Thin film quantum materials

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.

Abstract:

Grating-like metal electrodes supplied with high- and low-frequency voltages were investigated by a Scanning Acoustic Force Microscope (SAFM). On piezoelectric LiNbO3, these electrodes form an interdigital transducer which generates surface acoustic waves according to the charge distribution on its electrodes when excited at a transducer's passband frequency. The influence of surface deformation and of surface charges on the cantilever deflection of the SAFM in contact and non-contact mode was systematically studied. Comparing the images of the electrodes which were prepared on piezoelectric and dielectric substrates, surface deformation and charge distributions were qualitatively separated. © 1995 Springer-Verlag.