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Photoemission spectroscopy and X-ray emission spectroscopy have been used to investigate the role of the chemical environment on the electronic structure of SnS, SnS2, Sn2S3 and Li0.57SnS2 compounds. For this purpose, we have studied the Sn 3d5/2 and S 2p1/2,3/2 inner levels and the valence band by photoemission spectroscopy and the S 3p electronic distributions by X-ray emission spectroscopy. We have established fingerprints of the SnII and SnIV valencies in the compounds SnS and SnS2 and have shown that these are observed in Sn2S3 where it is known that both II and IV valencies are present. By comparing the data for Li0.57SnS2 with those for the other compounds, we have demonstrated that the SnII and SnIV signatures are also found in this compound. We have thus ascertained experimentally that Sn is partially reduced in SnS2 upon Li intercalation. In addition, the data have been found to be in excellent agreement with recent densities of electronic states calculations performed in the framework ...

We report a study using X-ray Photoemission Spectroscopy (XPS) of a nanocomposite which is a mixture of silicon nitride (Si3N4) micrometric grains (mean diameter of 0.2 μm) and silicon carbide (SiC) nanoparticles (from 0.01 μm to 0.06 μm). A differential charge effect was detected in this compound for the C1s and Si2p core levels. We concluded that the existence of such an effect was because the first raw acquired spectra display selective partial reductions of the charge for 6–7 h. Contributions to the XPS core levels from silicon carbide (Si–C4 and C–Si4) are not affected by charge shifts, in contrast to other contributions. This differential charge effect was not observed for SiCN nanopowders which display a rigid charge shift of all the contributions in the same core levels. This is a good fingerprint for the structural organization in the compound. We concluded the existence of SiC nanoparticles dispersed in a vitreous YSiAlON[C] phase located at the grain boundaries in the material which made up a conducting cement/skeleton surrounding large silicon nitride grains (0.2 μm).

Chemical bonding in SiCNAlY(O) nanometric powders was investigated by x-ray photoemission spectroscopy. The powders were prepared by laser pyrolysis of binary mixtures of liquid hexamethyldisilazane and disolved solid isopropoxydes. As-prepared powders are amorphous and the atomic proportion of aluminum and yttrium do not exceed 1 at. %. They were annealed at 1600 °C under N2 atmosphere and we followed the evolution of the bonding configuration with annealing treatment for the composition with a C/N atomic ratio equal to 0.78. Two other compositions were studied (powders annealed at 1600 °C): a carbon rich powder (C/N=5.05) and a nitrogen rich powder (C/N=0.09). The strong increase of Al 2p and Y 3d peak intensities relatively to Si 2p peak intensity with annealing underlines an increase of the Al and Y content in superficial layers after annealing. The analysis of the chemical shift of Al 2p core level after annealing underline the appearance of Al–N bonds at 1600 °C. The chemical environment of Y atoms ...

The electronic structure of ultrafine laser synthesized powders with controlled composition have been investigated by using x-ray photoelectron spectroscopy. The Si 2p, C 1s, and N 1s core levels as well as the valence band distributions have been analyzed. The experimental analysis is focused on intermediate composition samples with C/N equal to 0.58 and 0.67; in this range the C/N value remains approximately the same under heat treatments. In as-formed samples, the nanopowders exhibit a high degree of chemical disorder; mixed tetrahedra with both C and N atoms around each Si atom are likely to occur. After a 1500 °C treatment, the powders remain amorphous and the presence of N–C and C–C bonds is clearly shown. After a 1600 °C annealing the samples are crystallized; the measured core levels and valence spectra reveal the presence of C–Si and N–Si bonds in Si–C4 and Si–N4 groups. It is noteworthy that in this case the C 2s and N 2s valence band states appear as two well separated peaks in the valence band...

The influence of the presence of Cu in the amount between 1% and 6% in arsenic chalcogenide glasses is examined through a study of the electronic energy levels by means of x-ray photoelectron and x-ray emission spectroscopy, through an investigation of the low-energy tunneling systems by means of phonon echoes at 0.37 K, and through an examination of the photodarkening and the photoinduced dichroism caused by polarized Ar+ laser irradiation. Possible links between the various effects are examined. The Cu atoms become an integral part of the amorphous lattice structure and strongly influence the photodarkening, but they do not have a significant effect on the tunneling systems or the dichroism. It is concluded that the tunneling levels and the dichroism involve only local configurations, while the photodarkening involves larger-scale areas of the lattice.

An investigation by X-ray photoelectron spectroscopy (XPS) of adhesion mechanisms of a-Si:H films on stainless steel substrates after hydrogen (H2), nitrogen (N2) and ammonia (NH3) plasma treatments of the surface is presented. It is shown that adhesion is increased by N2 treatment. This effect is related to chemical bonding states at the interface. The improvement is attributed to the formation of silicon nitride at the interface and to the existence of Fe–Fe metallic bonds which contribute to a hardening of the substrate.

Polymer-like hydrogenated amorphous carbon (a-C:H) films containing increasing concentrations of Si atoms (up to 12 at.%) have been grown using a dual-mode plasma (microwave and radiofrequency) plasma enhanced chemical vapor deposition reactor with low ion energies. X-ray emission and X-ray photoelectron spectroscopies (giving respectively Si 3p states and the total valence band states) have been used to probe the electronic structure. Complementary information on the local bonding have been obtained from the Si 2p and C 1s core levels. These results show that the Si bonding environments are consistent with Si–C4 units. The influence of the tetrahedrally bonded Si atoms on the C atom local environment is basically explained by a topological effect rather than a change in the C hybridization.

The electronic properties of the crystalline phases of the ${\mathrm{Sb}}_{2}{\mathrm{S}}_{3}{\ensuremath{-}\mathrm{T}\mathrm{l}}_{2}\mathrm{S}$ system are investigated both experimentally and theoretically. Experimental data obtained by x-ray photoelectron spectroscopy and ${}^{121}\mathrm{Sb}$ M\"ossbauer spectroscopy are reported and analyzed from tight-binding calculations, which are used here because of the complexity of the materials. The main features of the x-ray photoelectron valence bands and S $K\ensuremath{\beta}$ emission spectra are identified. The binding energy of the S ${2p}_{3/2}$ core level is found to decrease from ${\mathrm{Sb}}_{2}{\mathrm{S}}_{3}$ to ${\mathrm{Tl}}_{2}\mathrm{S}$ in agreement with the variations of the calculated S charges. We show that the ${}^{121}\mathrm{Sb}$ M\"ossbauer isomer shift and the surface of the prepeak observed in x-ray-absorption spectra at the Sb ${L}_{\mathrm{III}}$ edge can be linearly correlated because they are both strongly dependent on the Sb $5s$ electron population. Finally, analytical expressions of the numbers of Sb and S valence electrons are derived from simple molecular calculations. These expressions provide rather simple explanations for the observed main trends in the variations of the experimental results in terms of local structural changes.

Nanometric Si/C/N powders have been obtained from the laser synthesis of a liquid precursor: hexamethydisilazane. The chemical composition of the products is a function of the experimental parameters: the C/N ratio in the powders is controlled in the range 0.34 to 1.34 by varying the ammonia content in the flowing gas (argon). This paper presents some results obtained by X-ray Photoelectron Spectroscopy (XPS) about the local atomic structure of these powders. The evolution of the powders after annealing treatments at 1500 and 1600 °C under nitrogen atmosphere has been studied. The chemical composition deduced from XPS wide spectra are compared with chemical analysis. From the analysis of the Si-2p core level, information about the local atomic bonding around silicon atoms are obtained. The different environments present in the system and their evolution with temperature have been deduced from the comparison with data obtained for stoichiometric compounds (SiC, Si 3 N 4 and SiO 2 ). The existence of local chemical disorder is shown in the as-formed powders. For powders with C/N 0.6, the samples remains amorphous until 1500 °C; crystallization which starts around 1500 °C is total at 1600 °C. The existence of C-N bonds at 1500 and 1600 °C is evidenced. This result is in good agreement with results obtained by neutron diffraction and X-ray absorption (XAS).

The total and partial densities of states of , and have been calculated using a scalar relativistic self-consistent augmented plane-wave method () or a self-consistent linear muffin-tin orbital method in the atomic sphere approximation ( and ). The x-ray photoemission valence band and soft-x-ray emission Si K and Ni L spectra have been calculated by applying appropriate broadening factors to the theoretical densities-of-states curves; in the case of the x-ray photoemission spectra, photoionization cross sections have been taken into account. Very good agreement is found between the experimental x-ray photoemission and soft-x-ray emission spectra and the simulated spectral curves.

In order to obtain information about the density and energy distribution of the π states introduced by the sp 2 carbon sites in hydrogenated amorphous carbon (a-C:H) films, we have combined X-ray (XPS) and ultraviolet (UPS) photoelectron spectroscopy experiments with optical measurements in the 0.5–6 eV spectral range. Attention has also been paid to plasmon losses from both XPS and optical data. The results obtained on two series of a-C:H films prepared by the same plasma technique but presenting different optical gaps (2.9 and 1.6 eV respectively) are compared and discussed in relation to the sample microstructure.

X-ray photoelectron spectroscopy experiments were performed on as-deposited evaporated a-Ge x Se100-x compound films, with x ranging from 20 to 50 at.%, in order to investigate the changes in the core level and valence band electron distribution as a function of composition. The results are interpreted in terms of short-range ordering, taking the stoichiometric a-GeSe2 compound as a reference. The valence band spectra are compared to theoretical predictions and discussed in relation to optical data obtained on the same samples. It is shown that 4:2 coordination is maintained over the whole composition range, and that chemically ordered structural units are favoured in all cases.

The local order in Plasma-Enhanced Chemical Vapor Deposition (PECVD) N-rich a-SiN x :H films is shown to depend strongly on the H bonding configuration. The SiH bonding affects the SiN lattice vibration, giving a shoulder at 1020 cm −1 , and shifts the Si3p - N2p peak position in the valence band distribution towards lower binding energies.

The density of valence states of amorphous hydrogenated silicon-nickel a-Si 1−y Ni y :H alloys has been experimentally investigated by soft X-ray emission (SXS) and optical spectroscopies. By SXS, partial Si 3p and Ni 3d valence states are obtained on a common energy scale referred to the Fermi level. Our results show that, as the Ni content is increased, the uppermost valence band changes from Si 3p to hybridized Si 3p-Ni 3d states, leading to a finite density of states at the Fermi level. The results are discussed in relation to optical measurements performed on samples deposited at the same time.

The present paper analyzes the adhesion mechanisms of a silicon oxide film on a polycarbonate substrate, combining XPS, UV-visible ellipsometry and Fourier transform infrared phase-modulated ellipsometry (FTPME) measurements. In particular, we present the new FTPME technique: Due to its submonolayer sensitivity to vibrational properties, it suits well to physico-chemical studies, such as plasma-surface interactions. A preliminary plasma treatment of the polymer substrate before film growth is found to increase the sticking of the first monolayers of the film, and therefore its adhesion, as shown by conventional thermal adhesion tests. The treatment consists of three successive steps: argon plasma, (NH3, Ar) plasma and (SiH4, He, Ar) plasma. The first two steps induce a densification of the bulk and an activation of the surface (formation of CN bonds), while the silane plasma leads to the growth of a very thin silicon oxide layer. In particular, the increase in the film adhesion appears to be closely related to the presence of a SiO vibrational mode located at 1030 cm−1.

A comparative study of two series of a-C:H films prepared by different techniques and presenting strongly contrasting properties was carried out using several complementary techniques probing the electronic density of states and the incorporation of hydrogen. The results were analysed using a two-phase model consisting of π-bonded clusters embedded in an amorphous sp3 C:H matrix. It is shown that the two series differ essentially in the sizes of the clusters and in the degree of confinement of the π electrons within the clusters, and that hydrogen plays a significant role in the film microstructure and its modifications upon annealing.

The chemical bonding and local order in Si, Si‐N, Si‐C, and Si‐C‐N nanometric powders prepared by laser synthesis have been investigated by using two experimental methods. The local environment of Si, C, and N atoms have been studied by x‐ray‐induced photoelectron spectroscopy, from a detailed analysis of the Si 2p, C 1s, and N 1s core levels. Complementary information concerning the structural arrangement around Si atoms has been deduced from extended x‐ray‐absorption fine‐structure analysis performed at the Si K edge. The results show that the Si and Si‐C powders prepared with a 600 W laser power are pure, well‐crystallized materials; the Si‐N sample prepared with the same laser power has a disordered structure, although chemical order exists. For the composite samples, the results reveal that, in particular preparation conditions, a local C‐Si‐N3 structure is formed.

The electronic structure of SiC prepared by synthesis from vapour phase reactants heated with a high power CO 2 laser has been investigated. From an analysis of the photoelectron C 1s and Si 2p core levels we show that only heteropolar SiC bonds are present in the materials, without segregation tendency. The total and partial Si 3p valence band distributions are studied by photoelectron and X-ray emission spectroscopy respectively. The general shape of the valence band is that of a chemically ordered sp 3 -bonded network. The positions of the conduction states relative to E f are obtained from the Si K photoabsorption spectrum.

In order to better understand B(CH3)3 doping effect on a-Si:H characteristics, the local Si bonding have been studied by XPS in B(CH3)3 or B2H6 doped a-Si:H and a-Si1-xCx:H respectively. The results have been correlated to ellipsometry measurements. Boron is found to enhance the incorporation of C in the films; B(CH3)3 largely changes the film growth and the optical properties of the material. These effects can not be attributed to individual B and C effects.

The optical properties of evaporated amorphous GeSe 2 films have been determined before and after annealing by transmission and photothermal deflection spectroscopy measurements. The results are analyzed together with those of X-ray photoemission and X-ray diffraction experimemts. The annealing effects are related to changes in medium-range order. The low-energy optical absorption shows a defect state density varying with deposition conditions and annealing

A comparison between experimental and theoretical densities of states (DOS) is performed for CoSi2. Partial DOS of CoSi2 are studied by soft X-ray spectroscopy (SXS) through Si K beta (3p to 1s) and Co L alpha (3d to 2p32/) emission bands. In addition, X-ray photoemission spectroscopy (XPS) measurements of the valence band are presented. On the theoretical side, a scalar relativistic self-consistent augmented plane wave calculation is performed from which the partial DOS are obtained. The theoretical DOS, with a Lorentzian broadening, are compared with the experimental results and found to be in good agreement.

A study by X-ray photoelectron spectroscopy (XPS) of the local atomic environment in laser-synthetized Si/C/N nanopowders is presented. The Si 2p, C Is, and N 1s core levels as well as the valence band distribution are investigated. The attention is focused on samples with C/N atomic ratio around 0.6 which exhibit interesting properties concerning annealing treatments. The presence of C-N bonds after 1500°C annealed samples is evidenced.

On rapporte les spectres d'emission des rayons (raie Kβ de Al) et d'absorption des rayons X (raie K de Al) du monocristal AlSb. La plupart des structures spectrales sont bien decrites en termes des densites d'etats de valence et de conduction dans un cadre monoelectronique, en negligeant l'interaction electron-trou. Observation d'un exciton de cœur lie, dans le spectre d'absorption, avec une energie de liaison de 0,2 eV. Son intensite est remarquablement inferieure a celle de l'exciton Al2p dans le meme compose. Ceci montre que les regles de selection dipolaires gouvernent la formation des excitons Al11 et Al2p. Construction d'une densite empirique des etats de valence pour AlSb a partir des resultats experimentaux disponibles

Les proprietes d'interfaces al/inp (hauteur de barriere, distribution d'etats d'interface et densite d'etats de valence du phosphore et de l'aluminium) preparees par differentes manieres (clivage sous ultra-vide ou a l'air, nettoyage chimique suivi ou non d'un bombardement ionique de faible energie et traitement thermique) ont ete etudiees en couplant des methodes electriques: caracteristiques i-v, c-v et spectroscopie de capacite schottky (scs) et une methode physico-chimique: spectroscopie d'emission x induite par electrons (exes). Les spectres d'exes montrent que de fortes perturbations de l'inp sont induites par les differentes methodes de preparation. Ces perturbations sont detectees dans la zone interfaciale analysee qui est de l'ordre de 100 a. Elles sont dues a differents phenomenes: existence de liaisons pendantes (clivage sous ultra-vide), inhomogeneites structurelles (clivage a l'air), amorphisation (nettoyage chimique), presence d'aip et/ou incorporation d'argon (bombardement ionique). Cependant, malgre ces modifications physico-chimiques de la zone interfaciale, la barriere de schottky reste confinee dans une gamme etroite de valeurs (0,35-0,5 ev). Ceci est attribue a la presence systematique d'un etat localise mis en evidence dans le gap par scs en e#c-0,37 ev

The results of a detailed study of the effects of disorder and defects on the core level and valence band distributions in amorphous GaAs by X-ray photoelectron spectroscopy, are discussed and compared to those of similar experiments on amorphous Ge. We analyse the differences between the compound and the element in terms of medium-rangedisorder and we study the annealing effects. In the GaAs case, we show evidence for states associated with AsAs wrong bonds, in agreement with theoretical predictions.

The Mo 4d and Si 3p electronic distributions of MoSi2 single crystals prepared by the Czochralski technique are studied separately by soft X-ray spectroscopy (SXS) through the Si Kβ (3p → 1s) and Mo Lβ2 (4d → 2p 3 2 ) emissions. The Fermi energy EF is positioned on by combining XPS and SXS measurements. The Si 3p states are found to be split into two components; one of them, located 2.3 eV below EF is strongly mixed with the Mo 4d states. The SXS results completely agree with the recent calculation of partial densities of states of [8].

A model of hydrogenated amorphous silicon based on the tight-binding coherent-potential approximation method is used to calculate the densities of states and the X-ray spectra of a-Si1-xGex:H alloys. For the first time a quantitative comparison between calculated and measured X-ray spectra is made which reveals good agreement.

Hydrogenated silicon-carbon films prepared by glow discharge from silane-methane mixtures at low power density are used as a model system for the analysis of optical properties and band structure of amorphous tetrahedral semiconductors. Between 0 and 20 at. % of carbon in the solid, the optical gap and the static refractive index can be varied over a wide range without changing the chemical structure of the solid and its good semiconducting properties. The optical constants are well described by a simple two-band model of optical transitions, and the information on the band structure in the solid is condensed into one parameter, the average gap ${E}_{M}$, which corresponds to the energy difference between the centers of gravity of the valence and conduction bands. This value is very close to the energy spacing of the maxima in the distributions of the conduction and valence band deduced from soft-x-ray spectra, and exhibits a similar increase with carbon content. Beyond a carbon concentration of about 20 at. %, we observe a change in the nature of the material. The average gap ${E}_{M}$ increases much more rapidly than the optical gap; x-ray photoelectron spectroscopy indicates an incorporation of carbon in the form of Si-C-Si units in a tetrahedral network, whereas for concentrations smaller than 20 at. % the carbon is mainly incorporated as methyl groups ${\mathrm{CH}}_{3}$.

K X-ray emission and absorption spectra of crystalline and amorphous silicon have been analysed and compared to band structure calculations. The experimental results confirm the influence of rings and bound-angle fluctuations on different regions of the valence and conduction band of amorphous silicon.

The electronic density of states of flash-evaporated amorphous In 1−x P x films, with x > 0.5, is investigated in detail by X-ray photoelectron spectroscopy and by combined optical and photothermal deflection measurements. The results are analyzed in terms of structural and chemical defects, in relation with the predictions of recent theoretical work.

XPS measurements are used to compare the As and Ga core level spectra and the valence band spectrum of flash-evaporated stoichiometric amorphous GaAs to those of crystalline GaAs. The core level data suggest that the amorphous compound is essentially chemically ordered. The most prominent modifications of the valence band due to disorder are a broadening of the upper p-bonding peak, with a parallel shift upwards of the upper edge of the band, and a filling up of the valley between this peak and the intermediate one. The ionicity gap is maintained and the s-like lower peak is little affected.

A data‐acquisition system, controlled by an Apple IIe microcomputer, designed for a bent crystal, vacuum spectrometer is described. A specific interface performing the photon counting via a programmable counter timer and the detector position encoding through a 12‐bit analog‐to‐digital converter is coupled to the microcomputer bus by an 8‐bit parallel interface. An outline of the software in advanced and machine language is given.

The effects of alloying on the density of states near the band edges and in the pseudo-gap in a-Si 1−x Ge x :H alloys with O ⩽ x ⩽ 1 prepared under identical conditions by glow discharge decomposition of SiH 4 /(GeH 4 + H 2 ) mixtures, have been investigated by combining photothermal deflection spectroscopy and soft X-ray spectroscopy. A tentative model for defect-related states is deduced from the data.

An XPS study of the Si 2p and N1s core levels and of the valence band of a-SiN x :H samples prepared by 254 nm Hg photo CVD is presented. From the Si 2p study, various SiN x configurations are evidenced, the SiN 4 unit being predominant for x ⪆1 . The N1s core level modifications are interpreted in terms of H n NSi m configurations. At the top of the valence band, the Si 3p states from SiSi bonds are progressively replaced by N 2p states due to SiN bonds.