Professor Thorsten Hesjedal FInstP

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.

Abstract:

The intrinsic stress of the Stranski-Krastanov system Ge/Si(001) was investigated in the range 700 1050 K. Characteristic stress features indicate that the relief of the misfit strain proceeds mainly in two steps: (i) by the formation of 3D islands on top of the Ge wetting layer and (ii) via misfit dislocations in larger 3D islands and upon their percolation. The temperature dependence of strain relief by 3D islands as well as their nucleation and growth behavior support a kinetic pathway for 3D islanding. © 1998 The American Physical Society.

Abstract:

In this paper we report the observation of surface acoustic waves using a scanning tunneling microscope (STM). As the STM's control electronics has a bandwidth limit in the kHz range, SAWs at typical frequencies of MHz to GHz cause a loss of contrast which can be clearly seen on an atomic scale. In order to access the amplitude and phase of a SAW, we introduced a heterodyning type STM, the scanning acoustic tunneling microscope (SATM). Contrary to the STM technique, the SATM measures snapshots of the state of oscillation. On the nanometer scale, two contributions to the phase and amplitude contrast are discussed. First, the SAWs phase delay gives a mainly linear dependence on the distance of the source. Second, the atomic oscillation trajectories within the SAW lead to a signal contribution that is made up of the shape of the oscillation trajectory and the local topography. On an atomic scale where the influence of the phase delay on the contrast can be neglected the oscillation trajectories of single surface atoms are studied. Finally, the atomically resolved phase and amplitude images are compared to simulated data.

Abstract:

This paper reports first steps towards the determination of elastic constants with submicron lateral resolution. The experimental phase velocity dispersion data were obtained on a micron scale using scanning acoustic force microscopy. The minimum of the corresponding error field is only weakly localized, thus giving a large error for the elastic constants. The localization can not be increased by using more of data points. In order to decrease the elastic constant's error, a Love mode is additionally regarded. However, the error field crossing is in this case not leading to a significant increase of the accuracy. We propose the inclusion of further surface guided modes.