R.C.G. Leckey

Is there a universal mean-free-path curve for electron inelastic scattering in solids?

Abstract On the basis of a recent modification to dielectric theory, it is shown that the mean free path for inelastic electron scattering in a wide range of materials is described by a formula giving a dependence on electron energy of the form AE 0.75 where A is, however, sample-dependent.

Al2O3 prepared by atomic layer deposition as gate dielectric on 6H-SiC(0001)

Al2O3 films were deposited as alternative gate dielectric on hydrogen-terminated 6H-SiC(0001) by atomic layer chemical vapor deposition and characterized by photoelectron spectroscopy (PES) and admittance measurements. The PES results indicate an abrupt interface free of significant Si–suboxide contributions where the Al2O3 layer is connected to SiC by bridging oxygen atoms. The admittance measurements yield an interface state density which is lower than that of the thermally formed oxide and show in particular no increase toward the conduction band edge. Furthermore, a nearly symmetrical band alignment of Al2O3 on 6H-SiC with offsets of 2.2 and 1.8 eV is determined for the valence and conduction bands, respectively. This makes Al2O3 a serious competitor to thermal oxides as gate insulator in SiC devices.

An analytical expression for the calculation of electron mean free paths in solids

Abstract A simple analytical expression for the calculation of the inelastic-scattering mean free path for electrons in free-electron-like metals has been derived on the basis of a dielectric formalism. Good agreement with experimental data for energies greater than 200 eV has been demonstrated. By extending the concept of a one-mode excitation spectrum, an analogous formula applicable to semiconductors, insulators and non-free-electron-like metals has been derived which also compares well with experimental data.

An Analysis of the Transmission Properties of Spherical Electrostatic Electron Spectrometers

A detailed analysis of the transmission properties of low‐energy spherical electrostatic electron spectrometers employing preacceleration or preretardation is presented, which shows that the transmission efficiency of such instruments is not necessarily related inversely to electron energy nor directly to analyzer pass energy. A prescription, which enables observed spectra to be corrected over a wide energy range for intensity variations resulting from instrumental effects, is provided, and a detectable shift (≤ 0.1 eV) in the apparent position of electron lines under certain conditions is predicted. The theory is applied to the design and performance of two spherical photoelectron spectrometers employing ultraviolet and soft x‐ray sources. The analysis may readily be extended to other forms of electrostatic spectrometers employing preacceleration or preretardation.

Electronegativity as a unifying concept in the determination of Fermi energies and photoelectric thresholds

Abstract The method proposed by Nethercot for the determination of the Fermi energies and photoelectric thresholds of simple binary compounds has been successfully applied to some AB 2 compounds and metals.

Recent developments in electron energy analysers

Abstract Recent developments in the design of electrostatic analysers for the analysis of charged particles are reviewed. Emphasis is placed on design innovations which permit multidetection in terms of energy and/or angle of acceptance and on the use of position sensitive detectors in conjunction with traditional analyser designs.

The electronic structure of the valence bands of solid NH3 and H2O studied by ultraviolet photoelectron spectroscopy

Abstract The results of a photoelectron study using ultraviolet 40.81 eV photons (UPS) of the outermost bands of the molecular solids NH 3 and H 2 O are reported. The binding energies, the energy separation, the band widths and the branching ratio of the two outermost bands of solid NH 3 are found not to be significantly different from the 3a l and 1e molecular orbital states of the gaseous NH 3 UPS spectrum. This implies that hydrogen bonding has not produced any significant change in the electronic structure of the valence bands of solid NH 3 . Because of a much smaller intermolecular hydrogen bond length in solid H 2 O compared to that in solid NH 3 , the hydrogen bond does, however, produce a significant change in the valence bands of H 2 O on solidification, and because of the orbital geometry it predominantly affects the 3a l molecular orbital state.

Initial Stages of the Graphite-SiC(0001) Interface Formation Studied by Photoelectron Spectroscopy

Graphitization of the 6H-SiC(0001) surface as a function of annealing temperature has been studied by ARPES, high resolution XPS, and LEED. For the initial stage of graphitization – the 6√3 reconstructed surface – we observe σ-bands characteristic of graphitic sp2-bonded carbon. The π-bands are modified by the interaction with the substrate. C1s core level spectra indicate that this layer consists of two inequivalent types of carbon atoms. The next layer of graphite (graphene) formed on top of the 6√3 surface at TA=1250°C-1300°C has an unperturbed electronic structure. Annealing at higher temperatures results in the formation of a multilayer graphite film. It is shown that the atomic arrangement of the interface between graphite and the SiC(0001) surface is practically identical to that of the 6√3 reconstructed layer.

Design criteria for an angle resolved electron spectrometer of novel toroidal geometry

Abstract A charged particle analyser based on the use of polar trajectories in a toroidal sector is described in which a large number of particle emission angles are detected simultaneously. An analysis of the trajectories of particles in this class of analyser is presented and we develop transfer matrices which enable the imaging properties of such devices to be determined analytically. Expressions for the axial and radial magnification and for the energy resolving power are also derived. The analysis and the derived properties are compared with a numerical simulation and with all available published data.

Surface chemical shifts and photoelectron diffraction in CoSi2

An angle resolved study of the Si(2p) photoelectron line from bulk‐grown CoSi2(111), (100), and (110) surfaces has been performed using synchrotron radiation. A surface shifted component has been observed from annealed (111) and (100) faces, the surface/bulk intensity ratio being a strongly modulated function of polar emission angle and of photoelectron kinetic energy. Surface emission has been found to be significantly stronger from (111) faces than from (100) faces. We adopt a model in which the (100) face is terminated in a single Si layer, whereas we suggest that in the (111) surface, two Si layers exist above the first layer of Co atoms, thereby forming a Si (111)‐like template for the further growth of epitaxial Si. We consider that the interfacial Co atoms are sevenfold coordinated. Fractured CoSi2(111) surfaces are found to exhibit no surface Si.