Soft X-ray Appearance Potential Spectroscopy Research Articles

Mossbauer and soft X-ray appearance potential spectroscopy of iron-nickel-boron metallic glasses

Mossbauer spectra and soft X-ray appearance potential spectra from (Fe0.5Ni0.5)1-xBx metallic glasses for 0.16<or=x<or=0.26 are reported. Mossbauer and magnetic data are determined by the occupation difference between majority and minority subbands. Appearance potential spectra, on the other hand, reveal the total density of unoccupied states. From a combination of the two sets of data for iron the authors derive the change of subband occupation as a function of boron concentration. As a result they find charge transfer not only from boron to empty minority iron states but also from majority to minority states. Unoccupied d states of nickel do not show any change as a function of boron content.

Soft X-ray appearance-potential spectroscopy studies of DyFe 2 and ErFe 2 intermetallics

The soft X-ray appearance-potential spectra (SXAPS) of the M 4,5 levels of Dy and Er and the L 2,3 levels of Fe in pure metals and their intermetallics DyFe 2 and ErFe 2 have been obtained in the energy range of 700–1500 eV. SXAPS probes the binding energies of the core levels and the distribution of local unfilled conduction-band states. Both the constituents of DyFe 2 show negative shifts with respect to the pure metals while those of ErFe 2 show a negative shift for Er and a positive shift for Fe. The widths of the Dy and Er peaks increase and that of the Fe decreases on alloying. The results are interpreted in terms of the Fermi level changes and the charge transfer from the rare earth to Fe. The discrepancy in Fe chemical shifts has been correlated to the electronic specific heat capacity coefficient reported for these intermetallics.

Soft X-ray appearance-potential spectroscopy studies of DyFe 2 and ErFe 2 intermetallics

Soft X-ray appearance-potential spectroscopy studies of DyFe 2 and ErFe 2 intermetallics

Appearance potential spectroscopy of CuZr and CuTi metallic glasses

The local density of empty electronic states at the Cu sites in CuZr and CuTi has been derived from soft X-ray appearance potential spectroscopy (SXAPS) on glassy Cu 60Zr 40 and Cu 40Ti 60 samples. An energetically narrow d-like density of states is found just above the Fermi level. Results are discussed in terms of d-band hybridization.

Correlation of selected core-level spectroscopies

Spectral characteristics representing the distribution of unoccupied conduction-band states in the 3 d transition-series metals Fe, Co, Ni and Cu, obtained using soft X-ray absorption (SXA), bremsstrahlung isochromat (BI) and characteristic isochromat (CI) methods, are related mathematically to those found in soft X-ray appearance-potential Spectroscopy (SXAPS) on the basis of the one-electron band approximation. These mathematical relationships are used to compute SXAPS spectra from reported experimental data obtained by the SXA, BI and CI methods. For the metals considered, the correlations between the computed and experimental SXAPS spectra are found to be good. The observed discrepancies are attributed to differences in the selection rules of the excitation processes, to the effect of the core vacancy on the final state, and to many-body phenomena which are not included in the simplified one-electron band model.

Soft X-ray appearance potential spectroscopy of the lanthanide rare earths

Soft X-ray appearance potential spectroscopy (SXAPS) exploits the sudden changes in the fluorescent yield associated with the thresholds for the electron excitation of core states. Inflections on the yield curve, easily enhanced by differentiation, provide information on the electronic properties of the target material. For the rare earths, the M 5, M 4 spectra are multipeaked and unusually intense. The excitations are localized involving atomic f levels relatively unaffected by atomic environment. The spectra are attributed to couplings between the incident electron, the excited electron and the resultant hole which leads to a resonant interaction that splits and intensifies the lines. The present status of SXAPS will be presented concentrating on the interpretations given to specific experiments.

Surface TiH n as the catalytically active species for the hydrogen absorption by TiFe; a SX-APS investigation supplemented by AES

The interaction of hydrogen with the surface of previously cleaned TiFe samples was investigated by means of Soft X-Ray Appearance Potential Spectroscopy (SX-APS) and Auger Electron Spectroscopy (AES). The access of oxygen (air) was carefully prevented by performing all experiments “in-situ” in an UHV-chamber. At about 800°C the hydrogen interaction with the TiFe surface leads to extensive Ti segregation. As observed by SX-APS, iron is displaced by titanium on the whole surface of the sample (about 1.5 cm 2). From AES depth profiles the Ti overlayer is estimated to have a thickness of about 100 monolayers. In this region Fe is completely absent. No enrichment of Fe beyond this region could be detected; the Fe concentration increases monotonously from zero to the bulk value. From these results it is obvious that the hydrogen absorption/desorption of TiFe is catalytically activated by Ti species rather than by Fe species. The chemical state of the surface is discussed.

The density of unoccupied electronic states in copper

The density of unoccupied electronic states in Cu has been measured employing soft X-ray appearance-potential spectroscopy (SXAPS). The L III le

The oxidation of nickel: A study of empty electronic states by inverse photoemission and soft X-ray appearance potential spectroscopy

Soft X-ray appearance potential spectroscopy (SXAPS) and inverse photoemission (IPE) have been employed to study the oxidation of a polycrystalline nickel sample. Both methods probe empty electronic states. The present results when supplemented by UPS data establish an experimental determination of the NiO band structure consistent with theoretical models of localized and itinerant states.

The oxidation of nickel: A study of empty electronic states by inverse photoemission and soft X-ray appearance potential spectroscopy

The oxidation of nickel: A study of empty electronic states by inverse photoemission and soft X-ray appearance potential spectroscopy

Isochromat and SXAPS studies of empty electronic states in chromium, iron and nickel

The density of unoccupied electronic states in Cr, Fe and Ni has been measured employing bremsstrahlung isochromat spectroscopy (BIS) and soft X-ray appearance potential spectroscopy (SXAPS). The LIII core levels were used for the SXAPS measurements. BIS data was taken in the ultraviolet region, the spectrometer energy being 9.7 eV. BIS spectra, after proper correction for electron-hole pair production prior to the radiative process, show encouraging agreement with theoretical calculations and with the density of states derived from the corresponding SXAP spectra by recently developed deconvolution techniques.

Soft—X-Ray Appearance Potential Spectroscopy of Metallic Glasses

Soft—X-Ray Appearance Potential Spectroscopy of Metallic Glasses

Apparatus for the direct measurement of the internal energy of heterogeneous reaction products

An instrument to measure the rotational and vibrational energies of heterogeneous reaction products has been constructed. Reactant atoms pass through a membrane made of the material being studied. After recombination and desorption occurs, the product gas is analyzed via either electron beam or laser-induced fluorescence. Surface composition is monitored by soft x-ray appearance potential spectroscopy. Results for nitrogen molecule desorption from clean, polycrystalline iron are presented in order to illustrate the capabilities of the apparatus.

Soft x-ray appearance potential studies of 59Pr, 65Tb, 67Ho, and 68Er

Soft x-ray appearance potential spectroscopy (SXAPS) investigations of rare-earth metals have been recently conducted by various researchers. Among these studies is one just published, Hua et al., in which it is claimed that no rare-earth metals with an even number of 4f electrons (e.g., 59Pr, 65Tb, 67Ho) has yielded any characteristic appearance potential spectrum. Contrary to this assertion, our data reveals significant results for M4,5 spectra of these metals. Also, the intensity of APS peaks in rare earths is shown to depend on the total number of 4f electrons rather than their odd or even character. Furthermore, the M5/M4 intensity ratios have been systematically investigated.

Soft x-ray appearance potential spectroscopy study of pure rare-earth metals with a sealed-off analyzer tube

A comparative study of the soft x-ray appearance potential spectra of various pure rare-earth metals has been carried out with a specially designed sealed-off analyzer tube. It is shown that for lanthanide elements with even number of 4f-electrons (except Eu) no spectrum is found in a region of accelerating potential from 50 to 1400 V. The most sensitive peaks are M5 (3d5/2) and M4 (3d3/2), which can serve as ’’finger prints’’ to identify the rare-earth metals. The ratio of the M5/M4 peak heights might be classified into three groups, according to their various values. Satellite peaks also exist, although no satisfactory explanation has yet been given. The purity of most samples is checked by a Mattauch–Herzog type mass spectrometer or by the proton-induced x-ray emission (PIXE).

Solid Surface Analysis using the Secondary Electron Yield Spectrum.

Auger electron appearance potential spectroscopy (AEAPS) apparatus for the study of solid state surfaces was constructed and the working conditions were extensively examined for surfaces of the 3d transition metals (Ti∼Ni). For the clean surface of polycrystalline Ti, the spectra of the first and second derivative signals were in good agreement with theoretical results obtained from the unfilled 3d binding state at Fermi energy EF. The spectra of Ti, Fe and Ni were obtained on both clean and oxidized surfaces at room temperature. The AEAPS and soft Xray appearance potential spectroscopy (SXAPS) spectra were compared on the same Mn and Co clean surfaces. Relative L3 AEAPS signal strengths were measured for clean 3d transition metal (Ti∼Ni) surfaces.

A simple appearance potential spectrometer

The design of a very simple appearance potential spectrometer is given. Its main part consists of a commercially available ionisation gauge. By suitably selecting the electrode potentials, the apparatus can be used for both Auger electron and soft X-ray appearance potential spectroscopy. Spectra of the grid material (Ni), of thoria evaporated from the cathode, and of some impurities can be obtained. Because the spectra reveal the electronic structure of solids in a very direct way, the experiment is well suited for teaching laboratories and lecture demonstrations.

The Density of Unoccupied Electronic States in Tantal

AbstractThe density of states in the unoccupied part of the conduction band of polycrystalline tantal is investigated using ultraviolet isochromat spectroscopy and soft X‐ray appearance potential spectroscopy (SXAPS). Density‐of‐state functions deduced from the two different measurements are quite similar and compare favourably to existing theoretical calculations.

AES and APS studies of the detection of Mn in low alloy steel

Comparative studies have been made of the detection of Mn in a low alloy steel containing 1.4% Mn using Auger electron spectroscopy (AES) and soft X-ray appearance potential spectroscopy (APS). Quantitative analysis can be made using both techniques, although in the case of AES, spectrum subtraction techniques have to be used to retrieve the Mn spectrum due to severe peak overlap with the Fe spectrum. Excellent quantitative agreement between AES and APS is found and it is demonstrated that care must be exercised to ensure that large electron current densities (> 2 mA/cm 2) are not used in acquiring data, otherwise significant surface segregation of Mn may occur.

Soft X-Ray appearance potential spectroscopy of C, N and O adsorbed on Cr, Mo and W

The 1s level soft x-ray appearance potential spectra of C, N and O chemisorbed on polycrystalline Cr, Mo and W surfaces have been observed. The adsorbate ls spectra show the following characteristic features in the chemisorption regime: (i) Cr: one single peak; (ii) Mo and W: a doublet structure. We tentatively assume that the doublet structure is due to a splitting in the antibonding levels of the surface complex. Oxidation of Mo and W at high temperature causes changes in the metal (Mo 2p 3 2 and W 3d 5 2 ) and in the oxygen 1s spectra as compared with the spectra obtained after room temperature adsorption of oxygen.