surface.
Force Imaging Force Calibration (Contact Mode AFM) Calculating Contact Force The force curve clearly shows the relationship between the setpoint and the deflection of the cantilever. Because the setpoint defines the value of the deflection signal maintained by the feedback loop, the force curve can be used to calculate the contact force of the tip on the sample if the spring-constant, k , of the cantilever is known.
Force Imaging Force Calibration (Contact Mode AFM) Force calculations are not as straightforward on images captured with the Data type set to Deflection. When collecting deflection data, the feedback gains are ideally set low so the sample stays at a nearly constant position relative to the cantilever holder. In this case, the cantilever deflection (and therefore the force applied to the sample) varies as features on the surface are encountered.
Force Imaging Force Calibration (Contact Mode AFM) 11.4.4 Interpreting Force Curves An examination of force curves can prove useful in determining adhesion, hardness, and elastic characteristics of samples. The examples in Figure 11.4e represent some of the general variations in force curves. For more information regarding force imaging, refer to Veeco’s application note Probing Nano-Scale Forces with the Atomic Force Microscope. Figure 11.
Force Imaging Force Calibration (TappingMode) 11.5 Force Calibration (TappingMode) CAUTION: Because TappingMode cantilevers are relatively stiff, Force Mode can potentially damage the tip and/or surface. Before using Force Calibration, read and understand the following section. Force Mode allows the imaging of forces between the tip and surface, including chemical bonds, electrostatic forces, surface tension and magnetic forces.
Force Imaging Force Calibration (TappingMode) Figure 11.5a Piezo Extension Versus RMS Amplitude and Deflection Piezo extension 1 Piezo retraction 5 Tip is clear of the surface 2 z - 10.00nm/div 4 047 3 z - 10.00nm/div Figure 11.5a illustrates a two-channel TappingMode force plot. The vertical axes of the graphs represent the amplitude (top) and TM deflection signal (bottom) of the cantilever. The position of the Z piezo plots along the horizontal axis.
Force Imaging Force Calibration (TappingMode) When the piezo turns around and begins to retract, the oscillation amplitude of the cantilever increases until the tip is free of the surface, leveling off at the free-air amplitude (point 5). Channel 2 (bottom) in Figure 11.5a plots average cantilever deflection (TM deflection) versus piezo extension. The deflection signal is low-pass filtered to eliminate the high-frequency TappingMode oscillation.
Force Imaging Force Calibration (TappingMode) 5. Set the Main Controls and Channel 1 panel parameters to the settings shown in Figure 11.5b. Note: The Sensitivity value shown in Figure 11.5b may differ from yours. 037 Figure 11.5b TappingMode Force Plot Parameter Settings (Force Calibrate) 6. Set the Data type parameter to Amplitude under the Channel 1 panel. 7. Adjust the Z scan start parameter to obtain a satisfactory force plot using the left-right arrow keys.
Force Imaging Force Calibration (TappingMode) 11.5.3 High Contact Force Figure 11.5c shows a curve produced when the tip pushes too far into the sample. The flat portion on the left side of the amplitude curve in Figure 11.5c occurs because the tip is so close to the surface that it no longer vibrates. As the piezo extends the tip further, the amplitude of vibration does not change because the tip is always in contact with the sample surface.
Force Imaging Force Modulation 11.6 Force Modulation 11.6.1 Introduction This section describes the operation of force modulation mode, which you can use to image local sample stiffness or elasticity. This method is useful for imaging composite materials or soft samples on hard substrates where you can obtain contrast between regions of different elasticity. This section assumes knowledge of operation of Contact Mode AFM in air (see Chapter 6).
Force Imaging Force Modulation 11.6.2 Selecting a Force Modulation Tip The key consideration when selecting a force modulation cantilever is its spring constant. Ideally, the cantilever must have a spring constant which compliments the pliancy of the two contrasting materials (or close to the pliancy of one, but not the other). This way, the tip indents into one material more than the other providing good force modulation image contrast.
Force Imaging Force Modulation 11.6.3 Operating Principle Force modulation mode is very similar to Contact Mode AFM. The NanoScope system scans the cantilever over the sample surface while trying to keep the cantilever deflection constant. The deflection setpoint determines the average deflection during operation. In addition, the cantilever is oscillated up and down by a piezoelectric bimorph in the tipholder so that the tip indents slightly into the sample surface as it is scanned across the surface.
Force Imaging Force Modulation 8. Find the Bimorph Resonant Frequency: The cantilever is oscillated by a small piezoelectric bimorph mounted in the cantilever holder. For Force Modulation, oscillate the bimorph at or near its resonant frequency. The bimorph resonance frequency is usually the largest peak in the 5-30kHz range. This ensures the cantilever moves with sufficient amplitude to produce elasticity contrast. Note: You need to find the bimorph’s resonant frequency only once.
Force Imaging Force Modulation Figure 11.6d Typical Frequency Sweep Plot Peaks due to bimorph Note: f. Peaks due to cantilever The large drive amplitude is necessary because peaks are smaller than normally seen during TappingMode operation. This is due to the cantilever not at resonance; therefore, its motion is mostly vertical. Vertical motion is not amplified by the beam deflection detection technique which is sensitive primarily to changes in cantilever angle.
Force Imaging Force Modulation n. Adjust the Drive amplitude so the maximum response amplitude is about 1V. Recenter the peak if necessary. 020 Figure 11.6e Correctly Tuned Force Modulation Frequency Note: You may also change the Drive Frequency by clicking on the Drive Frequency parameter on the control monitor’s Feedback Controls panel, and entering a new value. Note: Bimorph resonance should be between 5 kHz and 30 kHz.
Force Imaging Force Modulation 14. Adjust the Integral Gain, Proportional Gain, Setpoint, and Scan Speed to obtain a good topography (Height) image. For force modulation operation, set the Integral Gain and Proportional Gain to values of 1-10 and set the Setpoint as low as possible using the cursor keys (or by typing in new Setpoint values) until the cantilever pulls off the surface and the Zcenter voltage jumps to -220V. 15.
Force Imaging Force Modulation 5. The value of the Drive amplitude may also affect the Contact Mode AFM image, causing the system to go into unwanted oscillations. If the Drive amplitude changes by a large amount, readjust the Integral gain and Proportional gain. Set the gains as high as possible to track the sample topography, but not so high that they cause oscillation due to the bimorph oscillation.
Force Imaging Force Modulation Figure 11.6f Friction on Force Modulation Images 1516 tip moves down and left substrate moves down Effect of friction on force modulation images Tip Shape The amount of indentation into a surface for a given applied force depends on the shape of the cantilever tip. For the same Drive Amplitude a sharper tip indents deeper than a dull tip.
Force Imaging Force Modulation with ‘Negative LiftMode’ 11.7 Force Modulation with ‘Negative LiftMode’ A new form of force modulation imaging utilizing TappingMode and LiftMode operation known as “Negative LiftMode,” allows imaging of certain materials previously not visible with Contact Mode AFM force modulation. This method is especially suited for softer materials, yielding higher resolution.
Force Imaging Force Modulation with ‘Negative LiftMode’ 11.7.2 Obtain a TappingMode Image While negative LiftMode force modulation data is imaged using Channel 2, height data is obtained using TappingMode on Channel 1. You must obtain a satisfactory TappingMode image to generate good data. 1. Verify that the Interleave mode parameter on the Interleave Controls panel is Disabled. 2. Verify that the AFM mode parameter in the Other Controls panel is set to Tapping. 3.
Force Imaging Force Volume Note: If the Lift scan height is too large, the interleave may be tapping, and therefore not in the continuous contact required for force modulation. 4. Adjust the interleaved Drive amplitude and Lift scan height until the force modulation image is optimized. This may require some experimentation. Note: If you see a lot of contrast in the amplitude image before reaching the surface, try reducing the Integral and Proportional gains in the Feedback Controls panel.
Chapter 12 Interleave Scanning and LiftMode The following sections are included in this chapter: • Preface: Interleave Scanning & LiftMode: Section 12.1 • Interleave Mode Description: Section 12.2 • Lift Mode Description: Section 12.3 • Operation of Interleave Scanning / Lift Mode: Section 12.4 • Use of LiftMode with TappingMode: Section 12.5 • Main Drive Amplitude and Frequency selection: Section 12.5.1 • Setpoint Selection: Section 12.5.2 • Interleave Drive Amplitude and Frequency Selection: Section 12.
Interleave Scanning and LiftMode Preface: Interleave Scanning & LiftMode 12.1 Preface: Interleave Scanning & LiftMode Interleave is an advanced feature of NanoScope software which allows the simultaneous acquisition of two data types. Enabling Interleave alters the scan pattern of the piezo. After each main scan line trace and retrace (in which topography is typically measured), a second (Interleave) trace and retrace is made with data acquired to produce an image concurrently with the main scan.
Interleave Scanning and LiftMode Interleave Mode Description 12.2 Interleave Mode Description Enabling Interleave changes the scan pattern of the tip relative to the imaged area. With Interleave mode disabled, the tip scans back and forth in the fast scan direction while slowly moving in the orthogonal direction as shown on the left of Figure 12.2a. This is the standard scan pattern of the NanoScope III. Figure 12.
Interleave Scanning and LiftMode Lift Mode Description 12.3 Lift Mode Description With the Interleave scan option set to Lift, the motion of the tip during the Interleave trace and retrace is as shown in Figure 12.3a. Figure 12.3a LiftMode Profiles Lift Trace Main Trace (Height Data) Lift Start Height Lift Scan Height Lift Scan Height The tip first moves to the Lift start height, then to the Lift scan height. A large Lift start height can be used to pull the tip from the surface and eliminate sticking.
Interleave Scanning and LiftMode Operation of Interleave Scanning / Lift Mode Note that certain constraints are imposed: scan sizes, offsets, angles, and rates and numbers of samples per scan line are the same for the main and interleave data, and the imaging context (contact, TappingMode, or force modulation) must also match. 3.
Interleave Scanning and LiftMode Use of LiftMode with TappingMode 12.5 Use of LiftMode with TappingMode There are additional considerations when using LiftMode with TappingMode. 12.5.1 Main Drive Amplitude and Frequency selection As usual, these parameters are set in Cantilever Tune before engaging. It is helpful to keep in mind the measurements to be done in LiftMode when setting these values.
Interleave Scanning and LiftMode Use of LiftMode with TappingMode 12.5.3 Interleave Drive Amplitude and Frequency Selection The cantilever drive amplitude can be set differently in the Lift scan as compared to the main scan by toggling the flag on the left of the corresponding Interleave Control to “on” (green) and adjusting the value. This allows the tuning of a measurement in the Lift scan lines without disturbing the topography data acquired during the Main scan lines.
Interleave Scanning and LiftMode Use of LiftMode with TappingMode 12.5.5 Cantilever Oscillation Amplitude The selection of the oscillation amplitude in LiftMode depends on the quantity to be measured. For force gradients which are small in magnitude but occur over relatively large distances (sometimes hundreds of nm, as with magnetic or electric forces), the oscillation amplitude can be large, which for some applications may be beneficial.
Chapter 13 Magnetic Force (MFM) Imaging This chapter describes how to perform Magnetic Force Microscopy (MFM) using the Interleave and LiftMode procedures discussed in Chapter 12. Please review those sections prior to attempting MFM. Best results will be obtained with either the Digital Instruments Veeco Basic Extender Module or the Quadrex Extender Module. These hardware units allows phase detection and frequency modulation for optimal MFM imaging.
Magnetic Force (MFM) Imaging Magnetic Force Imaging Theory 13.1 Magnetic Force Imaging Theory MFM imaging utilizes the Interleave and LiftMode procedures discussed in Chapter 12; users are advised to read appropriate sections prior to attempting MFM imaging. Best results will be obtained with Digital Instruments Quadrex Extender or Basic Extender Modules. These hardware units allow phase detection and frequency modulation for optimal MFM imaging.
Magnetic Force (MFM) Imaging MFM Using Interleave Scanning and LiftMode 034 Figure 13.1b Basic Extender for NanoScope III, IIIa and Quadrex Extender for NanoScope IIIa Controllers (required for MFM phase detection and frequency modulation) Basic Extender Quadrex Extender 13.2 MFM Using Interleave Scanning and LiftMode This section provides instructions for using the LiftMode of Interleave scanning to obtain MFM images.
Magnetic Force (MFM) Imaging MFM Using Interleave Scanning and LiftMode for all TappingMode-capable microscopes in the form of Digital Instruments Veeco’s Basic Extender Electronics Module (Basic Extender) and Quadrex Extender Electronics Module (Quadrex Extender). (Microscopes without an Extender addition cannot utilize phase detection; for more information, contact Veeco.) The design of the NanoScope IV integrates the Quadrex Extender.
Magnetic Force (MFM) Imaging MFM Using Interleave Scanning and LiftMode To correctly track the cantilever phase, the Phase offset parameter must be adjusted. This is automatically done in AutoTune; alternatively, Zero Phase can be selected from the Channel 2 panel. The phase curve should appear as in Figure 13.2a, decreasing with increasing frequency, and crossing the center line (corresponding to a 90° phase lag) at the peak frequency.
Magnetic Force (MFM) Imaging MFM Using Interleave Scanning and LiftMode 036 Figure 13.2c Cantilever Tune for Amplitude Detection Figure 13.2d Shift in amplitude at fixed drive frequency Amplitude ∆F0 Drive Frequency 4. Adjust the Drive Amplitude so that the RMS voltage response of the photodetector is approximately 2V. (Somewhat larger values may be beneficial if using amplitude detection.
Magnetic Force (MFM) Imaging MFM Using Interleave Scanning and LiftMode 9. Engage the AFM and make the necessary adjustments to obtain a good topographical image while displaying height data. Use the highest possible Setpoint to ensure that the tip is contacting the surface only lightly. The image should be similar to the topographic image shown on the left of Figure 13.2e. The surface is fairly flat with lubrication nodules of various sizes. A good image of the nodules indicates that the tip is sharp.
Magnetic Force (MFM) Imaging Installation of the Extender Electronics Modules 13.2.2 Frequency Modulation With the Basic Extender Module, it may be desirable to use frequency modulation. This activates a feedback loop which modulates the Drive Frequency to keep the cantilever’s phase lag at 90 degrees relative to the drive, corresponding to resonance. The frequency Data Type displays the resulting shift in Drive Frequency in Hz, and gives the most direct, quantitative image of force gradients.
Magnetic Force (MFM) Imaging Installation of the Extender Electronics Modules WARNING: Do not insert a conducting object (e.g., screwdriver) into the Extender Electronics while it is engergized. AVERTISSEMENT: WARNUNG: Ne pas insérer d’ objet conducteur (par exemple: un tournevis) dans le boîtier d’extension de electronique (Extender Electronics) quand celuici est sous tension.
Magnetic Force (MFM) Imaging Software Setup Configuration (Basic, Quadrex or NSIV) 13.4 Software Setup Configuration (Basic, Quadrex or NSIV) 1. Select di > Microscope Select to display the Microscope Select dialog box (see Figure 13.4a). 012 Figure 13.4a Microscope Select Dialog Box 2. Click the Edit button to open the Equipment dialog box. 3. Select the appropriate Controller. 4. Select the appropriate Extender. Note: This step is not necessary for NanoScope IV. 5. Click the Ok button when complete.
Magnetic Force (MFM) Imaging Advanced Topics 13.5.2 Saturation in Amplitude Detection If using amplitude detection, the magnetic force image can saturate (appear completely featureless) if the Interleave Drive Amplitude is significantly different than the Drive Amplitude in the main scan. Adjust the Interleave Setpoint to restore the image. (Note that the Interleave Setpoint has no physical effect in LiftMode since there is no surface feedback during the lift pass. 13.5.
Magnetic Force (MFM) Imaging Advanced Topics is usually not beneficial to use Lift scan heights much smaller than the surface roughness. Users are encouraged to experiment for the best images on their samples. The ultimate lateral resolution of MFM is near 20nm. Resolution is affected by properties of the tip, including mechanical sharpness and magnetic structure. When in good condition, magneticallycoated tips routinely give 50nm resolution, and many achieve 30nm or better. Figure 13.
Magnetic Force (MFM) Imaging Advanced Topics In LiftMode, the Interleave Drive Amplitude can often be set to a value larger than in the main scan, thus giving optimal signal-to-noise. In some cases this is beneficial as long as the Drive Amplitude is not increased to the extent that the tip strikes the surface on the low point of its swing. The signatures of tip-sample contact are white and black spots in the image, or, in extreme cases, noisy, high-contrast streaks across the whole image.
Magnetic Force (MFM) Imaging Advanced Topics Setpoint For the most reproducible results, it is best to use a consistent setpoint. In LiftMode, the total tipsample distance htot is the sum of the average tip-sample distance in TappingMode hT, and the lift scan height hlift (see Figure 13.6b). In TappingMode, the average tip-sample distance hT is equal to the oscillation amplitude, which is determined by the setpoint.
Chapter 14 Electric Force (EFM) Imaging The following sections are included in this chapter: • Electric Force Microscopy Overview: Section 14.1 • Electric Field Gradient Imaging Overview: Section 14.1.1 • Surface Potential Imaging Overview: Section 14.1.2 • Electric Field Gradient Detection—Theory: Section 14.2 • Electric Field Gradient Detection—Preparation: Section 14.3 • • Jumper Configurations for systems without the Basic Extender Module: Section 14.3.
Electric Force (EFM) Imaging Electric Force Microscopy Overview 14.1 Electric Force Microscopy Overview Note: If you have an extender electronics module (Basic or Quadrex) or a NanoScope IV, please consult the provided documentation associated with these options, prior to engaging in electric force microscopy. This chapter describes how to perform electric force microscopy (EFM) imaging on a MultiMode SPM system.
Electric Force (EFM) Imaging Electric Force Microscopy Overview Figure 14.1b EFM LiftMode principles 3 2 Force Gradient Scope Data (Interleave scan) 1521 1 Electric Fields 1 2 3 Topographic Scope Data (Main scan) Cantilever measures surface topography on first (main) scan. Cantilever ascends to lift scan height. Cantilever follows stored surface topography at the lift height above sample while responding to electric influences on second (interleave) scan. Figure 14.
Electric Force (EFM) Imaging Electric Field Gradient Detection—Theory 14.1.2 Surface Potential Imaging Overview Surface potential imaging measures the effective surface voltage of the sample by adjusting the voltage on the tip so that it feels a minimum electric force from the sample. (In this state, the voltage on the tip and sample is the same.) Samples for surface potential measurements should have an equivalent surface voltage of less than ±10V, and operation is easiest for voltage ranges of ±5V.
Electric Force (EFM) Imaging Electric Field Gradient Detection—Theory All of the above methods rely on the change in resonant frequency of the cantilever due to vertical force gradients from the sample. Figure 14.2a shows a diagram of how the Basic Extender Module provides the signal enhancement and feedback allowing gradient detection.
Electric Force (EFM) Imaging Electric Field Gradient Detection—Preparation 14.3 Electric Field Gradient Detection—Preparation This section explains how to conduct electric field gradient imaging by applying a voltage to the tip or sample to generate electric fields. Note: If the sample being imaged has a permanent electric field which does not require the external application of voltage, the steps below are not required and you can proceed to Section 14.4.
Electric Force (EFM) Imaging Electric Field Gradient Detection—Preparation Figure 14.3a Diagram of MultiMode baseplate showing location and orientation of jumpers Jumpers, inside baseplate window To er ntroll pe Co dule o c S Nano ender Mo t or Ex 1. Carefully examine the following figures and identify which jumper configuration, if any, is appropriate for your application. 2. Power down the NanoScope III controller and turn off all peripherals.
Electric Force (EFM) Imaging Electric Field Gradient Detection—Preparation 14.3.1 Jumper Configurations for systems without the Basic Extender Module As shipped from the factory, the jumper configuration on a MultiMode SPM without the Basic Extender Module should appear as shown in Figure 14.3h below. Figure 14.3b Normal Jumper Configuration (for systems without the Basic Extender Module).
Electric Force (EFM) Imaging Electric Field Gradient Detection—Preparation Figure 14.3c Jumper configuration for application of voltage to tip (for systems without the Basic Extender Module). Ground Tip Piezo Cap Analog 2 Analog 2 Sample Gain Select Analog 2 To AFM Tip Auxiliary D (to NanoScope III controller) STM Indicates jumpers Rev.
Electric Force (EFM) Imaging Electric Field Gradient Detection—Preparation Voltage Applied to the Sample The jumper configuration in Figure 14.3d connects the Analog 2 signal from the NanoScope III controller (± 12 VDC range) to the sample chuck. Enabling the Analog 2 Voltage Line The “Analog 2” voltage line is normally used by the NanoScope to control the attenuation (1x or 8x) of the main feedback signal. This application of EFM imaging uses the Analog 2 signal for EFM data.
Electric Force (EFM) Imaging Electric Field Gradient Detection—Preparation External Voltage Source Applied to the Tip In some cases, it may be advantageous to use voltages greater than 12 VDC, or to use a pulsed power supply. If an external source of voltage is to be applied to the tip, configure jumpers as shown in Figure 14.3e. Note: In all configurations which apply voltage to the tip, an E-field cantilever holder is required. Contact Veeco for more information. Figure 14.
Electric Force (EFM) Imaging Electric Field Gradient Detection—Preparation External Voltage Source Applied to the Sample In some cases, it may be advantageous to use voltages greater than 12 VDC, or to use a pulsed power supply. If an external source of voltage is to be applied to the sample, configure jumpers as shown in Figure 14.3f. Figure 14.3f Jumper configuration for applying external voltage to sample (for systems without the Basic Extender Module).
Electric Force (EFM) Imaging Electric Field Gradient Detection—Preparation 14.3.2 Jumper Configurations for systems with the Basic Extender Module REMINDER: Power down the microscope and turn off all peripherals. Unplug the NanoScope III control and power cables from the system before attempting to adjust jumper configurations. As shipped from the factory, systems with the Basic Extender option, should have an original baseplate jumper configuration as shown in Figure 14.3g. Figure 14.
Electric Force (EFM) Imaging Electric Field Gradient Detection—Preparation Voltage Applied to the Tip Notice that the jumper configuration in Figure 14.3h connects the Analog 2 signal from the NanoScope III controller (± 12 VDC range) to the tip, and is exactly the same as the jumper configuration shown in Figure 14.3g, the standard configuration as shipped from the factory. Note: In all configurations which apply voltage to the tip, an E-field cantilever holder is required.
Electric Force (EFM) Imaging Electric Field Gradient Detection—Preparation Voltage Applied to the Sample The jumper configuration in Figure 14.3i connects the Analog 2 signal from the NanoScope III controller (± 12 VDC range) to the sample. Enabling the Analog 2 Voltage Line The “Analog 2” voltage line is normally used by the NanoScope to control the attenuation (1x or 8x) of the main feedback signal. This application of EFM imaging uses the Analog 2 signal for EFM data.
Electric Force (EFM) Imaging Electric Field Gradient Detection—Preparation External Voltage Source Applied to the Tip In some cases, it may be advantageous to use voltages greater than 12 VDC, or to use a pulsed power supply. If an external source of voltage is to be applied to the tip, configure jumpers as shown in Figure 14.3j. Note: In all configurations which apply voltage to the tip, an E-field cantilever holder is required. Contact Veeco for more information. Figure 14.
Electric Force (EFM) Imaging Electric Field Gradient Detection—Preparation External Voltage Source Applied to the Sample In some cases, it may be advantageous to utilize voltages greater than 12 VDC, or to utilize a pulsed power supply. If an external source of voltage is to be applied to the sample, configure jumpers as shown in Figure 14.3k. Figure 14.3k Jumper configuration for applying external voltage to sample (for systems with the Basic Extender Module).
Electric Force (EFM) Imaging Electric Field Gradient Detection—Procedures 14.4 Electric Field Gradient Detection—Procedures Note: Amplitude detection is the only procedure described here that can be done without the Basic Extender Module; however, this method is no longer recommended (see “Without Basic Extender Module” on page 259). 1. Locate the two toggle switches on the backside of the Basic Extender box (Figure 14.4a), then verify that they are toggled as shown in Table 14.4a. Figure 14.
Electric Force (EFM) Imaging Electric Field Gradient Detection—Procedures 3. Mount a metal-coated NanoProbe cantilever into the electric field cantilever holder. MFMstyle cantilevers (225µm long, with resonant frequencies around 70kHz) usually work well. It is also possible to deposit custom coatings on model FESP silicon TappingMode cantilevers. Make sure that any deposited metal you use adheres strongly to the silicon cantilever. 4. Set up the AFM as usual for TappingMode operation.
Electric Force (EFM) Imaging Electric Field Gradient Detection—Procedures Figure 14.4c Shift in Phase at Fixed Drive Frequency 180 Phase (deg) ∆F0 90 ∆φ 0 Drive Frequency 258 • Under Interleave Controls set the Lift start height to 0nm, and Lift scan height to 100nm. (The lift height can later be optimized.) Set the remaining Interleave parameters (Setpoint, Drive amplitude, Drive frequency, and gains) to the main Feedback Controls values.
Electric Force (EFM) Imaging Electric Field Gradient Detection—Procedures • Adjust the sample or tip voltage to confirm that contrast is due to electrical force gradients. On very rough samples, contrast in LiftMode images may be from air damping between the tip and surface. It is often useful to look at the phase data in Scope Mode while adjusting the tip or sample voltage up and down. Contrast due to electrical force gradients should increase or decrease as the tip-sample voltage is changed.
Electric Force (EFM) Imaging Electric Field Gradient Detection—Procedures • Set the Drive frequency to the left side of the cantilever resonance curve, as shown in Figure 14.4e below. Figure 14.4e Amplitude Detection Cantilever Tune (Basic Extender Module not Installed). • For maximum sensitivity, set the Drive frequency to the steepest part of the resonance curve. As the tip oscillates above the sample, a gradient in the magnetic force will shift the resonance frequency F0; (see Figure 14.4d).
Electric Force (EFM) Imaging Surface Potential Detection—Theory 14.5 Surface Potential Detection—Theory Note: Surface potential detection EFM is only possible using the one of the extender modules or the NanoScope IV controller. This section does not apply to microscopes which are not equipped with the Basic or Quadrex Modules, or the NanoScope IV controller. The Basic Extender Module allows measurement of local sample surface potential.
Electric Force (EFM) Imaging Surface Potential Detection—Theory Figure 14.
Electric Force (EFM) Imaging Surface Potential Detection—Preparation 14.6 Surface Potential Detection—Preparation It is often desirable to apply a voltage to one or more areas of a sample. This may be done in two ways: by connecting a voltage to the sample mounting chuck, or by making direct contact to the sample. In both cases, jumper configurations in the bottom of the microscope must be changed to match the environment desired.
Electric Force (EFM) Imaging Surface Potential Detection—Preparation 14.6.1 Applying Voltage to the Sample Directly When voltage is applied directly to the sample, there is no need to reconfigure the jumpers. They should remain jumpered as shipped from the factory (Figure 14.6a), and the sample should be electrically insulated from the chuck. Connect the external voltage source directly to the sample by attaching fine gauge wire to appropriate contacts (e.g.
Electric Force (EFM) Imaging Surface Potential Imaging—Procedure A current-limiting resistor (e.g., 10–100MΩ) should be placed in series with the external voltage supply to protect the tip and sample from damage. Current-limited power supplies may also be used. Voltage leads should be connected to pins on the header using soldered, push-on connectors. Do not solder leads directly to the header pins. Heat may cause damage and/or make jumpering the pins difficult.
Electric Force (EFM) Imaging Surface Potential Imaging—Procedure Table 14.7a Basic Extender Module toggle switch settings for surface potential imaging.
Electric Force (EFM) Imaging Surface Potential Imaging—Procedure 7. Select the Interleave Controls command. This brings up a new set of scan parameters that are used for the interleaved scan where surface potential is measured. Different values from those on the main scan may be entered for any of the interleaved scan parameter. To fix any of the parameters so they are the same on the main and interleave scans, click on the green bullets to the left of particular parameter.
Electric Force (EFM) Imaging Surface Potential Imaging—Procedure 13. Optimize the lift heights. Set the Lift scan height at the smallest value possible that does not make the Potential feedback loop unstable or cause the tip to crash into the sample surface. When the tip crashes into the surface during the Potential measurement, dark or light streaks appear in the Potential image. In this case, increase the Lift scan height until these streaks are minimized. 14. Optimize the drive phase.
Electric Force (EFM) Imaging Surface Potential Imaging—Procedure 14.7.1 Troubleshooting the Surface Potential Feedback Loop The surface potential signal feedback loop can be unstable. This instability can cause the potential signal to oscillate or become stuck at either +10V or -10V. Here are some tips to see if the feedback loop is working properly with no oscillation: • Go into Scope Mode and look at the Potential signal. If oscillation noise is evident in the signal, reduce the FM gains.
Chapter 15 Calibration, Maintenance, Troubleshooting and Warranty This chapter provides detailed instructions for the fine calibration of Veeco MultiMode SPMs. Additionally, the latter part of the chapter focuses on problems commonly encountered during operation of the microscope and then concludes with maintenance procedures for the MultiMode SPM adjustment screws. Specifically, this chapter includes: • • • • Rev. B SPM Calibration Overview: Section 15.1 • Theory Behind Calibration: Section 15.1.
Calibration, Maintenance, Troubleshooting and Warranty • X-Y Calibration using Capture Calibration and Autocalibration: Section 15.5 • • Autocalibration: Section 15.6 • Fine-tuning for X-Y Calibration: Section 15.7 • • • Prepare System for Fine-Tuning: Section 15.7.1 • Measure Horizontally at 440V Scan Size: Section 15.7.2 • Measure Vertically at 440V Scan Size: Section 15.7.3 • Measure Horizontally at 150V Scan Size: Section 15.7.4 • Measure Vertically at 150V Scan Size: Section 15.7.
Calibration, Maintenance, Troubleshooting and Warranty • • • Rev. B Contact AFM Troubleshooting: Section 15.11 • False engagement: Section 15.11.1 • Head appears engaged but does not track surface features: Section 15.11.2 • Head does not engage: Section 15.11.3 • Head engages immediately: Section 15.11.4 • Displacement of material: Section 15.11.5 • Lines in the image: Section 15.11.6 • Problems with silicon nitride cantilevers: Section 15.11.
Calibration, Maintenance, Troubleshooting and Warranty • • Inspection: Section 15.14.1 • Remove Adjustment Screws: Section 15.14.2 • Inspect for Physical Damage: Section 15.14.3 • Clean Guide Bushings: Section 15.14.4 • Lubricate: Section 15.14.5 • Reinstall: Section 15.14.6 • Fuse Replacement Procedure: Section 15.15 • Vertical Engagement Scanners—Installation, Use, and Maintenance: Section 15.16 • • 274 Adjustment Screw Maintenance Procedure: Section 15.
Calibration, Maintenance, Troubleshooting and Warranty SPM Calibration Overview 15.1 SPM Calibration Overview Veeco employs a software-guided calibration procedure for all its microscopes. The procedural particulars of how calibration is executed using NanoScope software are beyond the scope of this document and include proprietary methods exclusive to Veeco.
Calibration, Maintenance, Troubleshooting and Warranty SPM Calibration Overview Veeco recommends that you adhere to the following scanner calibration schedule (see Table 15.1a). Table 15.
Calibration, Maintenance, Troubleshooting and Warranty SPM Calibration Overview Figure 15.1a Scanner Crystal Voltage and Photodiode Voltage Photodiode voltage Laser Photodiode array Cantilever 0 VDC -220 VDC +220 VDC Scanner Photodiode Voltage +3.0 0 Detector Sensitivity -3.0 -220 0 +220 Scanner Voltage The Microscope > Calibrate > Scanner function displays the Scanner Calibration dialog box, allowing users to enter the sensitivity of their scanner’s X-Y axes.
Calibration, Maintenance, Troubleshooting and Warranty SPM Calibration Overview Consider the sensitivity curve represented here: Voltage 440 V 150 V 0 0 Scanner Movement (nm) This curve typifies scanner sensitivity across the full range of movement. The vertical axis denotes voltage applied to the scanner. The horizontal axis denotes scanner movement. At higher voltages, the scanner’s sensitivity increases (i.e., more movement per voltage applied). At zero volts, the scanner is “motionless.
Calibration, Maintenance, Troubleshooting and Warranty SPM Calibration Overview Scanner Voltage Scanner Movement Time Through rigorous quality control of its scanner piezos, Veeco has achieved excellent modeling of scanner characteristics. Two calibration points are typically used for fine-tuning: 150 and 440V. (A third point is assumed at 0 nm/V.) These three points yield a second-order sensitivity curve to ensure accurate measurements throughout a broad range of scanner movements.
Calibration, Maintenance, Troubleshooting and Warranty SPM Calibration Overview 15.1.2 Calibration References As described above, each scanner exhibits its own unique sensitivities; therefore, it is necessary to precisely measure these sensitivities, then establish software parameters for controlling the scanner. This task is accomplished with the use of a calibration reference (see Figure 15.1c). Figure 15.
Calibration, Maintenance, Troubleshooting and Warranty Calibration Setup 15.2 Calibration Setup 15.2.1 Check Scanner Parameter Values If the system's original scanner parameters are deleted, copy the scanner parameters from the software CD shipped with every system. Individually purchased scanners are shipped with a head/ scanner disk containing backup files, or a hard copy of the scanner parameters. In the event that files are not found, fax or call Veeco for scanner calibration records. 15.2.
Calibration, Maintenance, Troubleshooting and Warranty Calibration Setup 15.2.3 Set Realtime Parameters Set parameters in the control panels to the following values: Panel Scan Controls Other Controls Channel 1 Parameter Setting Scan Size 440 V X offset 0.00nm Y offset 0.00nm Scan angle 0.00 deg Scan rate 2.44Hz Number of samples 256 Slow scan axis Enabled Z limit 440 V Units Volts Data type Height Z range ~ 20 Va a. Adjust the Z range parameter to obtain the best contrast. 15.
Calibration, Maintenance, Troubleshooting and Warranty Check Sample Orthogonality 15.3 Check Sample Orthogonality Check the sample scan for orthogonality along both the X- and Y-axes. If the scan is aligned along one axis of the scan but not another, it may be necessary to adjust the microscope’s Orthogonality parameter in the Scanner Calibration panel. 15.3.1 Measure Orthogonality 1. To measure a captured image’s orthogonality, view it using the Offline > View > Top View function. 2.
Calibration, Maintenance, Troubleshooting and Warranty Linearity Correction Procedure 3. Click OK to exit the Scanner Calibration panel 4. Capture another image and re-measure the angle. 5. Repeat correction of Orthogonality until the scanned image shows less than 0.5º of error. Note: 15.4 After a major change to the orthogonality parameter, you may need to physically realign the calibration standard to the image frame.
Calibration, Maintenance, Troubleshooting and Warranty Linearity Correction Procedure Adjust Fast Mag0 1. After engaging, click on Microscope > Calibrate > Scanner to open the Scanner Calibration window. As parameters values are changed, the effects will be seen on the display monitor. 2. Move the mouse cursor to the display monitor and select Zoom Out to produce a box whose size and position can be changed by alternate clicks on the left mouse button. 3.
Calibration, Maintenance, Troubleshooting and Warranty Linearity Correction Procedure Adjusting Fast Arg 1. Once the beginning third of the scan is equal to the end third, check to see if the center needs adjusting. 2. If the center features are too large for the box, decrease the Fast arg value. If the center features are too small, increase the Fast arg value. Change args by 0.2 to 0.5 units at a time. 3. Changes affect the entire scan, so continue to resize the zoom box after each change. 4.
Calibration, Maintenance, Troubleshooting and Warranty Linearity Correction Procedure 5. If the features of the end third are too large for the box, decrease the parameter. If the features are too small, increase the parameter. Note: Compare only parts of the current scan, not the previous scan. Figure 15.4c Slow Scan Linearization: Arg Slow Arg Too Small Slow Arg Too Large Adjusting Slow Arg 1. Follow the same instructions for Fast arg. 2.
Calibration, Maintenance, Troubleshooting and Warranty Linearity Correction Procedure 4. On the display monitor, select Dual Trace. If the two scope traces do not overlap, Fast mag1 needs adjusting. 5. On the Scan Controls panel, select Slow scan axis. When tall features appear on the scope trace, press the keyboard right or left arrow key to switch the Slow scan axis to Disabled. 6. Select Microscope > Calibrate > Scanner to open the Scanner Calibration box. 7. Select Fast mag1. 8.
Calibration, Maintenance, Troubleshooting and Warranty X-Y Calibration using Capture Calibration and Autocalibration 5. If the end of the scan is larger than the beginning, decrease the Slow mag1 value. If the end is too small, increase the value of Slow mag1. 6. Wait one complete frame with the new value before readjusting the Slow mag1 value. 7. Check the final result by capturing an image and checking it with the Offline > Modify > Zoom window.
Calibration, Maintenance, Troubleshooting and Warranty X-Y Calibration using Capture Calibration and Autocalibration 4. Click on CAPTURE to initiate the automatic calibration routine. Note: The microscope will begin an automatic series of scans on the reference which require about one hour to complete. During each scan, the scanner moves the piezo using carefully calculated movements. Many of these movements are unusual, giving rise to a variety of images which do not “look” like the normal reference.
Calibration, Maintenance, Troubleshooting and Warranty X-Y Calibration using Capture Calibration and Autocalibration Figure 15.5c Calibration Images 28.37 µm Partial Calibration Image Note: Improved Calibration Image After the first four images with the diagonal stripe pattern are captured, you can leave the system unattended while the program continues to completion. Some of the following images appear stretched in one dimension; however, this is normal. 9.
Calibration, Maintenance, Troubleshooting and Warranty Autocalibration 15.6 Autocalibration After the Capture Calibration routine is completed, the user measures surface features contained within each image and enters their dimensions into the software. The software compares its estimates with the actual (user-entered) dimensions to make final corrections. This portion of the calibration is carried out using the Offline > Utility > Autocalibration command.
Calibration, Maintenance, Troubleshooting and Warranty Autocalibration 3. Use the mouse to draw a line on the image. The line should be drawn to span as many features as possible, preferably connecting similar edges. For example, consider the following: Autocalibration Draw a vertical line 041 In this example, a line is drawn from the bottom edge of one feature to the bottom edge of another feature four rows away—a distance of 40µm.
Calibration, Maintenance, Troubleshooting and Warranty Fine-tuning for X-Y Calibration 15.7 Fine-tuning for X-Y Calibration Fine-tuning is usually performed at two Scan size settings: 150 and 440V. Both horizontal and vertical measurements of sample features are made, then compared with actual distances. Based upon this comparison, computer parameters are fine tuned. To fine tune your SPM for maximum XY measuring accuracy, review each of the steps below. Note: 15.7.
Calibration, Maintenance, Troubleshooting and Warranty Fine-tuning for X-Y Calibration Figure 15.7a Calibration Horizontal Reference Draw a horizontal line. Verify that the microscope’s measured distance agrees with the known horizontal distance. If there is significant disagreement between the two, fine tuning is required; go to Step 3 below. If the displayed distance agrees with the known distance, skip to Section 15.7.3. 3.
Calibration, Maintenance, Troubleshooting and Warranty Fine-tuning for X-Y Calibration 019 Figure 15.7b Scanner Calibration Dialog Box Multiply the quotient obtained in Step 3 by the X fast sens value shown on the Scanner Calibration panel. Enter the new value. This new value adjusts the scanner’s fast scan axis to more closely match calculated distances with actual feature distances. The new sensitivity setting takes effect as soon as it is entered.
Calibration, Maintenance, Troubleshooting and Warranty Fine-tuning for X-Y Calibration Divide the known distance by the distance displayed next to the line drawn in Step 2. Write this value down. 4. Select the Realtime > Microscope > Calibrate > Scanner function to display the Scanner Calibration dialog box. 5. Multiply the quotient obtained in Step 3 by the Y slow sens value shown on the Scanner Calibration panel, then enter the new value.
Calibration, Maintenance, Troubleshooting and Warranty Fine-tuning for X-Y Calibration Calculation Method 1. Select Realtime > Microscope > Calibrate > Scanner to display the Scanner Calibration dialog box. 2. Record the X fast derate or Y slow derate value. 3.
Calibration, Maintenance, Troubleshooting and Warranty Calibrating Z 15.8 Calibrating Z In terms of obtaining accurate Z-axis measurements, it is generally not difficult to obtain accurate X-Y calibration references. However, it is much more difficult to obtain accurate Z-axis results. Zaxis calibration is very sample-dependent. It is difficult to control Z piezo dynamics because the Zaxis does not move at a constant rate, as the X- and Y-axes do during scanning.
Calibration, Maintenance, Troubleshooting and Warranty Calibrating Z Figure 15.8a Z Calibration Image 5. Verify that the Z Center Position value shown next to the image display is close to 0 volts (±5 volts). 6. If the Z Center Position value is not close to zero, use the Realtime > Motor > Tip Up and Tip Down buttons to adjust. 15.8.2 Capture and Correct an Image 1. Capture an image by selecting Capture in the Realtime menu, or click on the CAPTURE icon.
Calibration, Maintenance, Troubleshooting and Warranty Calibrating Z Figure 15.8b Draw a Stopband 5. Click Execute to complete the flattening procedure. 6. Quit the dialog box. 15.8.3 Measure Vertical Features With the image corrected, its vertical features may now be measured. This is performed using Depth analysis to utilize more data points. 1. Select the Offline > Analyze > Depth command. Figure 15.8c Depth Analysis Screen Rev.
Calibration, Maintenance, Troubleshooting and Warranty Calibrating Z 2. Go to the display screen and draw a cursor box surrounding the entire image (see Figure 15.8d). Figure 15.8d Draw a Cursor Box 3. Click EXECUTE in the display monitor’s top menu bar. Note: Height data within the drawn cursor box displays on the monitor, showing two, prominent peaks. These peaks correspond to two elevations on the surface: the bottom of the pit and the top surface. There should be a line cursor on each peak. 4.
Calibration, Maintenance, Troubleshooting and Warranty Calibrating Z 7. Click QUIT to exit the Depth dialog box. Figure 15.8f Z Calibration Depth Dialog Box 15.8.4 Correct Z Sensitivity If the depth of the pit on the 10-micron silicon calibration reference deviates significantly from 200 nm, correct the Z sensitivity parameter in the Z Calibration dialog box. 1. Transfer to the Z Calibration dialog box by selecting Realtime > Microscope > Calibrate > Z. 2.
Calibration, Maintenance, Troubleshooting and Warranty Calibrating Z 15.8.6 Calculate Retracted and Extended Offset Deratings Piezoelectric materials exhibit greater sensitivity at higher voltages. In the steps outlined above, the Z-axis calibrates while scanning near the middle of its voltage range (i.e., Z Center Position ~ 0 V). In this section, you will calibrate the Z-axis piezo while extended and retracted to offset the increased sensitivity. 1.
Calibration, Maintenance, Troubleshooting and Warranty Calibrating Z 15.8.7 Finding a Pit with an “A” Scanner Since it may be difficult and/or time consuming to locate a pit in the sample using an “A” scanner, an alternate method of locating a pit is to use the Scope mode in Realtime imaging. 1. After engaging on the surface of the sample set both Realtime Planefit and Offline Planefit to offset. Got to Scope mode. 2.
Calibration, Maintenance, Troubleshooting and Warranty Calibration of “A” Scanners for Atomic-scale Measurement 15.9 Calibration of “A” Scanners for Atomic-scale Measurement The “A” scanner is the smallest scanner, with a total travel of approximately 0.4µm along each axis. Its compact design lends excellent stability for atomic scans, and requires slightly modified X-Y calibration procedures. These are treated in this section.
Calibration, Maintenance, Troubleshooting and Warranty Calibration of “A” Scanners for Atomic-scale Measurement 3. Engage the surface and adjust the Integral gain and Setpoint to obtain a good image. Keep the Setpoint low if possible, and the Z Center Position close to 0V. Notice that the Scan rate is set much higher (~ 61 Hz) for atomic-scale images, this to defeat some of the noise due to thermal drift.
Calibration, Maintenance, Troubleshooting and Warranty Calibration of “A” Scanners for Atomic-scale Measurement 5. Go to the Offline > View > Top View option and measure the spacings between atoms using the mouse. Depending upon whether the sample is graphite or mica, measure the spacings as shown below. A C A = 0.519nm B = 0.900nm C = 1.37nm B Atomic Spacing for Mica A C A = 0.255nm B = 0.433nm C = 0.
Calibration, Maintenance, Troubleshooting and Warranty Quick Guide to Piezo Tube Calibration Do not adjust the derating parameters for atomic-scale imaging, including: • X fast derate • X slow derate • Y fast derate • Y slow derate • Retracted offset der • Extended offset der As referenced in Section 15.7.6, you must calibrate the sensitivity parameters with the Scan angle set at both 0 degrees and at 90 degrees. 7. Complete the Z-axis calibration using a silicon calibration reference.
Calibration, Maintenance, Troubleshooting and Warranty Quick Guide to Piezo Tube Calibration 7. Reduce the scan size to 150V and adjust the Fast and Slow mag1 values to make the image linear. Typical values are 0.6 - 1.5. 15.10.2 Run Autocalibration Software (Factory Operation) Note: You can use Fine Tune in place of Autocalibration. 1. Select Calibrate > Capture Calibration. Allow the software to run through the entire sequence of capturing 12 images.
Calibration, Maintenance, Troubleshooting and Warranty Quick Guide to Piezo Tube Calibration 6. Adjust the X Slow sens until the slow axis is correct. 15.10.4 Calibrate the Z Piezo This calibration is necessary during routine maintenance. 1. Set the Scan size to 150V. Scan rate to 2.44Hz. 2. Adjust the Z center voltage to 0V +/- 5V. Use Realtime > Motor > Tip Up or Tip Down if necessary. 3. Capture an image. 4. Use Flatten 1st order to flatten the image. 5.
Calibration, Maintenance, Troubleshooting and Warranty Quick Guide to Piezo Tube Calibration Figure 15.10a Calibration Recommended Parameters To the side of some scan parameters are the recommended scan size and scan angle setting for obtaining accurate calibration values.
Calibration, Maintenance, Troubleshooting and Warranty Contact AFM Troubleshooting 15.11 Contact AFM Troubleshooting Depending on the operating mode being used, the symptoms and subsequent resolution may vary. For this reason, problems listed in this chapter are divided into Contact AFM (see Section 15.11) and TappingMode (see Section 15.12). STM problems are described in Chapter 9 of this manual. Some of the problems and cures associated with contact AFM are also relevant to TappingMode.
Calibration, Maintenance, Troubleshooting and Warranty Contact AFM Troubleshooting 15.11.2 • Check the cabling between the computer and the controller, and between the controller and the microscope. Any discontinuity in the microscope signals can cause an immediate engage. • The Setpoint may be set more negative than the vertical deflection (A-B) voltage (this applies only to contact AFM modes).
Calibration, Maintenance, Troubleshooting and Warranty Contact AFM Troubleshooting 15.11.4 Head engages immediately If the microscope engages immediately after the Engage icon is selected, the problem may be one the following: 1) The Setpoint may be lower than the feedback voltage. Select Withdraw a few times and verify that the vertical deflection reads a negative voltage of -1.0 to -4.0V. Adjust the Setpoint to zero or slightly above and try to engage again.
Calibration, Maintenance, Troubleshooting and Warranty Contact AFM Troubleshooting (both of which are on the same side of the chip) will have difficulties with the laser optics due to laser beam spillage over the side of the cantilever. This effect is more pronounced for samples which are highly reflective. Using a microscope that has an interferometric objective lens, it is possible to observe five or more contour lines following the length of the legs of the cantilever on a warped cantilever probe.
Calibration, Maintenance, Troubleshooting and Warranty Contact AFM Troubleshooting vertical drift is indicative of optical path drift, while a horizontal drift is due to a mechanical change in tip-to-sample separation. Use the following as first steps in correcting drift: • Verify that the sample, tip and stage are all stabilized.
Calibration, Maintenance, Troubleshooting and Warranty Contact AFM Troubleshooting Selecting a large Scan size and a high scan rate for a few scans can “sweep” an area clear. Decreasing the Scan size to image within the “swept” area can improve the quality of atomic images. Finally, adjust the force exerted on the sample. Engagement requires a positive deflection of the cantilever, but the microscope will operate at much lower forces and lowering the force sometimes improves the image quality.
Calibration, Maintenance, Troubleshooting and Warranty TappingMode AFM Troubleshooting 15.12 TappingMode AFM Troubleshooting Depending on the operating mode being used, the symptoms and subsequent resolution may vary. For this reason, problems listed in this section are divided into Contact Mode (see Section 15.11) and TappingMode (see Section 15.12). STM problems are described in Chapter 9 of this manual. Some of the problems and cures associated with contact AFM are also relevant to TappingMode.
Calibration, Maintenance, Troubleshooting and Warranty TappingMode AFM Troubleshooting With Streaks 15.12.2 022 021 Figure 15.12a Images With/Without Streaks Without Streaks Lines across the image Lines oriented in the fast scan direction can be caused by the tip sticking to the surface. This condition may be remedied by increasing the RMS voltage. Working with a larger RMS has the effect of giving the tip more energy to pull off of the surface.
Calibration, Maintenance, Troubleshooting and Warranty TappingMode AFM Troubleshooting 15.12.3 Rings around features on the surface This effect might also be described as the image looking as though it is half submerged beneath water (see Figure 15.12b). This is caused by operating with a drive frequency too close to cantilever resonance. Use the arrow keys to increment the drive frequency a little lower. Do this while watching the Realtime scan. Be aware that the RMS voltage might also reduce.
Calibration, Maintenance, Troubleshooting and Warranty TappingMode AFM Troubleshooting 15.12.4 Multiple or repeating patterns The tip is probably chipped (see Figure 15.12c and Figure 15.12d). This is usually caused by using too much tapping force on the surface, or because the tip encountered a feature too high to successfully traverse. If this occurs, change the tip. Note: Operating with a smaller difference between the RMS voltage and the Setpoint voltage means that less tapping force is being used.
Calibration, Maintenance, Troubleshooting and Warranty Fluid Imaging Troubleshooting 15.12.5 Image goes white or black If the image goes white or black after a few scans and the Z Center Position voltage is still within range, check the Offline Planefit sub-command on the control monitor. Offline Planefit is normally set to Full. (See full description of the Offline Planefit command in Digital Instrument’s Command Reference Manual. 15.13 Fluid Imaging Troubleshooting 15.13.
Calibration, Maintenance, Troubleshooting and Warranty Adjustment Screw Maintenance Procedure • Replace the O-ring with a slice of thin-walled glass, plastic, or stainless steel tubing. The diameter and thickness of the ring of tubing should be chosen to prevent contacting the inner or outer walls of the circular groove in the glass cantilever holder. This gives the head more room to move laterally during engagement and for positioning the tip over the sample surface.
Calibration, Maintenance, Troubleshooting and Warranty Adjustment Screw Maintenance Procedure Ball Bearing (top) (Scanner body) Setscrew (applies pressure to bushing) Plastic bushing Brass threaded insert Screw Screw hole (on 3-screw models) Knob Adjustment screws are threaded into brass inserts, which are affixed to the scanner body with epoxy. Although screws are not heavily lubricated, a light film of oil is applied to them at the factory to prevent galling.
Calibration, Maintenance, Troubleshooting and Warranty Adjustment Screw Maintenance Procedure 15.14.2 Remove Adjustment Screws To remove adjustment screws, do the following: 1. Remove SPM head and disconnect the scanner body from the Small Sample base by pulling its cable connector straight up. Hold the scanner body firmly in your hand. 2. Gently turn each screw to check for resistance. Turn counterclockwise until backed out of its screw hole.
Calibration, Maintenance, Troubleshooting and Warranty Adjustment Screw Maintenance Procedure 2. Use a swab stick (e.g., Q-tip, Puritan swab, etc.) to carefully clean grit from the threaded brass inserts. Be sure to remove all grit from threads; air dry. 3. Carefully inspect surfaces for signs of wear or damage. If small burrs are visible inside of the threaded brass inserts, they may removed by gently sanding with fine emory cloth, then recleaned using a swab and solvent.
Calibration, Maintenance, Troubleshooting and Warranty Fuse Replacement Procedure 15.15 Fuse Replacement Procedure The NanoScope III ships with 6 fuses: 3 identical fuses in use and 3 spare fuses. The fuse characteristics are silk-screened on the back of the NanoScope controller (see Table 15.15a). Table 15.15a NanoScope Controller Fuse Characteristics Fuse Selection Line Voltage F1 F2 F3 100V 2.0A 800mA 800mA 120V 2.0A 800mA 800mA 220V 1.0A 400mA 400mA 240V 1.
Calibration, Maintenance, Troubleshooting and Warranty Vertical Engagement Scanners—Installation, Use, and Maintenance 15.16 Vertical Engagement Scanners—Installation, Use, and Maintenance Figure 15.16a MultiMode Scanner Veeco now offers “E” and “J” scanners which permit vertical engagement without significant lateral movement. The vertical scanners feature the following: • Completely motorized tip-sample engage. • Fully vertical engage head does not tilt. • Easy to locate tip on desired scan area.
Calibration, Maintenance, Troubleshooting and Warranty Vertical Engagement Scanners—Installation, Use, and Maintenance 15.16.1 Hardware Installation Installation of the vertical scanner is very similar to earlier models. To install the vertical scanner, do the following: 1. Remove old scanner: If the SPM is engaged, disengage from the sample by clicking on the Withdraw icon several times. Unplug and remove the SPM head from the microscope. Remove the sample, then unplug and remove the old scanner body.
Calibration, Maintenance, Troubleshooting and Warranty Vertical Engagement Scanners—Installation, Use, and Maintenance The scanner file may be copied with any name, as long as it includes a .SCN extension. Make certain the vertical scanner’s file name is not the same as a preexisting file; otherwise, it will overwrite the preexisting file. 4. Once the scanner file is copied, reboot the NanoScope software to resume.
Calibration, Maintenance, Troubleshooting and Warranty Troubleshooting the Vertical Engagement Scanners 15.17 Troubleshooting the Vertical Engagement Scanners 15.17.1 Scanner is not properly calibrated Verify that the scanner’s parameter file has been properly copied to each of the computer’s \EQUIP directories. Check the parameter file name; it should include a .SCN extension (e.g., XXXXJV.SCN). Try to reselect the scanner using the Realtime > Microscope > Scanner panel.
Calibration, Maintenance, Troubleshooting and Warranty Warranty 15.18 Warranty All new catalog-listed standard equipment sold and/or manufactured under Veeco labels is warranted by Veeco to be free of defects in material and workmanship if properly operated and maintained. This one-year warranty covers the cost of necessary parts and labor (including, where applicable as determined by Veeco, field service labor and field service engineer transportation) during the warranty period.
Calibration, Maintenance, Troubleshooting and Warranty Warranty Warranty Eligibility To be eligible for the above warranties, purchaser must perform preventative maintenance in accordance with the schedule set forth in the manual provided. Veeco assumes no liability under the above warranties for equipment or system failures resulting from improper operation, improper preventative maintenance, abuse or modifications of the equipment or system from the original configuration.
Index Symbols . 218, 231 A Adjustment Screws maintenance 324 Aliasing 211 Amplitude 118 Atomic Force Microscope (AFM) operator precautions 10 sample precautions 12 Average count 185 B Bias Voltage 147 Bimorph Resonant Frequency 207 C Calibration standard 280 Z 299— 305 Calibration Procedures 306— 309 cantilever substrates 57 Cantilever Tune 115 Cantilever Tune initial settings 111 cantilevers 57 Cantilevers.
Index adjustment 191— 192, 192— 197 Force Modulation 204— 212 edge effects 210 operating procedure 206— 211 principles of 206 Frequency Modulation with MFM 232 Frequency Sweep 110 with MFM 230, 258 Frictional Measurements See Lateral Force Microscopy 167— 173 G Graph range 186, 192 H Hardware components listed 49— 50 Hardware Description 3 Hazards symbols 5 Head adjustment 107 laser aiming 88 preparation 69— 77 Head 50 Height 99, 118, 119 Highpass 228, 257 Highpass Filter 101 M I Icons attention 5 elec
Index sample safeguards 12 voltage 7 wiring 7, 8 Other Controls 94 P Parameters show 91, 105, 152 Personal Injury symbol 5 Probe menu Run Continuous 190 Run Single 190 Stop 190 Probe Tips EFM 227 engagement 95 force modulation 212 geometry 59— 63, 221 LFM 170 MFM 227 removal from substrates 57, 64 selection 98— 99 silicon 57— 63 silicon nitride 315 STM 149, 151 tuning 109— 113 Property Damage symbol 5 Proportional gain 211 Proportional gain 38— 42, 100, 113, 118, 232 R Radiation operator safety 9 Retrace
Index Z scan start 184, 203 Zoom In 208 Zoom In 112 laser hazard 5 lifting hazard 5 mechanical crushing hazard 5 safety 5 T TappingMode 103— 203 44 principles of 43— set-up 85 Tip Down 191, 193 Tip Holder installation fixture 77 Tip Up 191 to 230 Trace 116 Troubleshooting 319— 324 adjustment screws 324 calibration 306— 309 contact force too high 315 control loop explained 37 drift during fluid imaging 323 loss of Z center position 316 no engagement 313— 314 poor image lines 315, 320 poor image repeating
