Thin film quantum materials

Abstract:

We present measurements of surface acoustic wave (SAW) scattering from single dots, periodic and locally disturbed two-dimensional dot arrays. By using the scanning acoustic force microscope (SAFM), SAW fields of arbitrary polarization can be imaged with submicron spatial resolution and sub-Å wave amplitude sensitivity. The influence of a wavelength-sized single dot on SAW diffraction is studied. Forward- and back-scattered wave components can be imaged by insonifying the dot with a pump and a probe beam under different angles. SAW diffraction images of a regular dot array reveal a wavefield that is localized around the dots. In case of a disturbed scattering array, the localized SAW pattern vanishes in the vicinity of the distortion.

Abstract:

We present an experimental method for the high-resolution imaging of the excitation and propagation of surface acoustic waves (SAWs) on anisotropic piezoelectric substrates. By employing a scanning acoustic force microscope (SAFM), we are able to image acoustic waves that are excitable by a single circular electrode pair source through the mixing with well-defined reference plane waves. We show amplitude and phase images of the point-source wave field, containing the angular dependence of the phase velocity of these modes, as well as their electromechanical coupling strength. The SAFM allows easy access to acoustic material properties, which are important for the design of commercial SAW devices. © 2001 American Institute of Physics.

Abstract:

We used multimode scanning acoustic force microscopy (SAFM) for studying noncollinearly propagating Rayleigh and Love wave fields. By analyzing torsion and bending movement of SAFM cantilever, normal and in-plane wave oscillation components are accessible. The SAFM principle is the down-conversion of surface oscillations into cantilever vibrations caused by the nonlinearity of the tip-sample interaction. Through mixing of complementary oscillation components, phase velocities of crossed Rayleigh waves on GaAs and crossed Rayleigh and Love waves on the layered system SiO2/ST-cut quartz were obtained simultaneously. Now, it is possible to investigate elastic properties of submicron areas through multimode SAFM measurements. Finally, we present mixing experiments of four SAWs on GaAs and discuss the various influences on the measured SAFM amplitude and phase contrast.