Professor Thorsten Hesjedal FInstP

Abstract:

Scanning Acoustic Force Microscopy (SAFM) has been used to study elementary surface acoustic wave phenomena with nanoscale spatial resolution. The SAFM technique is capable of detecting acoustic wave properties of arbitrarily polarized modes with sub-wavelength resolution and unmatched sensitivity. Elementary model systems like symmetric single finger wave sources and circular wave sources are studied for the first time in detail.

Abstract:

We used multimode Scanning Acoustic Force Microscopy (SAFM) for the simultaneous phase velocity measurement of differently polarized SAWs with non-collinear propagation directions at a submicron lateral scale. By analyzing the torsion of the cantilever in addition to its bending (standard SAFM), normal and in-plane oscillation components due to acoustic waves can be measured. Investigating the mixing of complementary oscillation components of crossed Rayleigh and Love waves on the layered system SiO2ST-cut quartz, both phase velocities were obtained simultaneously at the same sample spot.

Abstract:

We present the study of the influence of surface acoustic waves (SAWs) on point-contact friction in scanning force microscopy. First, the effect of friction reduction due to Rayleigh-type SAWs was demonstrated. In order to visualize the dependence of this effect on the wave amplitude, we mapped standing wave fields in two dimensions. In order to detect and to distinguish between the influence of in-plane and vertical surface oscillation components on the cantilever's torsion and bending, we employed both lateral force microscopy (LFM) and multimode scanning acoustic force microscopy (SAFM). We found that the friction reduction effect is only due to the vertical oscillation component. Moreover, as this effect doesn't appear for purely in-plane polarized Love waves, we conclude that the mechanical diode effect is most probably responsible for the SAW-induced lubrication.

Abstract:

The first experimental investigation of a single gap surface acoustic wave (SAW) source on GaAs is reported. Using scanning acoustic force microscopy, SAWs are measured with sub-wavelength resolution and an unmatched sensitivity. Phase and amplitude images reveal the radiation characteristics of a single gap source, allowing for a deeper insight into SAW device operation and future design improvements.

Abstract:

We present scanning acoustic force microscopy (SAFM) mixing experiments of differently polarized surface acoustic waves (SAW) with noncollinear propagation directions. The phase velocities of the SAWs are measured at a submicron lateral scale, employing a multimode SAFM that is capable of detecting the wave's normal and in-plane oscillation components. Hereby, the down conversion of the surface oscillations into cantilever vibrations due to the nonlinearity of the tip-sample interaction is utilized. The simultaneous determination of the phase velocities within a microscopic sample area is demonstrated for the mixing of Rayleigh and Love waves on the layered system SiO2/ST-cut quartz. © 2000 American Institute of Physics.