COARSE APPROACH: This STM employs a compact design where the Z-coarse (a slip-stick motor, 6 piezo stacks driven at the same time with the same waveform) and Z-fine motion of the tip is done by the same set of (shear) piezos. The same HV amplifier is used for Z-coarse and Z-fine. This means that the available voltage range has/can to be reserved for the Z-coarse and Z-fine motion, as depicted in the figure here under:

This has the limitation that the Z-range for current probing would be too small. Furthermore, this can only be realized using the “Analog Tip Ramp” method with the RHK electronics, and with this method the 2nd DAC will have to be used as well and piped into Z-modulation input nr.2 which mixes in the DAC input with the Z-scan signal with NO amplification. To have an amplification different from 1, the RHK box would have to be hacked and a gain resistor changed. Possible but possibly unwanted. DAC 2 should also remain free for spectroscopy as well.

A solution is to use the whole range for tip fine motion during approach and use the time-reversal method to the waveform to walk back, instead of inverting the polarity, as sketched here under:

HOWTO: In Approach Control, Main: use always “Tip Retract” method, with TTL-Feedback control, Tip back in motion ON.

1. APPROACH: Waveform: Parabola, Asymmetry: 0%
2. RETRACT: Waveform: Sawtooth, Asymmetry: 100%

Typical cycle time is 200-250 μs.