P. O. Nilsson

Appearance potential spectroscopy of simple metals

Abstract The APS spectra of Al, Mg, and Be have been measured. Good correlations to soft X-ray absorption spectra and density of states calculations are found. Plasmon satellites have been observed in Mg and Be. Edge singularities are detected in Al and Mg.

Experimental Verification of Optically Excited Longitudinal Plasmons

Anomalous optical absorption is observed in thin Ag films just above the bulk plasma frequency. The result is interpreted as excitation of longitudinal plasmons, an effect which is normally neglected when discussing optical properties. The dispersion relation of the plasma wave is obtained from the data.

Photoemission studies of the band bending on MBE‐grown GaAs(001)

The band bending on GaAs(001) surfaces prepared by molecular beam epitaxy (MBE) have been studied for n‐ and p‐type materials. Surfaces with c(4×4), c(2×8), and (4×6) reconstruction ranging from As to Ga rich have been investigated. The surface symmetry was determined by reflection high energy electron diffraction (RHEED) and the position of the valence band maximum relative to the Fermi level was measured using angle resolved UV photoelectron spectroscopy (ARUPS) at normal emission. The position of the Fermi level relative to the valence band maximum was found to be ∼0.7 eV for n‐type and ∼0.5 eV for p‐type material, with a slightly increasing trend in going from Ga‐ to As‐rich surfaces. For the (4×6) reconstructed n‐type samples the growth termination method was found to have a significant influence on the band bending. The results obtained here are in very good agreement with previous measurements of the Al–GaAs(001) Schottky barrier height indicating that the electronic properties of this junction are...

The electronic structure of In- and As-terminated InAs(001) surfaces

Abstract The InAs(001) 2 × 4 and 4 × 2 surfaces have been investigated by angle-resolved photoemission. The X 3 and X 5 points were found to be located 6.0 and 2.7 eV below the valence band maximum, respectively, and the dispersion of bulk bands along the Г-X direction in the bulk Brillouin zone were well described by a theoretical calculation. From angle-resolved valence band spectra measured along the high symmetry directions [110] and [110], three surface induced states were identified on both the InAs(001)4 × 2 and the InAs(001)2 × 4 surface.

Thermal effects in UV photoemission from Cu(110)

Abstract The temperature dependence of UV photoemission intensities from Cu(110) was studied in both mirror planes. Strong variations in the temperature dependence was found as the emission angle was changed, in disagreement with simple kinematical theory. These variations are different for different mirror planes, but similar for different d-band peaks in the same mirror plane. These findings raise questions about the importance of the wave-vector in connection with thermal effects. The temperature sensitivity is expected to increase with increasing emission angle due to enhanced surface vibrations, but in the case of emission in the ΓLUX plane the increase was qualitatively reproduced by “time-reversed LEED” calculations without accounting for enhanced vibrations. The measured thermal sensitivity was however considerably larger than the calculated. Earlier results from Cu(111) were found to be consistent with the results presented here, and a comparison gave some support to the importance of surface effects.

Temperature dependence in UV photoemission from Cu(111)

Abstract Angle-resolved UV photoemission from Cu(111) has been measured for various emission angles in the temperature range of 296–685 K. Various theories in the literature, based upon a kinematical approach, were found to be inadequate for a description of the experimental data. Instead we have applied a recent model by Pendry and Larsson, stressing the contribution from multiple scattering of the hole. A modified phonon spectrum in the surface also has to be included.

Mapping the excited-state bands above the vacuum level with VLEED: principles, results for Cu, and the connection to photoemission

Experimental photoelectron spectra are usually interpreted using rather crude approximations for the upper states into which the electrons are excited. Better knowledge about these excited states could substantially improve the accuracy of valence band mapping by photoelectron spectroscopy. We here demonstrate that VLEED measurements are ideally suited for accurate determination of the desired upper states. This is illustrated by model calculations including absorption and self-energy corrections. The close correspondence between so-called irregularity points of the excited-state bands and the total electron reflectivity is established, which opens up the possibility for direct mapping of irregularity points by comparison with experimental VLEED spectra, and for fitting of the whole excited-state bands between these points. The proposed scheme is finally used to determine the excited-state bands of Cu along from measurements on Cu(111).

Momentum selectivity and anisotropy effects in the nitrogen K-edge resonant inelastic x-ray scattering from GaN

High-resolution soft x-ray emission and absorption spectra near the N K -edge of wurtzite GaN are presented. The experimental data are interpreted in terms of full-potential electronic structure ca ...

A Simple Apparatus for Studies of UV-Bremsstrahlung

The basic principles of a simple apparatus for efficient recording of Bremsstrahlung in the UV-range is outlined. The radiation is analyzed with the use of a bandpass filter which is composed of a VUV window and a photocathode. The electrons from the photocathode are counted with a channeltron. Spectra of polycrystalline W obtained with LiF and CaF2 windows are reported.

Appearance Potential Spectra of the Alkaline-earth Metals Ca, Sr and Ba

An apparatus for measurements of appearance potential spectra in the 20-2 000 eV and 10-10 torr range has been constructed and tested. The total resolution is found to be about 0.8 eV. Spectra for different core levels of Ca, Sr, and Ba as well as of their oxides have been measured. The data are discussed in terms of localized, unoccupied electronic states. Comparisons are made with other types of experimental data and with models involving the (local) density of states. For Ba complications arise due to the very localized 4f states, but the results can be explained if the whole two-electron-one-hole system is taken into account.