Optics and Precision Engineering, Volume. 18, Issue 4, 906(2010)
Self-oscillating electronics for improving scanning speed in AF/PSTM
An atomic Force Photon Scanning Tunneling Microscope (AF/PSTM) is reported here,which uses a shift in resonance frequency to control the distance between a sample and a fiber probe.For self-oscillating tapping mode AF/PSTM applications, a sharp end and large conical angle optical fiber tip with an apex diameter smaller than 100 nm and a cone angle of 60~90° is fabricated.The tip is mounted on a piezo,then the piezo is placed in a positive feedback circuit to excite the probe to oscillate.The oscillation frequency of the tip is demodulated by a PLL, and its value is maintained a constant by controlling the negative feedback loop of the Z piezo to track the sample surface.Both theory and experiment are carried out to compare the externally excitation mode and self-oscillating mode.Results show that the self-oscillation mode reduces the response time of the tip in theory,and the bandwidth of self-oscillating mode in proposed AF/PSTM is 50 Hz in experiments, which is higher an order of magnitude than that of externally excitation mode response.A sample of grating is scanned by proposed instrument with a scanning rate of 1 Hz,and results demonstrate that the topography and optical images obtained by self-excitation mode have clearer contrast than those obtained by externally excitation mode.Besides faster response, the self-oscillating mode can improve the system resolution by increasing Q without effecting on the system response speed.
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WANG Zhao, WU Shi-fa, LIU Kun. Self-oscillating electronics for improving scanning speed in AF/PSTM[J]. Optics and Precision Engineering, 2010, 18(4): 906
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Received: Oct. 15, 2009
Accepted: --
Published Online: Aug. 31, 2010
The Author Email: Zhao WANG (wangzhao_1978@yahoo.com.cn)
CSTR:32186.14.