Topological Magnetism Group

Abstract:

We report about a new technique for the investigation of SAW fields within SAW devices reaching submicron lateral resolution. The scanning acoustic force microscope (SAFM) is based on a standard force microscope and utilizes the nonlinear force curve in the sense of a mechanical diode. Varying wave amplitudes therefore lead to different shifts of the cantilever's rest position. With SAFM we investigated SAW devices with center frequencies above 600 MHz. We found a local effect of massloading on the standing wave amplitude within IDTs. Furthermore, we measured the dynamic behavior of the IDT's wave pattern when sweeping the frequency.

Abstract:

A high frequency oscillating Au (111) surface was measured with atomic resolution using a modified scanning tunneling microscope. On the atomic scale propagating surface acoustic waves lead to oscillations of atoms on elliptical trajectories, with the axes being determined by the material parameters of the surface. Since those oscillation frequencies are much higher than the scan frequencies the topography contrast is reduced. This basic problem is solved by measuring a stroboscopic snapshot seeing a defined state of oscillation. The atomic resolution of the phase and the amplitude contrast is explained by the superposition of the surface topography and the oscillation trajectory. © 1996 American Institute of Physics.

Abstract:

Starting from the conventional microprobe techniques, a scanning acoustic tunneling microscope (SATM) and a scanning acoustic force microscope (SAFM) have been developed to detect particle displacements at solid surfaces up to GHz frequencies. Based on the non-linear dependence of the tunneling current in SATM and of the forces in SAFM on the tip to surface distance, respectively, it is demonstrated that wave field parameters of surface acoustic waves can be measured with a lateral resolution in the submicrometer range.