Characteristic electron energy loss structure for clean and oxidized chromium surfaces

AES and EELS spectra have been measured on clean and oxidized chromium surfaces. Auger peaks at 31.0 and 44.0 eV of the oxide are attributed to cross transitions between chromium and oxygen: {M_2,3(Cr)V(Cr)V(O)} and {M₁(Cr)L₁(O)V(Cr)} respectively. Core loss features are consistent with valence band structure with a newly observed loss peak at 41.1 eV for the oxidized surface being ascribed to a core exciton with binding energy E_b = 1.6 eV.     

Décomposition thermique du monoxide de carbone sur une surface de molybdène: Formation de couches superficielles de carbone et de carbure

We have investigated the decomposition of carbon monoxide on polycrystalline and (001), (110) monocrystalline molybdenum surfaces. This study was performed by massspectrometry, for thermal desorption studies, Auger electron spectrometry (AES), low energy electron diffraction (LEED) and photoelectron spectroscopy (ESCA). By heating the clean Mo surface in CO or by heating the Mo surface covered with CO, the dissociation of chemisorbed CO leads to a build-up of carbon layer which inhibits the subsequent adsorption. Two distinct types of fine structure are associated with the KLL line of carbon Auger spectra. If the Mo surface is heated at a temperature between 300 and 1500 K, the Auger peak is characteristic of a “graphite layer”. If the Mo surface is heated at a temperature up to 2000 K, the Auger peak is characteristic of a “carbure” layer. This “carbure layer” give rise to a surstructure which agrees with a Mo₂C surface layer and was also investigated by ESCA. Chemical shifts of (1s) C and (3d) Mo photoemission bands were observed and attributed to the bounding between Mo and C atoms in the Mo₂C layer.     

Auger and electron energy loss spectroscopic study of surfaces of iron-sulfur alloy,Fe7S8 and FeS2 cleaved in ultra high vacuum

The surfaces of an iron-210 at. ppm sulfur alloy, Fe₇S₈ and FeS₂ cleaved in an ultra high vacuum were studied by Auger (AES) and electron energy loss Spectroscopy (EELS). The S LVV Auger transition for the intergranular fracture plane of the alloy indicates that the sulfur is bonded to the surface as though it were adsorbed. The loss energies of the transition from valence to conduction bands for the surface are identical to those for the transgranular fracture planes. The trans- and intergranular fracture planes have very similar fine structure in the Fe MVV Auger transition profile. This indicates that the interaction between iron and sulfur is too weak to perturb the electronic structure at the fracture surface. The spectral features of the electron transitions having kinetic energies between approximately 40 and 50 eV are explained by a normal Fe MVV Auger transition and an autoionization process after excitation of Fe 3p electrons. The low spin ferrous ion in FeS₂ results in triplet peaks for the Fe MVV transition and doublet peaks for the autoionization event, but similar transitions for Fe₇S₈ exhibit singlet peak for each process.     

钼的晶界内耗峰及少量间隙杂质影响晶界脆性的机制

用扭摆法测出钼的晶界内耗峯,频率约为1周/秒,峯温在1020℃附近,渗氧或渗碳可使晶界峯消失,但在较低温度出现合金晶界峯:氧峯在890℃附近;碳峯在925℃附近。由于钼单晶的内耗曲线上没有出现这些峯,故可认为都是晶界弛豫引起,如果试样中同时有氧和碳,又在960℃和985℃附近出现两个合金晶界峯,用改变频率方法求得各峯激活能,其相对大小与各峯的峯温次序相同,即氧晶界峯的激活能最小(80千卡/克分子);碳晶界峯次之(98千卡/克分子);纯钼晶界峯最大(119千卡/克分子);其他两个峯激活能略小于纯钼晶界峯。配合了断口金相试验,观察到当有氧峯出现时断口晶界面上有黑色氧化物沉淀粒子;当有碳峯出现时,晶界面上有羽毛状碳化物;当试样中同时有氧和碳存在时,也即当内耗曲线上出现960℃和985℃交互作用峯时,晶界面上有大量的有黑圈的白色沉淀物。从以上结果我们对少量间隙杂质在钼的晶界脆性中所起作用,特别是氧和碳同时存在时能起改善脆性的作用提出了一种看法。     

Surface electronic structure of α-Mo2C(0 0 0 1)

The electronic structure of α-Mo₂C(0 0 0 1) has been investigated by angle-resolved photoemission spectroscopy utilizing synchrotron radiation. A sharp peak is observed at 3.3 eV in normal-emission spectra. Since the peak shows no dispersion as a function of photon energy and is sensitively attenuated by oxygen adsorption, the initial state of the peak is attributed to a surface state. Resonant photoemission study shows that the state includes substantial contribution of 4d orbitals of the Mo atoms in the second layer. The emissions with constant kinetic energies of 22 and 31 eV above the Fermi level (E_F) are found in normal-emission spectra, and these emissions are interpreted as originating from the Mo N₁N₂₃V and N₂₃VV Auger transitions, respectively.     

Electron energy loss spectroscopy study of the initial stage of lanthanum oxidation

The electron energy loss spectra (EELS) of a pure metallic lanthanum surface and variations in these spectra at the initial stages of surface oxidation were studied. The measurements were performed at primary-electron beam energies E _p from 200 to 1000 eV. A very pronounced peak at a loss energy of about 7.5 eV arises due to transitions from the La4d electronic states of the valence band into the empty La4f electronic states of the conduction band at 5.0–5.5 eV above the Fermi level. Marked changes are observed in the EELS during the oxidation of lanthanum: the peak at an energy of 7.5 eV disappears, and the peak at 13.5 eV corresponding to bulk collective energy loss in lanthanum oxide becomes more pronounced. The results obtained are discussed in terms of the electronic structure of lanthanum and lanthanum oxide.     

Electron-stimulated desorption of potassium and cesium atoms from oxidized molybdenum surfaces

The electron-stimulated desorption (ESD) yields and energy distributions for potassium (K) and cesium (Cs) atoms have been measured from K and Cs layers adsorbed at 300 K on oxidized molybdenum surfaces with various degrees of oxidation. The measurements were carried out using a time-of-flight method and surface ionization detector. The ESD appearance threshold for K and Cs atoms is independent of the molybdenum oxidation state and is close to the oxygen 2s level ionization energy of 25 eV. Additional thresholds for both K and Cs atoms are observed at about 40 and 70 eV in ESD from layers adsorbed on an oxygen monolayer-covered molybdenum surface; they are associated with resonance processes involving Mo 4p and 4s excitations. The ESD energy distributions for K and Cs atoms consist of single peaks. The most probable kinetic energy of atoms decreases in going from cesium to potassium and with increasing adsorbed metal concentration; it lies in the energy range around 0.35 eV. The K and Cs atom ESD energy distributions from adlayers on an oxygen monolayer-covered molybdenum surface are extended toward very low kinetic energies. The data can be interpreted by means of the Auger stimulated desorption model, in which neutralization of adsorbed alkali-metal ions occurs after filling of holes created by incident electrons in the O 2s, Mo 4s or Mo 4p levels.     

EELS characterization of TiN grown by the DC sputtering technique

Titanium nitride thin films were deposited on monocrystalline silicon (mc-Si) substrates by direct current reactive magnetron sputtering. Auger electron spectra (AES) of deposited films at different nitrogen partial pressures, show the typical N KL₂₃L₂₃ and Ti L₃M₂₃M₂₃ Auger transition overlapping. Also, changes in the Ti L₃M₂₃M₄₅ Auger transition peak are observed. X-ray diffraction and high resolution electron microscopy (HRTEM) of a golden color TiN/mc-Si sample, reveal a preferential polycrystalline columnar growth in the 〈111〉 orientation. This sample was also analyzed by electron energy-loss spectroscopy (EELS). The N/Ti elemental ratio is slightly different to the value determined by AES. Atomic distribution around the N atoms is in agreement with that expected from the N atom in the fcc unit cell of TiN. This distribution was obtained via an extended energy-loss fine structure (EXELFS) analysis from EELS spectra.     

氧含量对CaCu3Ti4O12巨介电常数和介电过程的影响

本文研究了在真空、空气和氧气中烧结制备的三种 CaCu₃Ti₄O₁₂陶瓷材料的介电特性. 交流阻抗测量结果表明在10—300 K温度范围, 三种样品的介电温谱中均出现三个平台, 其电阻实部和电容虚部在相应温度出现损耗峰, 真空条件烧结的样品具有较高的介电平台和较明显的电阻实部与电容虚部峰值, 表明氧含量和氧空位对CaCu₃Ti₄O₁₂的介电性质具有重要影响, 介电温谱出现的三个平台分别源于晶粒、晶界及氧空位陷阱.温谱分析表明晶粒的激活能与烧结气氛有较大关系,氧空位引起的电子短程跳跃及跳跃产生的极化子是晶粒电导和电容的主要起源.氧空位陷阱的激活能基本与烧结气氛无关,约为0.46 eV. 氧空位对载流子的陷阱作用是CaCu₃Ti₄O₁₂ 低频高介电常数的重要起源.     

Electron-stimulated desorption of potassium and cesium atoms from an oxidized molybdenum surface

The yield and energy distributions of potassium and cesium atoms emitted in electron-stimulated desorption (ESD) from a molybdenum surface, oxidized to different extent and maintained at 300 K, have been measured by the time-of-flight technique with a surface ionization detector. The ESD threshold for potassium and cesium atoms lies around 25 eV, irrespective of molybdenum oxidation state. In the case of molybdenum coated by an oxygen monolayer, secondary thresholds at ∼40 and ∼70 eV have been observed, as well as atomic energy distribution tailing down to very low energies. The most probable kinetic energies of the atoms are a few tenths of one eV. The results are explained within a model involving Auger neutralization of the adsorbed alkali metal ions after the filling of the 2s O, 4s Mo, and 4p Mo core holes. The possibility of ESD of a neutral species as a result of oxide-cation core-level ionization has been demonstrated for the first time. Fiz. Tverd. Tela (St. Petersburg) 39, 758–761 (April 1997)     

Segregation of sulphur on a molybdenum surface studied by auger electron spectroscopy

The kinetic behaviour of sulphur segregation was studied during heat treatment of a molybdenum ribbon between 750°C and 1350°C by using an Auger electron spectroscopic technique. When the specimen is heated to high temperatures, the sulphur present as an impurity in the polycrystalline molybdenum diffuses on to the surface along grain boundaries. The intensity changes of Auger electron signals of sulphur and molybdenum showed that the rate of the diffusion remained constant until the surface was covered with a first sulphide layer in the temperature range studied. The activation energy in the initial stage of the diffusion was 26kcal/mol. High resolution Auger spectra of the sulphur were measured and explained from the density of states of MoS₂.     

Electron-stimulated desorption of sodium atoms from oxidized molybdenum

The time-of-flight technique combined with a surface-ionization-based detector has been used to investigate the yield and energy distribution of sodium atoms escaping in electron-stimulated desorption (ESD) from adlayers on the surface of molybdenum oxidized to various degrees and maintained at T=300 K as functions of incident electron energy and surface coverage by sodium. The sodium-atom ESD threshold is about 25 eV, irrespective of sodium coverage and extent of molybdenum oxidation. Molybdenum covered by an oxygen monolayer exhibits secondary thresholds at ∼40 eV and ∼70 eV, as well as low-energy tailing of the energy distributions, its extent increasing with surface coverage by sodium Θ. The most probable kinetic energies of sodium atoms are about 0.23 eV, irrespective of the degree of molybdenum oxidation and incident electron energy at Θ=0.125, and decrease to 0.17 eV as the coverage grows to Θ=0.75. The results obtained are interpreted within a model of Augerstimulated desorption, in which adsorbed sodium ions are neutralized by Auger electrons appearing as the core holes in the 2sO, 4sMo, and 4pMo levels are filled. It has been found that the appearance of secondary thresholds in ESD of neutrals, as well as the extent of their energy distributions, depend on surface coverage by the adsorbate. Fiz. Tverd. Tela (St. Petersburg) 40, 768–772 (April 1998)     

Characterization of doped diamond-like carbon films deposited by hot wire plasma sputtering of graphite

Diamond-like carbon (DLC) films doped with nitrogen and oxygen were deposited on silicon(100) and polytetrafluoroethylene (PTFE) substrates by hot wire plasma sputtering of graphite. The morphology and chemical composition of deposited films has been characterized by scanning electron microscopy, XPS, Auger, FTIR spectroscopy and micro-Raman scattering. Plasmon loss structure accompanying the XPS C 1s peak and electron energy loss spectroscopy (EELS) in reflection mode was used to study the fraction of sp³ bonded C atoms and the density of valence electrons. Raman spectra show two basic C–C bands around 1575 cm^-1 (G line) and 1360 cm^-1 (D line) . Auger depth profiling spectroscopy was used to measure the spatial distributions of C, N and O atoms in the surface layer of DLC films. The fraction of sp³ bonded atoms of about 40% was detected in DLC films by XPS plasmon loss and EELS techniques. Nitrile and iso-nitrile groups observed in FTIR spectra demonstrated the existence of sp bonded carbon in doped DLC films. The typical for DLC films specific density 1.7–1.8 g/cm³ was obtained from EELS and XPS data. PACS 52.77.Dq; 81.65.-b; 82.80.Pv     

Grain boundary chemistry and grain boundary dislocations in bulk YBa2Cu3O7-δ

We report the results of our microchemical analyses of low- large-angle grain boundaries in bulk YBa₂Cu₃O_7- using nanoprobe energy-dispersive-X-ray spectroscopy (EDX) and electron-energy-loss spectroscopy (EELS). We observed periodic variation in the concentration of Cu along the boundaries, and oxygen depletion at the boundaries. We found that the chemistry of the grain boundary is very sensitive to grain boundary dislocations (GBDs), while, in turn, the configuration of the GBDs is very sensitive to the boundary misorientation and the boundary plane normal. The strain field associated with closely spaced GBDs reduced the density of mobile holes at the boundary, which is expected to be detrimental to the superconducting properties of the boundary. The possible structural transition of the grain boundaries from an oxygen-deficient state to a fully oxygenated state near a coincidence orientation is discussed, based on the reduction of the elastic strain energy of the boundaries.     

AES/STEM grain boundary analysis of stabilized zirconia ceramics

Semiquantitative Auger Electron Spectroscopy (AES) on pure monophasic (ZrO₂)_0.83(YO_1.5)_0.17 was used to determine the chemical composition of the grain boundaries. Grain boundary enrichment with Y was observed with an enrichment factor of about 1.5. The difference in activation energy of the ionic conductivity of the grain boundary compared with the bulk can be explained by the Y segregation.When Bi₂O₃ is introduced into this material and second phase appears along the grain boundaries of the cubic main phase. Energy dispersive X-ray analysis (EDS) on a scanning transmission electron microscope (STEM) shows an enrichment of bismuth at the grain boundaries of this second phase.     

碳和氧在钼(110)表面上形成的有序结构

使用LEED和AES研究了钼(110)表面上的碳和氧,用能最为1千电子伏束流为6微安的氩离子轰击含碳和氧的钼(110)表面,发现碳的峰形和强度发生了变化,深度剖面分析指出,碳层是来源于体内,加热样品到700℃和750℃以上分别观察到碳的c(4×4)-碳和-碳两种有序结构. 关键词：     

Changes in Auger spectra of Mg and Fe due to oxidation

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 L_2,3VV and M_2,3VV 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.     

Optical and luminescence properties of CdWO4 and CdWO4:Mo single crystals

Luminescence properties of a pure CdWO₄ crystal and a CdWO₄:Mo crystal doped with molybdenum in different concentrations have been investigated. The effect of molybdenum impurity on the intrinsic luminescence of CdWO₄ has been found, and the role of the impurity in the formation of new luminescence centers has been investigated. The features of the formation of the intrinsic and impurity luminescence excitation spectra of CdWO₄ and CdWO₄:Mo crystals in the fundamental-absorption region have been considered. The reflection spectra of the CdWO₄ crystal have been investigated taking into account the crystal structure anisotropy.     

A study of the adsorption of oxygen on Ni(111) using auger electron spectroscopy: Chemical shifts and valence spectra

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 cm^2? 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 M_{2, 3}VV (61 eV) and L₃M_{2, 3}V (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 L₃M_{2, 3}M_{2, 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.     

The adsorption and reaction of H2O on clean and oxygen covered Ag(110)

The adsorption and reaction of water on clean and oxygen covered Ag(110) surfaces has been studied with high resolution electron energy loss (EELS), temperature programmed desorption (TPD), and X-ray photoelectron (XPS) spectroscopy. Non-dissociative adsorption of water was observed on both surfaces at 100 K. The vibrational spectra of these adsorbates at 100 K compared favorably to infrared absorption spectra of ice Ih. Both surfaces exhibited a desorption state at 170 K representative of multilayer H₂O desorption. Desorption states due to hydrogen-bonded and non-hydrogen-bonded water molecules at 200 and 240 K, respectively, were observed from the surface predosed with oxygen. EEL spectra of the 240 K state showed features at 550 and 840 cm^?1 which were assigned to restricted rotations of the adsorbed molecule. The reaction of adsorbed H₂O with pre-adsorbed oxygen to produce adsorbed hydroxyl groups was observed by EELS in the temperature range 205 to 255 K. The adsorbed hydroxyl groups recombined at 320 K to yield both a TPD water peak at 320 K and adsorbed atomic oxygen. XPS results indicated that water reacted completely with adsorbed oxygen to form OH with no residual atomic oxygen. Solvation between hydrogen-bonded H₂O molecules and hydroxyl groups is proposed to account for the results of this work and earlier work showing complete isotopic exchange between H₂¹⁶O_(a) and ¹⁸O_(a).