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1.
The angular distribution of the Auger emission from Ni(100), Ni(100)c(2 × 2)-S, Al(001) and Al(110) has been studied by recording azimuthal and polar profiles for the nickel and sulfur MVV Auger peaks and for the aluminum LVV Auger peak. The character of the anisotropy is very different for the aluminum and nickel surfaces: the profiles are rather smooth for aluminum and present numerous sharp structures for nickel. Moreover when the sulfur overlayer is present, the nickel Auger peak anisotropy is strongly perturbed and the emission anisotropy of the sulfur Auger peak is found very important. 相似文献
2.
The L1L23V and L23VV Auger spectra of sputtered and annealed Si(100) have been measured and the transition density of states extracted. The line shapes for the two transitions differ, indicating the importance of matrix element effects. Whereas the L1L23V line shape closely resembles results of other measurements of the Si density of states, the L23VV line shows a strong emphasis on p-like states. 相似文献
3.
Auger electron spectra have been recorded when oxygen is adsorbed on a Ni(111) single crystal surface. For the coverage range θ < 1, an analysis of the plot of the peak to peak height (H) of the oxygen KVV (516 eV) transition versus the total number of molecules cm2? impinging on the surface (molecular beam dosing) shows agreement with the kinetic mechanism proposed by Morgan and King [Surface Sci. 23 (1970) 259] for the adsorption of oxygen on polycrystalline nickel films. In this coverage range, no energy shifts of the nickel or oxygen Auger peaks were recorded.At coverages θ > 1 (standard dosing procedure) shifts in the valence spectra M2, 3VV (61 eV) and L3M2, 3V (782 eV) of ?2.3 eV and ?1.8eV respectively are recorded at 1.4 × 10?2 torr-sec. Up to these coverages no shift of the L3VV transition (849 eV) is observed. A chemical shift of ?2.1 eV is recorded in the L3M2, 3M2, 3 Auger transition (716 eV) at 1.4 × 10?2 torr-sec.In the coverage range θ > 1, shifts in the energy of the oxygen Auger peaks are observed. At 5.8 × 10?3 torr-sec. the KVV (516 eV) and KL1V (495.2 ± 0.3 eV) transitions show shifts of ?1.5 eV and ?(1.0 ±0.3) eV respectively. No shift up to this coverage is recorded in the KL1L1 (480.6 ± 0.3 eV) transition. 相似文献
4.
The L23 Mg and L23 Al Auger spectra excited by helium-ion bombardment have been studied. These spectra essentially show an intensive peak interpreted in terms of L23 MM atomic-like and L23 VV transitions. By integration of this peak, the Auger emission cross sections were determined and their variations as a function of the incident particle energy were studied from a few keV up to 100 keV. These results have been compared to the values of the ionization cross sections calculated in a classical binary encounter approximation (BEA). One observed a good agreement for the aluminium target. For the magnesium, the discrepancy in the low energy range shows that, in those case, the electronic promotion in a molecular orbital model added at the electronic excitation due to the direct Coulomb interaction. 相似文献
5.
A comparison of Auger structures observed on the energy distributions of secondary electrons emitted from Mg and A1 solid targets bombarded by either light particles (H+ and He+) or heavy ions (Ne+, Ar+, …) is presented. With incident protons, it essentially appears a broad peak corresponding to a L23VV transition and a weak shoulder due to the surface and bulk plasmon excitation. The Auger structures obtained with heavy ions are richer and the peaks which compose it are sharper. Such atomic-like structures correspond to Auger transitions from excited (with one or two L23 holes) moving recoiling atoms. The experimental L23 Mg and A1 ionization cross sections were determined from Auger spectra. In H+?Mg (or A1) collisions our results are in good agreement with the theoretical values calculated in a PWBA model. In the case of heavy ion-target interactions, we compared the experimental measurements with ionization cross section calculations obtained in a Landau-Zener model. 相似文献
6.
Electron energy loss spectra of clean and oxygen-covered Ni(100) surfaces were observed with concomitant measurements of LEED, work function change, and Auger peak height ratio O(KL2, 3L2, 3)/Ni(L2, 3VV). The observed electronic transitions are interpreted on the basis of primary election energy dependence, and of comparison with the loss spectrum for a UHV-cleaved NiO(100) surface and optical data of Ni. The observed loss peaks at 9.1, 14, and 19 eV in the clean surface spectrum are ascribed to the bulk plasmon of the 4s electrons, the surface plasmon, and the bulk plasmon of the coupled 3d + 4s electrons, respectively, and the weak but sharp peak at 33 eV is tentatively attributed to the localized many-body effect in the final state. Three oxygen-derived peaks at 6.0, 8.0, and 10.3 eV in the low oxygen exposure region (?4 L) are ascribed to the O 2p(e) → Ni 3d, O 2p(a1) → Ni 3d, and O 2p → Ni 4s transitions, respectively. In the high oxygen exposure region (?50 L), the spectra become quite similar to that of the UHV-cleaved NiO(100) surface. The oxidation process consistent with LEED, Auger peak height ratio and work function change measurements is discussed. 相似文献
7.
Autoionization electron emission from nickel in NiTi, initiated by electron-beam excitation is reported. It is the first observation of such electron-excited Ni emission, and unlike the case of elemental nickel, the feature is distinctly resolved from the Ni M2,3VV Auger line. The measurements were done at temperatures corresponding to the CsCl-type phase of NiTi, and the emission intensity was found to depend critically on the annealing treatment of the sputter-cleaned sample.The appearance of Ni autoionization emission in Niti is attributed to changes in the distribution of the empty and filled d-states at the nickel sites on alloying with titanium. Emission energy shifts are estimated on the basis of reported theoretical band-structure calculations for NiTi. 相似文献
8.
The total energy distribution of electrons emitted from clean Cu(100) and oxygen covered surfaces is analysed. A primary electron energy of 400 eV enabled the investigation of characteristic losses (ELS), Cu MVV Auger transitions and true secondary electrons in a single spectroscopic run. Oxygen exposure up to 108 L at elevated temperature (~400 K) results in a Cu density of states (DOS) strongly affected by O(2p) electrons. The Auger lines of Cu, atomic-like for clean surfaces, reveal DOS effects after some 107 L oxygen exposure: all MVV transitions shift down by ~2 eV in spite of a fixed M23 level; the M23VV Auger line splitting is vanishing due to a broadened valence band maximum allowing the deexcitation of the final two-hole state of intraatomic transitions. Heating the oxygen covered crystal to 820 K is accompanied by the removal of much surface oxygen and an electronic state resembling an earlier oxidation state without DOS effects in the Cu Auger spectrum. 相似文献
9.
The angular distribution of Cu M2,3VV and Au N6,7VV Auger electrons from Cu and Au mono- and double layers on W(110) is measured with the goal of obtaining information on the contribution of the backscattered wave on the angular distribution of Auger electrons from adsorbed atoms. 相似文献
10.
11.
Angular distributions of auger electron emission: Clean and gas-adsorbed polycrystalline Ni surfaces
The excitation angle (β) and emission angle (θ) dependences of the Ni M2,3VV (61 eV) and Ni L3VV (850 eV) Auger emissions from clean polycrystalline Ni surfaces, and the S L2, 3 M2, 3M2, 3 (150 eV) Auger emission from S-adsorbed poly-Ni surfaces have been investigated. In the case of Ni (61 eV) and S Auger emissions, the β-dependence shows the distribution, while a significant deviation from is observed for Ni (850 eV) Auger emission. The cosθ distribution and the intermediate between isotropic and cosθ distributions are observed for Ni (61 eV), and for Ni (850 eV) and S Auger emissions, respectively. Those results have been found to be in fairly good agreement with the calculations based on the simple continuum model without consideration of the diffraction effect and the inherent anisotropic emission. 相似文献
12.
Auger electron spectra of clean Mg and Fe surfaces have been investigated under UHV conditions. The main Auger peaks in the low energy Auger spectra of these elements are identified as due to L2,3VV and M2,3VV transitions for Mg and Fe respectively. Changes in the low energy spectra of these clean surfaces of Mg and Fe due to chemisorption of residual oxygen in the UHV system, were also studied. The results indicate that for each oxidised surface new larger Auger peaks appear at energies lower than the original main peaks in the clean spectra. The changes in the spectra are believed to be due to the energy shifts of inner energy levels and valence bands involved in the Auger transitions as an oxide is formed. 相似文献
13.
《Solid State Communications》1987,64(2):189-192
The electron energy loss spectra associated with N23-excitation and the low energy N23VV Auger emission have been studied for both the clean and oxygen exposed zirconium. In the high energy side of the N23VV Auger spectrum, autoionization emission of electrons of the valence band due to the decay of 4p electrons excited to states ≈9eV above the Fermi level has been identified. The excitation process can be also observed in the electron energy loss spectra. This is the first time that an autoionization feature is observed in a electron excited Auger spectrum of a 4d transition metal. 相似文献
14.
The integrated areas of the Al L23VV and O KL23L23 Auger peaks and the Al surface plasmon energy ?ωS are reported for the Al(001) surface as a function of exposure to O in the exposure range 0–114 L(1 L=1langmuir=10?6Torr sec). It is shown that for exposures below a critical value of 15 L, ?ωS is constant within experimental error while the O Auger peak area increases linearly. For exposures above 15 L, ?ωS decreases linearly from 10.5 eV to 8.5 eV and the O Auger peak area undergoes relatively slow linear increases correspondingly. The Al Auger peak area decreases by 30% per 1 eV decrease of ?ωS. The results are discussed with reference to theory relating Auger transition intensities to the spectral density function. 相似文献
15.
The energy distributions N(E) of secondary electrons emitted from GaP and InP samples bombarded with 40 keV Ar+ ions have been studied by a retarding potential method and an electronic derivation. The spectra show beyond an intensive peak developed at 2 eV, a detailed spectrum between 80 and 140 eV. The analysis of this spectrum reveales Auger electrons corresponding to L23(P) VV and L23MIV–V(Ga) V [or L23(P) NIV-V(In) V] transitions; moreover, peaks due to plasmon excitations and d band excitations can be distinguished. 相似文献
16.
The fine structure of the M45N45N45 Palladium Auger transition was investigated. The energy of the peaks and the changes of their shapes due to surface modifications, either by alloying or by oxidation are studied. It is found that the fine structure is due to the overlapping of two “band-like” transitions of the type M4VV and M5VV. 相似文献
17.
Angle-resolved sulphur L2.3VV Auger electron spectra have been taken from sulphur adsorbed on Ni {111} at a range of coverages both below and above those corresponding to the ordered (2 × 2) structure. These data indicate that the local adsorption site in the low coverage lattice gas is the same single three-fold hollow site adopted in the ordered overlayer. This contrasts with the low coverage occupation of both three-fold hollow sites for the system I/Ag<{111}. 相似文献
18.
《Journal of Electron Spectroscopy and Related Phenomena》2002,122(3):275-284
Supercell method is used to study the relaxation and screening effects on the initial state of the Auger transition in metals. Our consideration is based on the assumption that when a core-hole exists long enough before the Auger transition occurs, the occupied valence states relax to screen the core-hole which results in a redistribution of the valence electrons, in particular within the atom that contains the core-hole. In order to make the interaction between the core-holes sites at different atoms negligible, the real metal is simulated by supercells repeated periodically. In each supercell one atom is considered to have a core-hole and many others not to have one. The electronic states concerned by the Auger transition are calculated by the self-consistent full-potential linearized augmented plane wave (FLAPW) method. Different responses of the local valence band on the site of the core-hole have been shown depending on whether the d-bands are partially or completely filled. According to the final state rule, the screening to the two holes in the local valence band after the Auger transition has also been considered, as examples, for Ni and Cu metals. The result shows that, with the existence of two holes in them, the states of the local valence band of Cu relax to atomic-like impurity states, while the local valence band of Ni changes to a much narrow band at the bottom of the original band. As examples, L3VV and M1VV Auger spectral profiles of Cu have been calculated in reasonably good agreement with the experiment. 相似文献
19.
The influence of the anisotropy of backscattering of electrons with energies above the core hole ionization energy of selected Auger processes on the anisotropy of the Auger electron emission is studied using a cylindrical W single crystal. After the determination of the anisotropy of the elastic backscattering its contribution to the anisotropy of Auger electron emission from adsorption layers is obtained by postulating that all other anisotropy causes are negligible. When applied to an adsorbate with orientation-independent coverage such as Fe this leads to an orientation-dependent backscattering correction term which may be applied to adsorbates with orientation-dependent sticking coefficients such as O2. In this manner Auger signals may be converted into true relative coverages (corrected for backscattering anisotropy). In the case of oxygen adsorption this correction is significant and leads to an orientation-independent initial sticking coefficient (of 1) over most of the 〈110〉 zone except in the neighbourhood of the {110} planes where it reaches its minimum value of 0.28. 相似文献
20.
The adsorption of hydrogen on a clean Cu10%/Ni90% (110) alloy single crystal was studied using flash desorption spectroscopy (FDS), Auger electron spectroscopy (AES), and work function measurements. Surface compositions were varied from 100% Ni to 35% Ni. The hydrogen chemisorption on a-surface of 100% nickel revealed strong attractive interactions between the hydrogen atoms in accordance with previous work on Ni(100). Three desorption states (β1, β2 and α) appeared in the desorption spectra. The highest temperature (α) state was occupied only after the initial population of the β2-state. As the amount of copper was increased in the nickel substrate, desorption from the higher energy binding α-state was reduced, indicating a decrease in the attractive interactions among hydrogen atoms. The hydrogen coverage at saturation was not affected by the addition of copper to the nickel substrate until the copper concentration was greater than 25% at which a sharp reduction in saturation coverage occurred. This phenomenon was apparently due to the adsorption of hydrogen on Ni atoms followed by occupation of NiNi and CuNi bridged adsorption sites, while occupation of CuCu sites was restricted due to an energy barrier to migration. 相似文献