The Solid State Physics GroupExperimental Physics

Chalmers University of Technology and Göteborg University

Figure 1. A STM image of the surface of NaVSe2.

In a nanowire the electrical conductance is quantized. So far this phenomenon has been studied dynamically by observing the decay of the current as a contact is broken. The main technical interest is to be able to control the quantized conduction in a wire with external static electric or magnetic fields or electromagnetic radiation.Contact persons: Professor Lars Wallden, email: wallden@fy.chalmers.seHåkan Olin, email: f4aolin@fy.chalmers.se

INFRARED SPECTROSCOPY OF MOLECULES AND ATOMS ON METAL SURFACESHow is a gas phase molecule affected when it is adsorbed on a metal surface and how does this molecule interact with other molecules, with chemisorbed atoms and substrate excitations? We use infrared light to excite vibrations in the system and as the vibrational modes are directly influenced by changes in the electronic bonds, it could be said that if we understand the properties of all vibrational modes we have also described the adsorption system.The group has recently bought a "state of the art" Fourier transform infrared (FTIR) spectrometer and with some special optics and careful tuning we probably have the most sensitive setup in this field of surface science.

As the first group we are presently studying oxygen atoms, alone or involved in surface reac-tions. Contact person: Roger Ryberg, email: ryberg@fy.chalmers.se

MICROMAGNETISM AND NANOMETRE-STRUCTURES

We study thin films, two dimensional arrays of magnetic particles prepared by electron lithography and cluster films. Our aim is to gain knowledge about the fundamental physical phenomena in magnetism, some of which are crucial in magnetic materials for applications.* Which factors determine how the magnetization is divided into domains? * By what processes and how fast can the magnetization in a domain change its direction? * What size should a particle have in order to comprise one single domain ? * How can the interactions between single particles be controlled ? * How densely can information be stored in a magnetic medium?We try to find answers to the questions by measuring macroscopic magnetization, studying domain structures in a Magnetic Force Microscope, MFM, and making micromagnetic model calculations. Contact person: Maj Hanson, email: maj.hanson@fy.chalmers.se

ELECTRON STRUCTURE OF SURFACES AND INTERFACES The theoretical subgroup have two major projects running at the moment. One project is a theoretical investigation of the properties of ultrathin alkalie metal overlayers on metal surfaces. We want to improve the understanding of the fundamental properties of quantum well states confined within these overlayers. Presently, we are trying to characterize the structure and electron structure of these systems by first principle calculations. We are also working with simple models to describe the dynamics of the photoemission process of electrons from the overlayers. This work is performed in close contact with experiments performed within the group. In the future, quantum size effects of island structures on surfaces is of interest in combination with STM and photoemission experiments.

Fig. 4. The relaxed non-polar ZnO surface.

The second project aims at an understanding of the properties of grain boundaries. One interesting phenomenon which is believed to be connected to grain boundaries is the strong non-linear voltage/current behaviour in varistors. Here, the focus is set on the electron structure of the grain boundaries in ZnO, which is a common base material in varistors. The electron structure is investigated by first principle calculations, and the conduction properties within the polycrystalline material are simulated by model calculations. In this project we collaborate with experimental groups at Uppsala university and KTH in Stockholm.Contact person: Bo Hellsingemail: hellsing@fy.chalmers.se

FILMS, DOTS and WIRES.Ultra-thin metal films, nanowires and small metal particles are presently the most interesting objects studied in solid state physics. Confinement leads to quantized electron and phonon states and size- dependent properties. This provides new and unique information which improves the understanding of basic phenomena in solids. From a practical standpoint these prop-erties are of interest for the development of a new class of metal based microelectronic components for the information industry. For some of these components, called spinonies, the properties depend not only on the charge of the electron, but also on the spin. We use pho-toemission tostudy the electron structure of valence electrons in thin films and dots. Scanning probe microscopy is used to get information about the local electronic structure and atomic order at the surface. The level structure is used to monitor how thin a film grows on the substrate. For device engineering this is of critical interest, since the thickness has to be controlled within the accuracy of one atomic layer. Apart from this, the energy, width and lineshape observed for the quantized valence electron states provide new means of getting information of fundamental interest i.e. dispersion of valence electrons, electron-phonon and electron-electron interactions. It also provides information about the photo-emission process itself, which 100 years after its discovery is still not well understood.

Fig. 3. A MFM picture of small Fe particles.

Fig 2. The FTIR spectrometer.