Professor Thorsten Hesjedal FInstP

Abstract:

In this paper we present a new method that allows the measurement of the phase velocity of in-plane polarized SAWs with high spatial resolution. The capabilities of the scanning acoustic force microscope had to be extended by the analysis of torsional cantilever motion. A nonlinear coupling mechanism between in-plane oscillations and this movement could be found, that allows an mechanical mixing of in-plane SAWs. Phase velocity measurements of Love waves on the system Au/SiO2/ST-quartz are presented. A good agreement with theoretical predictions for the velocities could be found.

Abstract:

The intrinsic stress and morphology of the Stranski-Krastanow system Ge/Si(111) have been investigated at deposition temperatures of 700-950 K. In a broad range of intermediate temperatures, only one distinct decline of stress is observed at the onset of three-dimensional islanding. Supported by a recent transmission electron microscopy study, the results demonstrate that the strain of Ge/Si(111), where the substrate surface in contrast to Ge/Si(001) is the glide plane for dislocations, is relieved by incorporation and continuous rearrangement of dislocations during the island stage. © 1998 American Institute of Physics.

Abstract:

We present a scanning acoustic force microscope (SAFM) for the study of surface acoustic wave (SAW) phenomena on the submicron lateral scale. Until now, SAWs with in-plane oscillation components could only be studied effectively via nonvanishing out-of-plane oscillation contributions. By operating the microscope in lateral force mode, where both bending and torsion of the cantilever are detected, additional amplitude-dependent signals are found, which are due to the interaction with purely in-plane polarized surface oscillations. To demonstrate the capabilities of this type of SAFM, Love waves were studied on the surface of layers deposited on ST-cut quartz with SAW propagation perpendicular to the crystal X-axis. The phase velocity of the wave as well as the amplitude of a standing wave field was measured and compared to calculated values. © 1998 American Institute of Physics.

Abstract:

It is well established that the growth of Ge on Si(001) proceeds by Stranski-Krastanov mode, i.e. 3D islands ("hut" and macroscopic clusters) nucleate on top of a 3-4 ML thick pseudomorphic layer. Here, we present in-situ intrinsic stress measurements of Ge/Si(001) up to the film thicknesses at which the 3D islands percolate. From the film stress - and supported by AFM investigations - three stages of film growth characterised by different reliefs of the misfit strain can be discriminated: (1) the pseudomorphic layer-by-layer stage, (2) nucleation and growth and (3) coalescence of 3D islands. © 1998 Elsevier Science B.V. All rights reserved.