Instruction manual

Electric Force (EFM) Imaging
Electric Field Gradient Detection—Procedures
260 MultiMode SPM Instruction Manual Rev. B
• 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 F
0
; (see Figure 14.4d). Tracking the variations in oscillation
amplitude while in LiftMode yields an image of the electric force gradients. Either side
of the resonance may be used, though we have obtained slightly better results on the low
side, as shown in Figure 14.4d
• When using Amplitude Detection, optical interference may sometimes appear in the
lift (magnetic force) image when imaging highly reflective samples. Optical
interference appears as evenly spaced, sometimes wavy lines with about 1–2µm spacing
superimposed on the lift image. This occurs when ambient laser light (i.e., light passing
around or through the cantilever, then reflecting off the sample) interferes with laser
light reflecting from the cantilever. Interference can be alleviated by moving the beam
spot up the cantilever away from the tip; about one-third of the cantilever length from
the tip usually works well. On the MultiMode head, the adjustment can be refined by
carefully moving the beam spot laterally on the cantilever while scanning until
interference fringes are minimized.
Note: Optical interference is essentially eliminated by using phase detection or
frequency modulation, available only with the Basic Extender Module.