Professor Thorsten Hesjedal FInstP

Abstract:

We present the submicron visualization of surface acoustic wave (SAW) fields within interdigital transducers (IDTs) obtained by a scanning acoustic force microscope. Utilizing the nonlinear force curve of the tip-to-surface interaction, a periodic deflection of the cantilever appears when the SAWs are excited intermittently. This deflection depends on the amplitude of the surface oscillation and was measured by lock-in technique. SAWs with operating frequencies above 600 MHz were detected. The influence of the mass loading on the local oscillation amplitude was studied for various layer thicknesses of the IDT electrodes. © 1997 American Institute of Physics.

Abstract:

We measured the phase velocity of surface acoustic waves (SAWșs) with a scanning acoustic force microscope (SAFM) and achieved a maximum lateral resolution of 19.9 nm. The phase measurement of high-frequency waves with a slowly responding SAFM cantilever was perfomed by frequency mixing at its nonlinear force curve. For Au layers of different thicknesses the SAW dispersion was studied on a lateral scale of 200 nm and compared to calculated data. © 1997 The American Physical Society.

Abstract:

We report on the investigation of surface acoustic wave (SAW) fields by scanning acoustic force microscopy (SAFM), reaching submicron lateral resolution. The SAFM is based on a standard atomic force microscope and utilizes the non-linear force curve in the sense of a mechanical diode. The surface oscillation therefore leads to a shift of the cantilever's rest position. With SAFM we investigated SAW transducers operating at frequencies above 600 MHz. We measured the dynamic behaviour of the wave pattern within the transducers when sweeping the frequency and found a local influence of mass loading on the standing SAW amplitude. Furthermore, the first images of SAW diffraction and scattering are shown. © 1997 by John Wiley & Sons, Ltd.

Abstract:

A method is presented for the universal probing of surface acoustic waves (SAWs). For measuring high frequency SAWs by scanning tunneling microscopy (STM) a stroboscopic snapshot technique was employed, named scanning acoustic tunneling microscopy. The amplitude and the phase of a state of oscillation within a SAW field are a superposition of the surface topography and the oscillation trajectory. Measuring with atomic resolution the observed contrast can be understood by a spherical tunneling model. A STM based system is proposed that reaches submicron resolution for the quantitative evaluation of elastic constants. With this system the velocity dispersion is obtained from the detection of laser generated SAW pulses by a broadband STM. Scanning acoustic tunneling spectroscopy using different acoustic modes opens a door for quantitative studies of nanoscale structures. © 1997 American Vacuum Society.

Abstract:

This paper reports about the first determination of the phase velocity of surface acoustic waves (SAWs) on the nanometer scale. With a scanning acoustic force microscope (SAFM) a maximum lateral resolution of 19.9 nm has been achieved. This is almost two orders of magnitude better than the resolution of standard quantitative acoustic microscopy. The key of measuring the phase of high frequency signals with a slowly responding SAFM cantilever is frequency mixing at its non-linear force curve. For demonstrating its abilities SAW dispersion was studied on Au layers of different thicknesses by SAFM over a lateral distance of down to 200 nm.