UBC Theses and Dissertations
Optical end point sensing and digital control of a scanning tunneling microscope Chahal, Anthony M.
The problem addressed in this thesis is that of digitally controlling a Scanning Tunneling Microscope and implementing end point sensing to close the control loop for accurate X-Y positioning of the microscope tip. This first part entails modifying a microscope with an analog controller so that it may be interfaced to a DSP system running on a personal computer. The second part is designing and incorporating an optical end point sensor into the head of the microscope to improve absolute position control of the tip in the scanning plane by overcoming hysteresis and creep in the piezoelectric scanning tube actuator. The sensor would also improve the repeatability of imaging and facilitate random access positioning of the tip to allow for more sophisticated scanning trajectories. The digital controller was successfully implemented. Images of sputtered gold obtained with the new controller were of comparable quality to those obtained using a microscope under analog control. A single axis version of the sensor was developed which was used independently of the microscope to measure the hysteresis and creep that were present in the piezoelectric actuator. The sensor had a resolution of 8.5 nm, but was not completely integrated into the digital control and imaging system.
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