Electronic structure of carbyne studied by X-ray photoelectron spectroscopy and X-ray emission spectroscopy

The electronic structure of amorphous carbyne has been investigated by X-ray photoelectron spectroscopy and X-ray emission spectroscopy. Carbyne band structure has been calculated semiempirically and the experimental data have been interpreted on the basis of the calculation results. The valence band width was found to be about 20 eV which is the same as that in all other condensed carbon structures. The fine satellite structure near the 1s line of carbon has been studied. It is shown that the energy bands in carbyne are arranged in a mirror-like way relative to the Fermi level. The real carbyne structure is susceptible to conformations which affect primarily the π-subband structure.     

Electronic structure of red amorphous phosphorus studied by X-ray spectroscopy

A SXS study of occupied and unoccupied 3p states of semiconducting red amorphous phosphorus is presented. It is shown that in the upper part of the valence band, partially hybridized sp spates are present among p pure states, whereas the bottom of the valence band is almost s-like. The results are discussed in connection with theoretical data available for black phosphorus.     

Electronic structure of amorphous Nb1-x Si x films studied by X-ray emission and X-ray photoelectron spectroscopy

We present valence band spectra of the amorphous system Nb_1–x Si _x (0.2x0.8), of bcc-Nb and of a-Si obtained by X-ray photoelectron spectroscopy (XPS, Al K) and X-ray emission spectroscopy (XES, Si K-emission bands). The samples were prepared as thin films by sputtering. The origin of all prominent spectral features was identified and consistently correlated to Si 3s-, Si 3p-and Nb 4d-derived states. The Nb4d-Si3p coupling is stable in binding energy over a wide concentration range. There is strong experimental evidence that the short range order changes considerably within the concentration interval 0.4x0.7, whereas the partial density of states of the Si 3p-electrons is clearly altered in the small concentration range 0.50x0.57.     

Electronic band structure of graphite studied by highly angle-resolved ultraviolet photoelectron spectroscopy

The electronic valence band structure of graphite has been experimentally determined with considerable accuracy for the first time by the highly angle-resolved ultraviolet photoelectron spectroscopy. The photoemission measurements were performed on a synthesized single-crystalline graphite (kish graphite) with the He II resonance line as an exciting source. Some high symmetry points in the Brillouin zone have been successfully identified in the experimentally determined band structure. The present experimental result has been compared with early photoemission experiments and some band calculations presented so far.     

Surface chemistry studied by in situ X-ray photoelectron spectroscopy

Time-dependent X-ray photoelectron spectroscopy is used to study the kinetics and dynamics of simple surface reactions. Combining high-resolution core level spectroscopy with a supersonic molecular beam in one experimental setup, processes such as the dissociative adsorption of methane on both Pt(111) and Ni(111), the coadsorption of water and CO on Pt(111), and the oxidation of CO on Pt(111) have been studied. In the case of methane, the observed vibrational fine structure in C 1s spectra is used to identify the adsorbed species (CH₃) and further thermal dehydrogenation steps. While simple dehydrogenation via CH is observed on Pt(111), a C–C coupling reaction to acetylene is found on Ni(111). In the coadsorbate phase, CO is found to be able to replace predosed water from the bilayer into multilayers. Water, in turn, leads to a site change of the CO molecules, which are preferably adsorbed at bridge sites in the presence of water, as opposed to on-top adsorption on clean Pt(111). For the truly bimolecular surface reaction, the CO oxidation on Pt(111), the ability of the molecular beam to create a relatively high CO pressure was found essential to study the kinetics of the basic step (CO+OCO₂) without influence of adsorption or diffusion rate. An activation energy of 0.53 eV and a preexponential factor of 5×10⁶ s^-1 are found. PACS 68.43.Mn; 79.60.Dp; 82.20.Pm     

Electronic structure of nickel porphyrin NiP: Study by X-ray photoelectron and absorption spectroscopy

Physics of the Solid State - Energy distributions and properties of the occupied and empty electronic states for a planar complex of nickel porphyrin NiP are studied by X-ray photoemission and...     

Electronic structure and bonding in metal hydrides,studied with photoelectron spectroscopy

We present photoemission spectra of various binary and ternary metal hydrides and of some intermetallic compounds. An analysis of these data with respect to the known heats of hydrogen solution in the metals demonstrates two important properties of the metal-hydrogen bond: First we find that core level, shifts in ternary systems are not simply related to those in binary ones. In contrast to a frequently used assumption, metal-hydrogen interaction in a ternary hydride cannot be a pair interaction between the atomic constituents. Secondly, we find from our studies of the valence band spectra of some intermetallic compounds an inverse correlation between the heat of hydrogen solution and the density of states at the Fermi level.We analyse the core level shift data from binary hydrides using the experimental heats of hydrogen solution. We find a very good agreement between calculated and measured core level shifts in transition metal hydrides. However, in rare earth hydrides our approach fails. The reason for this behaviour originates in the photoemission process itself. A thermochemical interpretation of core level shifts can only be successful in the adiabatic limit of core excitation. The systematic behaviour of our results can be explained, if core excitation is considered to be adiabatic in transition metal hydrides but sudden in the rare earth hydrides. We also discuss the impact of such an interpretation on the concepts of adiabatic and sudden core excitation in metals.     

Valence bands of aluminium noble-metal alloys studied by X-ray photoelectron spectroscopy

The valence bands of aluminium noble-metal alloys are studied by XPS using Al Kα-radiation. The alloys were prepared by evaporation followed by interdiffusion of the components under ultra-high vacuum within the analyzer chamber of the spectrometer. In the absence of surface contamination the alloys exhibit more intense spectra, with sharper features, than those observed for previously studied bulk samples.     

Surface defect centres in irradiated AgCl studied by X-ray photoelectron spectroscopy

Irradiation of silver chloride with both UV and soft X-rays during X-ray photoelectron spectroscopic measurements at ca. 300K produces a new thermally-stable chlorine centre; however, at temperatures below ca. 180K the rate of production of this species is immeasurably slow. Cadmium doping experiments indicate that the centre is closely associated with cation vacancies.     

Electronic properties of free and supported metal clusters studied by photoelectron spectroscopy

The electronic properties of free and supported metal clusters are studied by photoelectron spectroscopy. Experimental as well as theoretical results clearly demonstrate a dramatic dependence of the level structure on the cluster size. By this an interesting way might be opened to modify the electronic, optical and chemical properties of surfaces.     

Valence band structure of single crystal titanium carbide,studied by soft X-ray and ultraviolet photoelectron spectroscopy

Valence states of single crystal titatium carbide (TiC_x, X?0.88) have been studied with photon energies ranging from far ultraviolet (u.v.) to soft X-ray. The valence band consists of two peaks located at 3 and 10 eV below the Fermi level. This is in good agreement with recent APW band structure calculations that predict a strong hybridization of the Ti 3d and C 2p bands and a C 2s band at lower energy.     

X射线光电子能谱

X射线光电子能谱（X-ray photoelectron spectroscopy，XPS）技术也被称作用于化学分析的电子能谱（electron spectroscopy for chemical analysis，ESCA）．XPS属表面分析法，它可以给出固体样品表面所含的元素种类、化学组成以及有关的电子结构重要信息，在各种固体材料的基础研究和实际应用中起着重要的作用．文章简要介绍了XPS仪器的工作原理和分析方法，并给出了XPS在科学研究工作中的应用实例．     

Electronic structure of CeAl2 thin films studied by X-ray absorption spectroscopy

We report X-ray absorption near edge structures (XANES) study of CeAl₂ thin films of various thicknesses, 40-120 nm, at Al K- and Ce L₃-edges. The threshold of the absorption features at the Al K-edge shifts to the higher photon energy side as film thickness decreases, implying a decreased in Al p-orbital charges. On the other hand, from Ce L₃-edge spectra, we observed a decrease in the 5d4f occupancy as the surface-to-bulk ratio increases. The valence of Ce in these thin films, as revealed by the Ce L₃-edge spectral results, is mainly trivalent. From a more detailed analysis we found a small amount of Ce⁴⁺ contribution, which increases with decreasing film thickness. Our results indicate that the surface-to-bulk ratio is the key factor which affects the electronic structure of CeAl₂ thin films. The above observations also suggest that charge transfer from Al to Ce is associated with the decrease of the film thickness.     

On the charge distribution in manganese borides studied by X-ray photoelectron and emission spectroscopy

For the borides of the Mn-B system the values of binding energies of Mn 3p, $\text{2p}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$, $\text{2}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ and B1s core levels were measured on an electron spectrometer. Depending on boride composition the variation of inner level energies is very similar, showing a change of sign in the region of the monoboride phase. The same variation has been observed for some characteristics of X-ray emission spectra from these borides. An attempt is made to understand which of the chemical bonding factors are chiefly responsible for a regular concentration dependence of the X-ray and photoelectron spectra.     

Ion bombardment-induced decomposition of Li and Ba sulfates and carbonates studied by X-ray photoelectron spectroscopy

Radiation damage to the surfaces of lithium and barium sulfates and carbonates under 4 ke V Ar⁺ bombardment has been investigated by X-ray photoelectron Spectroscopy (XPS). Damage is readily observed at a dose of 1 × 10¹⁶ ions cm^?2 with saturation occurring over the range 2–8 × 10¹⁷ ions cm^?2. Both valence and core level XPS spectra indicate that, at the saturation dose, the basic sulfate and carbonate structures remain along with decomposition products. Both sulfur and carbon are preferentially lost from all four compounds and oxygen is preferentially lost from both Li compounds but not from the Ba compounds as a result of bombardment. The major decomposition products are the metal oxides with smaller quantities of carbides, sulfides, and SO_n^x?(n = 3,2,1) species.     

Bonds and Fermi surfaces studied by photoelectron spectroscopy

Photoelectron spectroscopy with synchrotron radiation employing high energy and angular resolutions is a very efficient tool for experimental investigations of the electronic structure of solids and their surfaces. In addition to standard band-mapping applications, photoemission intensity and line-shape analyses provide valuable information about wave functions, bonds and interactions of a many-electron system. In this report we choose covalent semiconductor surfaces as well as metallic clean and nanostructured surfaces of layered materials to serve as model systems for assessing the spatial origin of photoelectrons and the three-dimensional shape of Fermi surfaces. Received: 11 July 2001 / Accepted: 23 July 2001 / Published online: 3 April 2002     

Electronic structure studies of the spinel CoFe2O4 by X-ray photoelectron spectroscopy

The spinel CoFe₂O₄ has been synthesized by combustion reaction technique. X-ray photoelectron spectroscopy shows that samples are near-stoichiometric, and that the specimen surface both in the powder and bulk sample is most typically represented by the formula (Co_0.4Fe_0.6)[Co_0.6Fe_1.4]O₄, where cations in parentheses occupy tetrahedral sites and those within square brackets in octahedral sites. The results demonstrate that most of the iron ions are trivalent, but some Fe²⁺ may be present in the powder sample. The Co 2p_3/2 peak in powder sample composed three peaks with relative intensity of 45%, 40% and 15%, attributes to Co²⁺ in octahedral sites, tetrahedral sites and Co³⁺ in octahedral sites. The O 1s spectrum of the bulk sample is composed of two peaks: the main lattice peak at 529.90 eV, and a component at 531.53 eV, which is believed to be intrinsic to the sample surface. However, the vanishing of the O 1s shoulder peak of the powder specimen shows significant signs of decomposition.