Auger electron spectroscopy studies of In4Se3 layered crystals

In₄Se₃ pure and silver intercalated layered semiconductor crystals’ surfaces have been studied with application of Auger electron spectroscopy (AES). It was found that peculiarities of their adsorptial activity appear as the result of atomic and electron-energetic structure of the crystals’ cleavage surfaces. Silver intercalation (2.5–3 at.%) of In₄Se₃ leads to a rise in the CO sticking coefficient and simultaneous appearance of adsorption activity relative to oxygen. It was established that In₄Se₃ crystal heating leads to active interaction of cleavage surfaces with oxygen and its chemisorption.     

The adsorption of methyl iodide on uranium and uranium dioxide: Surface characterization using X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES)

The adsorption of methyl iodide on uranium and on uranium dioxide has been studied at 25 °C. Surfaces of the substrates were characterized before and after adsorption by X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). The XPS binding energy results indicate that CH₃I adsorption on uranium yields a carbide-type carbon, UC, and uranium iodide, UI₃. On uranium dioxide the carbon electron binding energy measurements are consistent with the formation of a hydrocarbon, —CH₃-type moiety. The interpretation of XPS and AES spectral features for CH₃I adsorption on uranium suggest that a complex dissociative adsorption reaction takes place. Adsorption of CH₃I on UO₂ occurs via a dissociative process. Saturation coverage occurs on uranium at approximately two langmuir (1 L = 10^?6 Torr s) exposure whereas saturation coverage on uranium dioxide is found at about five langmuir.     

Structure and surface layers of Mg-C nanocomposites produced by ball milling

X-ray diffractometry (XRD), X-ray photoelectron spectrometry (XPS), Auger electron spectrometry (AES) and transmission electron microscopy (TEM) were used to investigate the structure and surface layers properties of nanocomposites produced by the mechanical activation (ball milling) of elemental magnesium with carbon materials (amorphous carbon and graphite). Amorphous carbon was synthesized by electric discharge treatment in kerosene. It was shown that ball milling, the allotropic form of carbon materials, and features of hydrogenation have a considerable effect on the structure, surface layer properties, and hydrogen adsorption of a formed composition. XPS and Auger spectroscopy revealed the surface layer of the composite particles to be enriched with carbon. In addition, there were oxide layers on their surfaces due to the particles’ interaction with the environment.     

The bonding state of carbon segregated to α-iron surfaces and on iron carbide surfaces studied by electron spectroscopy

Segregated carbon on the Fe(100) surface has been studied by means of X-rayand ultraviolet photoelectron (XPS, UPS), Auger electron (AES) and electron energy loss spectroscopy (ELS). For comparison, the surfaces of polycrystalline graphite and of iron carbides stabilized by chromium or manganese additions have been investigated. On the iron surface, carbon exists as a chemisorbed state or graphitic multilayer. The two states exhibit different energy positions in XPS, and are different in energy positions and lineshapes in AES and ELS. During the transition of graphitic carbon to chemisorbed carbon on Fe(100) a novel coverage-dependent Auger feature is reported. The spectra of graphitic carbon on the iron surface always coincide with those of solid graphite. The carbon Auger transitions of chemisorbed carbon and of iron carbides exhibit very similar lineshapes, but the energy positions of both states differ in AES as well as XPS.     

P2S5/NH4OH处理GaAs(100)表面的电子能谱研究

采用俄歇电子能谱(AES)和X射线光电子能谱(XPS)研究了P₂S₅/NH₄OH钝化液处理的GaAs(100)表面的微观特性。AES测量表明,在钝化膜和GaAs衬底之间的界面处无O组分,只有P和S组分。XPS测量分析指出,经过P₂S₅/NH₄OH溶液处理后,GaAs表面处Ga₂O₃和As₂O_{3关键词：}     

Investigation of ageing characteristics and identification of surface chemical changes on SrGa2S4:Ce display phosphor under electron beam bombardment

Cathodoluminescent ageing characteristics of SrGa₂S₄:Ce³⁺ under prolonged electron beam bombardment was studied and the data are presented. The cathodoluminescent intensity with an increasing Coulomb loading was observed to degrade under different primary electron beam voltages. Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) were used to monitor the surface chemical changes during electron beam bombardment and after the degradation process. Auger peak to peak heights monitored during the ageing process suggest a loss in S and C and an initial increase in oxygen concentration on the surface. XPS results indicate the formation of a SrO overlayer due to electron stimulated surface chemical reactions (ESSCRs).     

Ta/Ni/Ta multilayered ohmic contacts on n-type SiC

The interface formation, electrical properties and the surface morphology of multilayered Ta/Ni/Ta/SiC contacts were reported in this study. It was found that the conducting behavior of the contacts so fabricated is much dependent on the metal layer thickness and the subsequent annealing temperature. Auger electron spectroscopy (AES) and X-ray diffraction analyses revealed that Ni₂Si and TaC formed as a result of the annealing. The Ni atoms diffused downward to metal/SiC interface and converted into Ni₂Si layer in adjacent to the SiC substrate. The released carbon atoms reacted with Ta atoms to form TaC layer. Ohmic contacts with specific contact resistivity as low as 3 × 10⁻⁴ Ω cm² have been achieved after thermal annealing. The formation of carbon vacancies at the Ni₂Si/SiC interface, probably created by dissociation of SiC and formation of TaC during thermal annealing, should be responsible for the ohmic formation of the annealed Ta/Ni/Ta contacts. The addition of Ta into the Ni metallization scheme to n-SiC restricted the accumulation of carbon atoms left behind during Ni₂Si formation, improving the electrical and microstructure properties.     

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.     

Spectroscopic analysis of CIGS2/CdS thin film solar cell heterojunctions on stainless steel foil

This paper presents a spectroscopic analysis of the interface between a CuIn_1−xGa_xS₂ (CIGS2) absorber and a CdS buffer layer on stainless steel foil by Auger electron spectroscopy (AES), inverse photoemission spectroscopy (IPES) and photoelectron spectroscopy (PES) such as X-ray photoelectron spectroscopy (XPS), and ultraviolet photoelectron spectroscopy (UPS). By combining these spectroscopic techniques, detailed information about the electronic and chemical properties of the CIGS2 surface and the CdS/CIGS2 interface can be obtained. The gallium concentration in CIGS2 films was found to increase continuously towards the Mo back contact. XPS analysis showed the presence of KCO₃ on the surface of CdS, deposited on etched and un-oxidized samples indicating diffusion of potassium. No potassium was observed on oxidized as well as samples having thicker CdS (50 nm) indicating the effectiveness of oxidation and chemical bath deposition (CBD) process in cleaning the sample surface effectively. In addition, investigation of the electronic level alignment at the interface has been carried out by combining PES and IPES. Conduction band offset of −0.45 (±0.15) eV and a valence band offset of −1.06 (±0.15) eV were measured. These unfavorable conditions limit efficiency of CIGS2 thin film solar cells.     

Degradation of Y2SiO5:Ce phosphor powders

The degradation of the cathodoluminescence (CL) intensity of cerium-doped yttrium silicate (Y₂SiO₅:Ce) phosphor powders was investigated for possible application in low voltage field emission displays (FEDs). Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS) and CL spectroscopy were used to monitor changes in the surface chemical composition and luminous efficiency of commercially available Y₂SiO₅:Ce phosphor powders. The degradation of the CL intensity for the powders is consistent with a well-known electron-stimulated surface chemical reaction (ESSCR) model. It was shown with XPS and CL that the electron stimulated reaction led to the formation of a luminescent silicon dioxide (SiO₂) layer on the surface of the Y₂SiO₅:Ce phosphor powder. XPS also indicated that the Ce concentration in the surface layer increased during the degradation process and the formation of CeO₂ and CeH₃ were also part of the degradation process. The CL intensity first decreased until about 300 C cm⁻² and then increased due to an extra peak arising at a wavelength of 650 nm.     

Surface analysis and oxidation behavior of Y-ion implanted AZ31 magnesium alloys

AZ31 samples were implanted with yttrium ions with fluences of 5 × 10¹⁶, 1 × 10¹⁷ and 5 × 10¹⁷ ions/cm², using a metal vapor vacuum arc source at an extraction voltage of 45 kV. The surfaces of the implanted samples were then analyzed by Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS). It was found that after treatment a pre-oxidation layer was formed, and the higher the fluence, the thicker the pre-oxidation layer was. The valence states showed that yttrium existed in the form of Y₂O₃. Isothermal oxidation tests have been conducted in pure oxygen at 773 K for 90 min to evaluate the oxidation behavior of the implanted samples. The results indicate that after implantation the oxidation resistance of the samples was significantly improved. Moreover, the greater the fluence, the better the oxidation resistance has been achieved. The characterization of the implanted layers after isothermal oxidation was examined by SEM, AES and XPS. From the results, it can be found that the thickness of the oxide scale formed on the implanted surfaces have been greatly decreased, and there is no obvious change for both the thickness of the pre-oxidation layer and the valence states of the elements after oxidation.     

Oxidation of GaN{0001}-11 surfaces at room temperature

The interaction of unexcited oxygen molecules with clean GaN{0001}-11 surfaces was investigated using X-ray photoemission spectroscopy (XPS), Auger electron spectroscopy (AES), and low-energy electron diffraction (LEED). Clean surfaces were prepared by a HF dip followed either by desorption of Ga films deposited at room temperature or by nitrogen-ion bombardment and annealing. During exposures in the range from 0.3 up to 10¹⁵ L-O₂ any excitations of the oxygen were avoided. Oxygen coverages determined from the XPS and the AES data differ by a factor of two. The larger XPS-derived coverages are considered to be more reliable since the AES signals decayed during data recording. The oxygen uptake takes place in two consecutive stages. The first one is identified as dissociative chemisorption and the second one is tentatively attributed to field-assisted diffusion by the Mott-Cabrera mechanism. The dissociative chemisorption is characterized by an initial sticking coefficient of and a saturation coverage of monolayers that is reached after exposures of 10³ L-O₂. The second mechanism sets in at exposures to 10⁸ L-O₂ but reaches no saturation even with the largest doses applied. Received 4 September 1998 and Received in final form 6 November 1998     

Auger parameters of ternary Pd–Ni–P amorphous alloys

A series of bulk ternary amorphous alloys of Pd_{100?3 x} Ni_{2 x} P _x were prepared and their amorphicity checked by X-ray diffraction (XRD) and neutron scattering. Auger parameters of these alloys have been derived from X-ray photoelectron spectroscopy (XPS) and X-ray excited Auger electron spectra (AES). Experiments of XPS and AES on each elemental metal and Ni₂P were also performed for comparison. The results show a clear compositional dependence for the 3d binding energies and the MNN Auger energies of Pd on alloying, while Ni 2p core levels and the Ni LMM Auger lines show a weaker variation. Analysis of the data using “excited atom” models indicates electron transfer from Pd, with P carrying negative charge, but the differences in behaviour of the two metallic species suggests that covalent bonding changes may be significant.     

The interaction of H2S with Si(111) 7 × 7 surfaces by energy loss and Auger electron spectroscopies

Low energy electron loss spectroscopy (ELS) and Auger electron spectroscopy (AES) have been applied for the studies of the interaction of H₂S molecules with Si(111)7 × 7 surfaces. The observations are consistent with the interpretation that the room temperature non-dissociative adsorption state of H₂S molecules changes substantially after annealing at 550°C, resulting in the desorption of hydrogen and the covalent bond formation between silicon and sulfur atoms. The silicon disulfide films formed on Si(111) surfaces have been identified by the characteristic loss peaks in comparison with those of silicon dioxide.     

Auger electron spectroscopic study of CO2 adsorption on Zircaloy-4 surfaces

We investigate the adsorption of CO₂ onto Zircaloy-4 (Zry-4) surfaces at 150, 300 and 600 K using Auger electron spectroscopy (AES). Following CO₂ adsorption at 150 K the graphitic form of carbon is detected, whereas upon chemisorption at 300 and 600 K we detect the carbidic phase. As the adsorption temperature is increased, the carbon Auger signal increases, whereas the oxygen signal decreases. Adsorption at all three temperatures results in a shift of the Zr Auger features, indicating surface oxidation. The effect of adsorbed CO₂ on the Zr(MVV) and Zr(MNV) transitions depends on adsorption temperature and is less pronounced at higher temperatures. On the other hand, changes in the Zr(MNN) feature are similar for all three adsorption temperatures. The changes in the Zr Auger peak shapes and positions are attributed to oxygen from dissociated CO₂, with the differences observed at various temperatures indicative of the diffusion of oxygen into the subsurface region.     

Initial oxidation of the Mg(0001) surface,an electron spectroscopy study

The initial oxidation of Mg(0001) has been studied using AES (Auger electron spectroscopy), LEED (low energy electron diffraction), and EELS (electron energy loss spectroscopy). The oxidation proceeds through different stages; first oxygen atoms are incorporated to chemisorption sites below the top layer magnesium. This chemisorption phase is followed by the formation of an oxide layer. The oxide layer covers the Mg surface after an oxygen exposure of ～ 10 L O₂. After this exposure the bulk-like MgO formation slowly increases the oxide thickness. The oxide layer formed for exposures up to ≤ 10 L O₂ gives rise to a diffuse LEED pattern of the same symmetry as the original “clean” LEED pattern; the possibility of an epitaxial oxide formation at this stage is discussed.     

Chemical bond formation during laser bonding of Teflon FEP and titanium

Teflon^® FEP (fluorinated ethylene propylene) is resistant to most chemical solvents, is heat sealable and has low moisture uptake, which make this polymer attractive as a packaging materials for electronics and implantable devices. Teflon^® FEP/Ti microjoints were fabricated by using focused infrared laser irradiation. Teflon^® FEP/Ti interfaces were studied by using X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES) and scanning electron microscopy coupled with energy dispersive spectroscopy (SEM-EDS). The XPS results give evidence for the formation of Ti-F bonds in the interfacial region. The AES and SEM-EDS results show that the chemical bond formation occurs only in the actual bond area. No evidence for chemical bond formation was found in the heat affected zone surrounding the laser bonds.     

Modification of the electronic properties of the TiO2 (1 1 0) surface upon deposition of the ultrathin conjugated organic layers

A few nm thick 3,4,9,10-perylenetetracarboxylic acid dianhydride (PTCDA) and Cu-phthalocyanine (CuPc) overlayers were thermally deposited in situ in UHV onto TiO₂ (1 1 0) surface. Atomic composition of the surfaces under study was monitored using Auger electron spectroscopy (AES). The formation of the interfacial potential barrier and the structure of the unoccupied electronic states located 5-25 eV above the Fermi level (E_F) was monitored using a probing beam of low-energy electrons according to the total current electron spectroscopy (TCS) method. The work function values upon the overlayer deposition changed from 4.6 to 4.9 eV at the PTCDA/TiO₂ (1 1 0) interface and from 4.6 to 4.3 eV at the CuPc/TiO₂ (1 1 0) interface. Band bending in the TiO₂ substrate, molecular polarization in the organic film and changes in the work function due to the change in the surface composition were found to contribute to the formation of the interfacial potential barriers. Oxygen admixture related peaks were observed in the AES and in the TCS spectra of the CuPc overlayers. A mechanism of the transformations in the PTCDA and CuPc overlayers on the TiO₂ (1 1 0) upon elevating temperature from 25 to 400 °C was suggested.     

Analysis profiles of oxide films on chrome steel by auger emission and x-ray photoelectron spectroscopies

Samples of steel from two different sources were examined. The materials had nominally the same bulk composition but different samples from each batch had been hardened under two slightly different conditions.The surface oxide films were analysed by both Auger emission spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) after a number of ion bombardments, and the variation in composition with depth was established. In general the outermost oxide layers were chromium deficient and XPS results suggested the presence of Fe₂O₃ at the surface, together with atmospheric contamination. After ion bombardment the proportion of chromium oxide increased and both iron metal and oxide (Fe₃O₄) were present. The amount of chromium oxide reached a maximum at the steel oxide interface and on further bombardment was replaced by chromium metal. AES and XPS results were in agreement qualitatively and also quantitatively after measurement with a curve analyser of the areas under the peaks of certain elements.The present investigation has shown that AES and XPS can give very similar analyses provided some simple corrections are applied. However, the use of the higher resolution of XPS can provide additional information which cannot be obtained by AES. Thus, using expanded XPS scans, together with suitable curve analysis techniques, it is relatively simple to separate signals from oxide and from free metal regions of the sample, and to study in detail the changes in composition of the oxide from the oxide-air to the oxide-metal interfaces.The study of the four steel samples in this manner has shown that there is a thin region rich in chromium oxide adjacent to the metal. The high level of chromium falls off fairly rapidly nearer the surface and appears to stabilize at a very low level. This is particularly obvious in the thicker oxides (PH), where there is a thick surface layer which is principally iron oxide. It would appear that under the conditions of the heat treatment given to the present samples the thickening of the oxide is due almost entirely to iron oxide. Other work has shown that the low temperature air-formed oxide on these steels is chromium rich and it is suggested that the thickening is due to diffusion of iron through the original film with little movement of the chromium.In view of the high chromium deficiency in the outer layers of the oxides examined it is apparent that the supposedly protective chromium oxide film on chrome steel is situated at the oxide-metal interface and not on the outer surface.The present investigation has shown the existence of two unreported iron satellites. One would appear to be associated with the mixed valence oxide Fe₃O₄ and another with the purely trivalent oxide Fe₂O₃. The satellites could be associated with a strong plasma loss mechanism, or be due to shake-up phenomena as in the case of copper and nickel oxides¹⁴As might be expected from the normal oxidation behaviour of iron, the present oxide films appear to consist of a thin layer of Fe₂O₃ overlying the main Fe₃O₄ oxide. The removal of this outermost Fe₂O₃ layer is rapid and is accompanied by the changes in the satellites mentioned above, together with changes in the position of the Fe 2p_{$\text{3}\text{2}$} oxide peak.In conclusion, it is clear that a detailed XPS examination can not only provide information on overall compositional changes, as can be obtained by AES, but can also provide a comprehensive picture of changes in oxide composition, including those due to oxides of one metal in different valency states.