Janusz Krajniak

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 .

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 .

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

Decomposition of carbon-bearing compounds and their influence on methane formation in a lignite incubation experiment

Abstract Carbon-bearing compounds (glucose, sodium acetate, methanol, yeast extract, and nutrient broth) were added in different proportions to cultures to stimulate methanogenesis in a lignite incubation experiment. Their addition significantly influenced the isotopic composition of methane generated during the fermentation of lignite. Glucose was degraded mainly in the first 2 weeks of incubation, when the atmospheric air was present in the headspace and used for biomass growth. Sodium acetate, methanol, and, presumably, lignite were decomposed in the next phase, in which anaerobic conditions occurred. The simultaneous decomposition of sodium acetate and methanol (as single substrates or as a mixture) with lignite resulted in the formation of methane with δ13C(CH4) values typical for methyl-type fermentation. The identification of decomposed compounds in the mixture of sodium acetate and methanol was accomplished via isotopic analysis of carbon and hydrogen in the methane. The δ2H(CH4) values in the case of methanol biodegradation were characterized by a negative trend over time, in contrast to a positive trend observed when sodium acetate decomposed. This observation may help to identify a very good tracer for the determination of methane precursors during methyl-type fermentation.