Probing of surface acoustic wave fields by scanning tunneling microscopy

With STM the tunneling tip can be used as a local probe to detect the amplitude and phase of the acoustic wave field at the surface of a solid. The decisive point of this method is the application of an additional RF signal to the DC tip voltage. Due to the nonlinear dependence of the tunneling current on the tip to surface distance there is a mixing of the two RF frequencies. This leads to a low frequency component of the tunneling current which can be analyzed with conventional STM electronics. The authors report on calculations of the phase behaviour of surface acoustic waves on rough surfaces and compare the results with phase measurements