Showing papers by "Hans-Gerd Boyen published in 1996"
TL;DR: In this paper, photoelectron spectroscopy of liquid silicon and germanium has been performed by using a new technique based on laser-pulse induced melting of sample surfaces and time resolved detection of the photoelectrons.
Abstract: Photoelectron spectroscopy of liquid silicon and germanium has been performed by using a new technique based on laser-pulse induced melting of sample surfaces and time resolved detection of the photoelectrons With this method it has, for the first time, been possible to observe the solid to liquid phase transition of silicon, an element with a vapor pressure in the liquid phase which is orders of magnitude higher than the acceptable value in standard photoemission Due to the identical experimental conditions during the characterization of the solid and liquid state, a direct comparison of photoelectron spectra can be made qualitatively as well as quantitatively This is shown in the two cases of silicon and germanium
7 citations
TL;DR: In this article, a method to perform photoelectron spectroscopy (PES) on systems at high temperatures and with a high saturation vapor pressure is presented, which consists of a time-resolved data acquisition following pulsed laser heating and melting of the sample surface.
Abstract: A method to perform photoelectron spectroscopy (PES) on systems at high temperatures and with a high saturation vapor pressure is presented. The basic concept consists of a time‐resolved data acquisition following pulsed laser heating and melting of the sample surface. With this technique it is possible to get access to samples under conditions which normally would not be compatible with the requirements of PES. A standard electron spectroscopy for chemical analysis spectrometer has been equipped with additional electronics to allow time‐resolved measurements. A small spot monochromated x‐ray photoelectron spectroscopy source is used for the core‐level spectroscopy and a modified gas discharge lamp for excitation of the valence band. The first results of valence‐band spectra taken with this method are shown for germanium and silicon and its feasibility even in core‐level spectroscopy is shown in the case of germanium.
5 citations
TL;DR: In this paper, the authors used dye laser pulses to melt the sample surface on a microsecond scale, starting at a temperature of the liquid sample just above the melting point (740 K), and obtained, for the first time, valence band spectra of an alloy at temperatures of up to 1620 K, distinctly above the vapour pressure limit of steady-state photoelectron spectroscopy.
Abstract: The solid - liquid - solid-phase transitions of a alloy have been investigated by means of the recently developed method of time-resolved photoelectron spectroscopy, using dye laser pulses to melt the sample surface on a microsecond scale. Starting at a temperature of the liquid sample just above the melting point (740 K), the laser pulse heating allowed us to obtain, for the first time, valence band spectra of an alloy at temperatures of up to 1620 K, distinctly above the vapour pressure limit of steady-state photoelectron spectroscopy. The photoemission results of the liquid at different temperatures are compared with data from the corresponding amorphous alloy, prepared by vapour condensation at liquid-nitrogen temperature. By increasing the temperature of the disordered phase, the Au 5d band is found to shift continuously toward a lower binding energy, showing a linear behaviour over the whole temperature range. Our measurements confirm earlier results obtained with conventional photoemission within a restricted temperature range. The results presented here clearly show the potential of the new technique to investigate the electronic structure of alloys at conditions under which standard photoemission experiments cannot be performed.
4 citations
TL;DR: In this paper, the Noziere−De Dominicis theory is used to calculate core line asymmetries from the partial electronic densities of states at the Fermi energy.
Abstract: Copyright (c) 1996 Elsevier Science B.V. All rights reserved. Core level line asymmetries for liquid Al, Ga, Ge, In, Sn and Bi have been determined by numerical analysis of XPS core level spectra using Doniach−Sunjic lineshapes. For the pure liquid metals, the asymmetry parameters a have been determined as: Al2p: 0.13, Ga3d: 0.11, Ge3d: 0.09, In4d: 0.12, Sn4d: 0.13 and Bi5d: 0.12. Noziere−De Dominicis theory is used to calculate core line asymmetries from the partial electronic densities of states at the Fermi energy. Good agreement is achieved for systematic changes in both parameters. Experimental Knight shifts of liquid metals are compared with theoretical values for s−p-metals. They support the theoretical s-electron density of states (DOSr data used for calculation. Furthermore a quantitative relation between asymmetry and total DOS at the Fermi energy is proposed to explain the observed increase of asymmetry in Ga upon melting: solid: a=0.06, liquid: a=0.11.
1 citations
TL;DR: In this paper, photoelectron spectroscopy was used to detect structure-induced minima in the electronic density of states at the Fermi level for the intermixed amorphous phases.
Abstract: Interface reactions were observed by means of photoelectron spectroscopy during the preparation of Au/Sn bilayers at 77 K. These reactions lead to ultra-thin (0.5–2 nm) amorphous layers with tunable stoichiometry, spanning the same range of compositions as found for the corresponding vapor-quenched amorphous Hume-Rothery alloys. In all cases, structure-induced minima in the electronic density of states at the Fermi level are observed for the intermixed amorphous phases. Since structure-induced minima are a characteristic feature of a Peierls system, the ultra-thin amorphous layers may be discussed as reflecting the transition from a nearly two-dimensional to an isotropic three-dimensional Peierls-distorted system.
1 citations
TL;DR: In this paper, the electrical resistance and the thermoelectric power of thin Au films on top of amorphous Sb films as a function of increasing thickness of the Au film were investigated.
Abstract: Our investigation of the electrical resistance and the thermoelectric power of thin Au films on top of amorphous Sb films as a function of increasing thickness of the Au film allows us to compare the data with those on amorphous films with increasing Au content. The comparison shows a substantial similarity of the low-temperature data as well as of the annealing behaviour. This gives additional support to the hypothesis of the formation of an amorphous phase at the interface in layered Sb/Au films. The thicknesses of those parts of the Sb film and the Au film which contribute to the formation of the amorphous interface are determined and agree well with data taken from photoelectron spectroscopy and resistance measurements during evaporation. The quantitative differences which exist in the concentration dependence of the electrical resistance and the thermoelectric power between the Sb/Au bilayers and the amorphous films are probably caused by the reduced geometry of the ultrathin interface.
1 citations
TL;DR: In this paper, the electronic structure of amorphous FexY100−x alloys (31 ≤ x ≤ 87) co-evaporated under UHV conditions has been investigated using photoelectron spectroscopic methods (UPS, XPS).
Abstract: The electronic structure of amorphous FexY100−x alloys (31 ≤ x ≤ 87) co-evaporated under UHV conditions has been investigated using photoelectron spectroscopic methods (UPS, XPS). The results are compared to calculations based on the local spin-density (LSD) approximation and a molecular dynamic modeling of the amorphous structure. The evolution of the valence band structure as a function of the alloy composition is discussed in relation to previously studied amorphous FexZr100−x alloys. A good agreement between the experimental spectra and the theoretical predictions is found in the Fe-rich regime. The discrepancy observed in Y-rich samples is attributed to a tendency for segregation of Y and Fe atoms, as indicated by the molecular dynamic simulations and small-angle neutron diffraction experiments.