AVS 51st International Symposium
    Surface Science Monday Sessions
       Session SS-MoP

Paper SS-MoP27
Design of a High-Speed Digital Feedback Loop for Scanning Tunneling Microscope Applications

Monday, November 15, 2004, 5:00 pm, Room Exhibit Hall B

Session: Poster Session
Presenter: E. Ulin-Avila, University of California, Riverside
Authors: E. Ulin-Avila, University of California, Riverside
A. Liu, University of California, Riverside
B.V. Rao, University of California, Riverside
L. Bartels, University of California, Riverside
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We present the development of a digital feedback loop for Scanning Tunneling Microscope (STM) operation that is capable of updating the tip height and xy position at a frequency of 170kHz. This feedback frequency approximates the maximum update rate of standard 16bit AD/DA converters of 200kHz. Its digital nature allows for precise linearization of the exponential dependence of the tunneling current on the tip-sample separation thereby avoiding oscillatory behavior common with non-linearized feedback loops. In addition, the digital setup allows full control of the z-motion of the tip at any point in time, which permits versatile tip control during lateral manipulation and rapid spectroscopy. The feedback loop incorporates a commercial digital signal processor board (Innovative Integration) utilizing a TI C6200 processor. First application of the new system will be presented.