Scanning Tunneling Microscopy and Photoelectron Tunneling on Cesium

Abstract

This work focuses on the extraordinary low temperature system 'liquid helium on cesium'. This system forms a unique playground for physicists throughout the world, aiming to investigate the physics of both static and dynamic wetting phenomena, such as first order wetting transitions, prewetting, contact line pinning, and contact angle hysteresis. These various possibilities and the system's inherent properties such as chemical purity and the simplicity of the adsorbent, make adsorbed helium on cesium an ideal model system for the physics of wetting in general.However, there are a few unknown parameters complicating this system remarkably. One of them is the surface roughness of low temperature quench-condensed cesium films, which turned out to hugely influence the wetting properties of the system. For this purpose, scanning tunneling microscopy investigations of cesium films were conducted, leading to a deeper understanding of the growth of low temperature quench condensed cesium.Furthermore, up to now little is known on the 'non-wetting' helium thin film existing below the wetting temperature. For its investigation, tunneling of photoemitted electrons was already used as a probe. However, the mechanism of electron tunneling and electron backscattering by gas atoms was not understood in detail, leading to a broad spectrum of interpretation possibilities for the obtained photoelectron measurements. Therefore, a complete theoretical description of these phenomena is presented for the very first time. Experimental observations of both gas backscattering and electron tunneling obtained within this thesis are in very good accordance with the developed theory.