Surface acoustic wave investigation by ultrahigh vacuum scanning tunnelingmicroscopy

The scanning acoustic tunneling microscope is based on the conventional sca nning tunneling microscope and extends its topography-mapping capability to the investigation of both amplitude and phase of surface acoustic waves (S AWs) with frequencies in the MHz range. The mechanical oscillation of the s urface induced by the SAW modulates the tunneling current. By adding a sinu soidal high frequency signal to the dc tip voltage this ac tunneling curren t signal is mixed down to an easily detectable low frequency signal. Here, we report the first ultrahigh vacuum (UHV)-compatible version of this techn ique including provision for sample transfer and in situ surface preparatio n. Since both signal-to-noise ratio and spatial resolution are significantl y enhanced in UHV, acoustic oscillations of topography features can be inve stigated on the nanoscale. At present, SAW frequencies up to 400 MHz have b een successfully fed into the UHV system. (C) 2001 American Vacuum Society.