J. Schmidt et al., Microwave-frequency alternating current scanning tunneling microscopy by difference frequency detection: Atomic resolution imaging on graphite, REV SCI INS, 70(8), 1999, pp. 3377-3380
We present a detailed description of an experimental setup for alternating
current scanning tunneling microscopy, in which two slightly detuned high f
requency signals are mixed at the tunneling junction and the resulting diff
erence frequency signal is amplified using conventional scanning tunneling
microscope electronics. This signal is used to control the distance between
the microscope tip and the sample. With graphite as a model surface atomic
resolution images have been obtained. It is demonstrated that the origin o
f the generated signal on graphite is the nonlinearity of the static curren
t-voltage characteristics. (C) 1999 American Institute of Physics. [S0034-6
748(99)03608-4].