| Abstract: | The scanning speed and quality of images obtained with a scanning tunnelling microscope can be increased by replacing the tunnelling tip holder with an active, high resonance frequency piezoelectric positioner. The combination tip holder and positioner has a resonance frequency near 100 kHz, allowing fast closed-loop feedback control of the STM. With appropriate electronic shielding, the active tip holder can also be used to modulate the tip to surface distance at high frequencies for work function mapping. The high speed positioner is complemented by a ‘tip-saver’ circuit which senses imminent tip-surface contact, preventing tip crashes. The circuit, when driving the fast positioner, has a response time of under 20 μs and is not subject to the oscillation problems normally associated with closed-loop feedback systems operated at high gains and large signal bandwidths. |
