Jerzy J. Czyżewski

Slow-electron inelastic scattering effects in a tungsten crystal

Abstract A method to study the density-of-states function by means of a CMA spectrometer is proposed which takes into account the diffraction effects of the inelastic-scattering electrons. The underlying principles of the method as well as its experimental verification for the case of the (001) single face of a tungsten crystal are presented. The experimental results are shown in the form of a set of the EELS spectra measured as a function of the primary electron energy, Ep, which was varied in the range from 30–100 eV. Taking into account the diffraction effects the energy loss peaks have been correlated with inter- and intra-band excitation energies based on the theoretical results published by N.E. Christensen and B. Feuerbacher [Phys. Rev. B 10 (1974) 2349].

An ILEED study of the density-of-states function of tungsten

Electron energy loss spectroscopy (EELS) and inelastic low-energy electron diffraction (ILEED) have been combined to study the density-of-states (DOS) function in tungsten. The EELS spectra measured as a function of the primary electron energy Ep (Ep < 100 eV) by means of a CMA spectrometer are interpreted in terms of the angular-resolved EELS taking into account the electron diffraction phenomena. As a result, we could correlate the EELS spectrum measured at a particular value of Ep with the one-dimensional DOS function. In addition, the LEED intensity theory, which we used in this work, has permitted us to estimate whether the correlation should be made with the surface-localized DOS (i.e. SDOS) or the bulk DOS (i.e. BDOS). Our experimental ILEED results are in good agreement with the theoretical DOS function published by Christensen and Feuerbacher [Phys. Rev. B 10 (1974) 2349]. In particular the energy gap in the theoretical electron structure along the [110] direction has been confirmed experimentally.

Investigation of the oxidized (001) tungsten surface by means of ILEED

Abstract Inelastic low energy electron diffraction (ILEED) effects have been applied to investigate the initial stages of oxidation on a (001) oriented single tungsten crystal. The electron energy loss spectra (EELS) have been measured as a function of the primary electron energy, E p . The energy was kept within the range: 45 eV E p To show the diffraction effect after loss we have used the kinetic model. The electron intensity, I = I ( E ), integrated over a ring input slit of a CMA, has been calculated as a function of the kinetic energy. The calculation has been performed in the k vector representation. The experimental and the theoretical results have been compared and shown to be in quantitative agreement with each other. A set of EEL spectra measured as a function of E p for the tungsten surface covered with a monolayer of oxide has shown the diffraction effect which was adequate to a (2 × 1) structure of an overlayer. As a result of the band transition investigation an agreement with some features of electronic structure of WO 3 has been found. The peaks at 4.0 eV and 7.2 eV observed in experimental EEL spectrum at E p = 55 eV are also present in a simulated EEL spectrum based on the density-of-states (DOS) function calculated for WO 3 .

The role of inner shell excitations in ESD of oxygen ions from a nickel oxide surface

Abstract A nickel (110) surface is oxidized and bombarded by low energy electrons. The yield of oxygen ions as a function of electron energy (24–90 eV) is observed. Onsets are seen at 30 and 35.5 eV. The desorption of positive oxygen ions cannot be explained by existing models. Inner shell excitations are believed to play a role. Part of the results can be explained by inner shell excitations accompanied by multi-electron excitations.

The influence of the electron-phonon scattering on the total energy distribution of field emitted electrons from tungsten

Abstract The total energy distribution (TED) of field emitted electrons has been measured for [012] direction of tungsten monocrystal in temperature region from 78 K to 950 K. To compare measurements with the free electron (FE) theory the parameters of FE equation of TED have been calculated by extrapolation of experimental results to the zero temperature. The explanation of obtained results has been proposed, taking into account the electron scattering phenomena of electrons supplied to the surface during the emission. Characteristic features of s→ d and s→ s scattering in transition metals described by Motts theory have been indicated by TED curves for the [012] direction. The Nottingham effect measured for [012] has been discussed as well.

Efficiency of the secondary emission from a (0 0 1) Ag surface

Abstract The true secondary-electron-emission efficiency from an Ag (0 0 1) surface in a take-off direction of 42.30° has been measured as a function of the primary electron energy, Ep. Applied procedure of the measurement and the processing data have related the true secondary-emission to the factor which includes the contribution of the primary current and the overall backscattering fraction. The measurements cover the energy range of Ep from 160 to 600 eV .

On some modification of the Mo(011) surface electronic structure by an oxide monolayer

Abstract Electron energy loss spectroscopy (EELS) has been used to investigate the electron interband transitions in a (011)Mo crystal covered by an oxygen monolayer. The paper continues the presentation of experiments in which the authors try to verify surface-localized electronic structures. In the case of clean (011)Mo studied in our previous paper we had applied the inelastic low energy diffraction effects in EELS analysis due to a well defined crystal structure of the surface. The effects increase the signal to noise ratio and thus the inter-band transitions can be detected at primary electron energies below 100 eV. It has been found that the EEL spectra measured for the oxidized (011)Mo plane and measured for the clean surface at Ep = 45 eV show significant differences from each other. A theoretical simulation of the EEL spectrum based on the density-of-states function published by other authors for molybdenum oxide shows a qualitative agreement with the experimental result.

Investigations of the band transitions in ruthenium (0001)

Abstract Inelastic low energy electron diffraction (ILEED) effects have been found in electron energy loss spectroscopy (EELS) of the ruthenium (0001) surface. In the experiment a cylindrical mirror analyzer (CMA) has been used. The EEL spectra were measured as a function of the primary electron energy E for E

The Field Emission Energy Distribution (FEED) study of electron interactions in tungsten

Field Emission Energy Distributions (FEED) have been measured along the [001], [016] and [013] directions of a tungsten crystal within the temperature range 78 < T < 950 K. Both electron-phonon interactions and band structure effects have been considered as a function of the crystallographic orientation. Measurements over a wide range of temperature have been interpreted in terms of both electron-d hole and electron-phonon interactions. The comparison of measurements along [001], i.e. the emission mainly from the d band with those previously published along [012], i.e. the emission mainly from the s band, is consistent with the postulated s → d transitions directly. Under conditions in which electron-phonon scattering occurs, the relation of FEED to the Nottingham effect has been investigated. In the light of electron transport phenomena in tungsten the calculation of the inversion temperature seems to require a new theoretical procedure.

Inelastic scattering of electrons at metal surfaces

Abstract We present experimental electron energy loss spectra (EELS) for a clean Mo(011) surface. The incident energy ranges from 30 eV to 100 eV and the energy loss of the backscattered electron ranges from about 2 eV to about 10 eV. We propose an interpretation of the EEL spectra on the basis of an approximate theory of the scattering process in an attempt to clarify the determining factors of this process.