Professor Thorsten Hesjedal FInstP

Abstract:

We present measurements of the reflection and mode conversion of surface acoustic waves (SAWs) by scanning acoustic force microscopy (SAFM). The SAFM offers a unique combination of high lateral resolution and high sensitivity towards acoustic modes of all polarizations. Since a SAW mixing experiment of two waves can be performed even if the amplitude difference between both waves is 40 dB, wavefields of extremely small amplitudes can be investigated. Using SAFM, the reflection of SAWs from a metallic wedge is investigated with submicron lateral resolution. We are able to identify two reflected wave modes, a Love and a non-coupling Rayleigh mode, by measuring their phase velocities.

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.