T. Strasser

Valence-band photoemission from the GaN(0001) surface

A detailed investigation by one-step photoemission calculations of the

Electronic band structure of gallium nitride: a comparative angle-resolved photoemission study of single crystals and thin films

\mathrm{GaN}(0001)\ensuremath{-}(1\ifmmode\times\else\texttimes\fi{}1)

How to Determine Fermi Vectors by Angle-Resolved Photoemission

surface in comparison with recent experiments is presented in order to clarify its structural properties and electronic structure. The discussion of normal and off-normal spectra, reveals through the identified surface states, clear fingerprints for the applicability of a surface model proposed by Smith et al. [Phys. Rev. Lett. 79, 3934 (1997)]. Especially the predicted metallic bonds are confirmed. In the context of direct transitions, the calculated spectra allow us to determine the valence-band width and to argue in favor of one of two theoretical bulk band structures. Furthermore, a commonly used experimental method to fix the valence-band maximum is critically tested.

OPTICAL POTENTIAL AND ESCAPE DEPTH FOR ELECTRON SCATTERING AT VERY LOW ENERGIES

Angle-resolved photoemission measurements on gallium nitride single crystals and epitaxial thin films with wurtzite structure were performed using synchrotron radiation. Calculated theoretical final state bands were used to determine the corresponding k vectors in reciprocal space using the direct transition model. We were able to identify several previously unobserved features including several surface states and transitions to non-free-electron final states. Significant differences in the surface electronic band structure between thin film and single crystal samples were observed. 2002 Elsevier Science B.V. All rights reserved.

Photoemission study of S adsorption on GaAs (0 0 1)

Angle resolved photoemission spectroscopy (ARPES) has been commonly applied to evaluate the shape of Fermi surfaces by employing simple criteria for the determination of the Fermi vector k_F parallel to the surface such as maximum photoemission intensity at the Fermi level or discontinuity in the momentum distribution function. Here we show that these criteria may lead to large uncertainties in particular for narrow band systems. We develop a reliable method for the determination of Fermi vectors employing high resolution ARPES at different temperatures. The relevance and accuracy of the method is discussed on data of the quasi two dimensional system TiTe_2.

Tuning dimensionality by nanowire adsorption on layered materials.

Abstract Electron spectroscopy at low kinetic energies, e.g., valence band photoemission with vacuum ultraviolet light, is sensitive to the fine structure of the electron damping, i.e., to the magnitude and energy dependence of the optical potential. The basis of this quantity is usually given by a semiquantitative analytical derivation together with empirical findings from the escape depth. Only recently the optical potential has been determined ab-initio via calculating the self-energy. Here, this approach is used to calculate the self-energy and from this the wave functions in the conduction band regime with scattering boundary conditions for the surface system. For the former, the GW approximation is applied. For the latter, algebraic solvers in the Laue representation have been used to solve the Schrodinger equation for arbitrary potentials. The wave function is investigated to extract physical quantities, like the angle and energy dependent escape depth, which are significant in discussing electron scattering.

Three-dimensional Fermi surface determination by angle-resolved photoelectron spectroscopy

Angle-resolved photoemission spectra have been calculated with the one-step model for S/GaAs(0 0 1) and compared with experimental distributions. The data are analysed in terms of the ideal 1 × 1 and, furthermore, of the reconstructed 2 × 6 surface which is assumed to be closest to the experimentally realized structure. Emissions are characterized by electronic structure terms such as energy bands and orbital composition, though partly also by geometric properties. In particular, the determination of the second layer as consisting of Ga atoms has been achieved because of the distinct differences in the theoretical spectra with S–Ga and those with S–As bonds.