X-ray Induced Photoelectron Spectroscopy Research Articles

Experimental electronic structure studies of La2?x Sr x CuO4

X-ray induced photoelectron spectroscopy, bremsstrahlung-isochromat spectroscopy, and electron energy-loss spectroscopy were used to investigate the electronic structure of the high-temperature superconductor La2−xSrxCuO4. In general, good agreement was obtained with band structure calculations of the tetragonal phase of La2CuO4. Near the Fermi energyEF the systems shows forx=0 a smeared out gap or a region of very low density of states ∼2eV wide. Upon replacement of La by Sr, the gap is filled with defect states, the intensity of which is proportional tox. The experimental data are not consistent with the closing of a Peierls gap alone.

On the role of potassium additives in the chlorination of TiO 2 by CCl 4 and COCl 2

The role of potassium present on the surface or even built into the bulk has been studied in the chlorination of titanias by CCl 4 and COCl 4 to volatile TiCl 4. The solids to be chlorinated were characterized by atomic absorption spectroscopy (AAS) and X-ray induced photoelectron spectroscopy (XPS) and the kinetics of the reaction was followed by thermogravimetry (TG). In case of COCl 2 a catalytic effect of potassium was observed whereas, when chlorinating with CCl 4, potassium additives resulted in a strong retardation of the reaction. The results are interpreted in terms of the electronic structure of the solid surfaces and the different polarizability of the reactants.

Experimental Electronic Structure Studies of the High-Temperature Superconductors La2-xSrxCuO4 and Ba2GdCu3O7-y

X-ray induced photoelectron spectroscopy (XPS), bremsstrahlung-isochromat spectroscopy (BIS), and electron energy-loss spectroscopy (EELS) were used to investigate the electronic structure of La2-xSrxCuO4. The samples with x=0 show near the Fermi energy a smeared out gap or very low density of states in a region of ∼2 eV. Upon replacement of La by Sr, this gap is filled with defect states, the intensity of which is proportional to x. Similar spectra were observed for Ba2GdCu3O7-y (TC=94K). This may indicate, that the density of states near EF in this compound may be related to defects on the O sites too.

Influence of disorder on the electronic distribution of InP by X-ray and photoelectron spectroscopies

Soft X-ray spectroscopy (SXS) and X-ray induced photoelectron spectroscopy (XPS) measurements have been performed on amorphous InP samples prepared by flash evaporation, comparatively to crystalline InP. SXS results reveal striking differences in the 3p states of the valence band distribution of a-InP as compared to c-InP. The presence of a partial chemical disorder in a-InP is deduced from XPS measurements.

Carbon in olivine single crystals analyzed by the 12C(d, p) 13C method and by photoelectron spectroscopy

Carbon subsurface concentration profiles in olivine single crystals from San Carlos, Arizona, and the Sergebet Island. Red Sea, containing total carbon between 60–180 wt.-ppm, were analyzed by means of the 12C(d. p) 13C nuclear reaction and by x-ray induced photoelectron spectroscopy (XPS) in combination with acid etching and with Ar + ion sputtering respectively, between 200–930 K. The (d, p) analysis reveals equilibrium subsurface C profiles extending 1–2 μm or more into the bulk. Their steepness is a function of temperature. Typical mean C concentrations at 300 K in the resolvable layers, 0–0.6, 0.6–1.2, and 1.2–1.8 μm. are 1.8, and 0.6 wt.-%, corresponding to enrichment factors over the mean bulk C concentration of the order of 100, 40 and 30 respectively. In the topmost atomic layers analyzed by XPS the carbon is enriched by a factor of the order of 1000, decreasing with increasing temperature. The results suggest that the carbon is in a truly dissolved state and highly mobile, subject to a reversible subsurface segregation. Most probably local lattice strain associated with the solute C species provide the driving force for this diffusional process. The C diffusion coefficient was determined from the (d, p) data below 300 K: D= 10 −13 exp(−7.8/RT) [m 2· sec −1; KJ · mole −1] and from XPS data between 450–925 K: D = 10 −14 exp(-6/RT) [m 2 · sec −1; KJ · mole −1] The estimated error of the preexponential factors is ± one order of magnitude, that of the activation energies ±3.5 and ±2 KJ mole −1 respectively.

Polaromicrotribometric (PMT) and Spectroscopic (Infrared‐XPS) Study of the Formation and Modifications of Films Formed on a Polarized Platinum Electrode in THF ‐ LiClO4 Medium: I . Cathodic Polarization

The mechanism of formation and the changes of different deposits obtained on a Pt cathode in medium are studied by means of polaromicrotribometry (PMT). Their chemical nature is determined by infrared and x‐ray induced photoelectron spectroscopy (XPS). For a polarization between −1.6 and −2.5V, a thin porous homogeneous film of lithium hydroxide occurs, which is characterized by a low friction coefficient , where is the value in the absence of polarization. Small amounts of carbon dioxide in solution react on lithium hydroxide and convert it into lithium carbonate. This chemical change provokes a strong increase in the friction coefficient ( rises from 0.7 to 2 ) and is marked by the appearance of a very regular stick‐slip phenomenon. Under galvanostatic control and at a weak electrolysis current, the formation of lithium hydroxide and then lithium metal is successively observed. The friction curves clearly show that Li+ ions migrate through the porous lithium hydroxide layer and are reduced on the metal surface. When electrolysis is continued over a longer period of time the lithium hydroxide layer is coated with lithium metal. At a higher current density and at a lower water concentration, a layer of metallic lithium can be obtained in the electrode surface without the prior formation of lithium hydroxide.

X-ray analysis of particulate matter collected in an environmental monitoring device.

X-ray induced photoelectron spectroscopy, energy dispersive X-ray fluorescence spectroscopy and X-ray diffraction techniques are used in conjunction to give routine qualitative and semi-quantitative elemental and chemical analyses of airborne particulate matter collected in an environmental monitoring device. The advantages and disadvantages of each technique are discussed and examples are given of typical analyses of samples of particulate matter weighing down to 100 µg. The results from the first two techniques are complementary but X-ray diffraction does not often give the unequivocal structural information expected.

Mechanism of the interaction of hydrogen sulphide with adsorbed oxygen on lead studied by X-ray induced photoelectron spectroscopy

The interaction of hydrogen sulphide with lead films which have chemisorbed oxygen has been investigated in the temperature range 80 to 290 K by X-ray induced photoelectron spectroscopy. Removal of oxygen is complete at 290 K with its replacement by a surface sulphide. At lower temperatures intermediate steps in the surface reduction process have been isolated. An unambiguous interpretation of previously published work function and adsorption data is now possible.

The surface and intercalate chemistry of the layered silicates. Part IV. Crystallographies electron-spectroscopic, and kinetic studies of the sodium montmorillonite–pyridine system

Neutron-diffraction studies of the stable pyridine (py) intercalate of Na+-exchanged montmorillonite [basal-spacing 14.8 Å, idealized formula Na+0.5(Al3.5Mg0.5)Si8O20(OH)4·py·2H2O] have been carried out. It is shown that the plane of the guest aromatic molecule is perpendicular, and the long (C–N) axis inclined at 60°, to the aluminosilicate sheets. The kinetics of the conversion of the initially formed less-stable intercalate [basal-spacing 23.3 Å, idealized formula Na+0.5(Al3.5Mg0.5)Si8O20(OH)4·(py)2·H2O] to the more stable 14.8 Å intercalate has been followed by X-ray diffraction. X-Ray induced photoelectron spectroscopy (x.p.s.) has also been used to probe electronic changes in the environment of the Na+ ions following intercalation. X.p.s. shows that the pyridine is retained even in vacua of 10–6 N m–2 at room temperature, and that the nitrogen atoms are situated within essentially one type of environment.

Kinetics of the formation of graphite oxide

The retention of ethylene glycol and X-ray-induced photo-electron spectroscopy (XPS) have been used to follow the oxidation process of two different types of graphite, a natural based and an artificial one. From both methods it is apparent that the oxidation process is almost complete by about 24–32 hr. The specific velocity of the oxidation process has been calculated from both methods, giving values in reasonable agreement; consequently it appears that these methods are consistent when the oxidation kinetics are deduced. In all cases the amount of oxygen and the specific velocity in graphite oxide from the artificial graphite is higher than that in graphite oxide from the natural based one.

Band structure and photoemission studies of SnS2and SnSe2. I. Experimental

Ultraviolet and X-ray induced photoelectron spectroscopy studies have been carried out on single crystals of SnSe2 and SnS2. Basal surfaces of both materials are inert and have photothresholds of 5.35 eV and 6.3 eV respectively. The kinetic energy distributions of excited electrons are analysed in terms of existing theoretical band calculations. Good agreement exists between experiment and calculations based on the pseudopotential and tight binding methods.