Instruction manual

SPM Fundamentals for the MultiMode
Hardware
20 MultiMode SPM Instruction Manual Rev. B
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. Newer, “vertical” scanners use
motorized single-screw adjustment.
Figure 2.1c MultiMode SPM Head and Major Components
Photodiode array—The four elements of the quad photodiode (position sensitive detector) are
combined to provide different information depending on the operating mode. In all modes the four
elements combine to form the SUM signal. The amplified differential signal between the top two
elements and the two bottom elements provides a measure of the deflection of the cantilever. This
differential signal is used directly in the contact AFM. It is fed into an RMS converter (or phase
module if attached) for TappingMode operation. Similarly, the amplified differential signal between
the sum of two left photodiodes and the sum of the two right photodiodes provides a measure of the
torsion in the cantilever and is used in Lateral Force Microscopy (Image data type: Friction).
Figure 2.1d shows the arrangement of the photodiode elements in the MultiMode head. Different
segments of the photodetector are used for generating AFM and LFM signals.
Head Y-axis stage adjustHead X-axis stage adjust
Photodiode adjust
Laser Y-axis adjust
Laser X-axis adjust
KEY
1. Laser
2. Mirror
3. Cantilever
4. Tilt Mirror
5. Photodetector