METHOD TO CHARACTERIZE THE VIBRATIONAL RESPONSE OF A BEETLE TYPE SCANNING TUNNELING MICROSCOPE

We describe a method for analyzing the external vibrations and intrins ic mechanical resonances affecting scanning probe microscopes by using the microscope as an accelerometer. We show that clear correlations c an be established between the frequencies of mechanical vibrational mo des and the frequencies of peaks in the tunnel current noise power spe ctrum. When this method is applied to our ''beetle'' type scanning tun neling microscope (STM), we find unexpected low frequency ''rattling r esonances'' in the 500-1700 Hz range that depend on the exact lateral position of the STM, in addition to the expected mechanical resonances of the STM above 4 kHz which are in good agreement with theoretical e stimates, We believe that these rattling resonances may be a general p roblem for scanning probe microscopes that use some type of kinetic mo tion for coarse positioning. (C) 1997 American Institute of Physics.