Michael J. Tricker

Electronic structure of the oxides of lead. Part 2.—An XPS study of bulk rhombic PbO, tetragonal PbO, β-PbO2 and Pb3O4

XPS studies of the bulk oxides of lead reveal no clear evidence for the presence of the expected two oxidation states of lead in Pb3O4. They also show that the Pb 4ƒ binding energies of the two crystallographic modifications of lead monoxides are the same, within experimental error, but are greater than those for β-PbO2. These results are discussed in the light of lattice potential calculations.

Conversion Electron Mössbauer Spectroscopic study of iron containing surfaces

The early stages of the oxidation of plain carbon steels has been studied by 57Fe Conversion Electron Mossbauer Spectroscopy (CEMS). The potential of the technique in elucidating the nature of new surface—and sub-surface—phases formed on massive solid samples is demonstrated. The measurement of the attenuation of conversion electrons in iron-coated stainless steel substrates is shown to lead to a method whereby the thickness of the oxide films on iron may be estimated. Films of iron oxide containing 57Fe in natural abundance (ca. 2 %) may be readily studied in situ in the thickness range 5 to 500 nm.

The hydrogen and oxygen content of self-supporting carbon foils prepared bydc glow discharge in ethylene

Abstract The hydrogen and oxygen content of self-supporting carbon films produced bydc glow discharge have been determined using a precise method involving the elastic scattering of 25 MeV α-particles. The number of carbon-hydrogen bonds has been determined for similar samples using infra-red spectroscopy. The results are compared with those for samples made by the carbon arc process. Assuming that the glow discharge carbon contains graphitic regions surrounded by amorphous tetrahedrally bonded material to which hydrogen can attach, a simple estimate is made of the relative numbers of carbon atoms in the two forms.

Determination of the hydrogen content of a-Si films by infrared spectroscopy and 25 MeV α-particle elastic scattering

The simultaneous hydrogen and silicon atom densities in amorphous silicon, a-Si, films prepared by the glow discharge technique have been measured by 25 MeV alpha -particle elastic scattering. Integrated band intensities for the silicon-hydrogen stretching modes, omega 1s and omega 2s, in the region 1800 to 2200 cm-1 were determined for the same freely supported films. A similar analysis has been carried out for the bands observed at 890, 840 and 640 cm-1. Effective oscillator strengths for the omega 1s and omega 2s modes in a-Si films have been estimated and compared with the current theories on the effect of the silicon matrix on the infrared absorption characteristics.

Studies of the mechanism of the decomposition of hydrogenated a-Si films

Abstract The dehydrogenation of glow-discharge deposited a-Si films has been studied by in situ infrared spectroscopy in order to resolve the apparent inconsistency between the interpretation of previous manometric data and the assignments of the infra-red spectral features in these films. Our studies show that, on heating at about 350°C, there is no preferential reduction in the integrated band intensities near 2090 cm−1, assigned to =SiH2 stretching modes, relative to the band near 2000 cm−1 assigned to the ≡SiH stretching mode. Accepting both infrared assignments our data conflicts with previous proposals that the low temperature dehydrogenation mechanism involves ≡SiH2 groups alone. It appears that the low temperature dehydrogenation proceeds via the molecular elimination of hydrogen from regions in the film where bound hydrogen atoms are in close proximity. These hydrogen atoms may be incorporated either as monohydride or dihydride groups. The model, therefore, allows a consistent interpretation of t...

Surface and intercalate chemistry of layered silicates. Part II. An iron-57 Mössbauer study of the role of lattice-substituted iron in the benzidine blue reaction of montmorillonite

Direct 57Fe-Mossbauer-spectroscopic evidence is presented for the involvement of lattice-subsituted iron(III) as an electron-accepting site, within montmorillonite, following intercalation of the clay by benzidine which results in the production of benzidine radical cations. The subsequent oxidation of the resulting iron(II), by dehydration of the benzidine blue–montmorillonite intercalate, is explained in terms of two simple equilibria which are set up at the clay surfaces. New Lewis-acid sites [involving iron (III)], created by oxidation of the original (ironII) ions in the clay, have been found to be active even under conditions where it is expected that benzidine species are present only at external surfaces of the montmorillonite.

Conversion electron Mössbauer spectroscopy and the study of surface properties and reactions

Abstract Unlike transmission Mossbauer spectroscopy which, in order to be of widespread utility in surface science, requires high-area solids, conversion electron Mossbauer spectroscopy (CEMS) is applicable to a wide range of low-area materials containing iron (or tin). The necessary conditions required for optimal detection of internally converted electrons (which are emitted from distances of ca. 300 nm below the exterior surface) are outlined, and the surface sensitivity of the technique demonstrated by reference to, inter alia, the determination of the rate coefficient of the parabolic oxidation rate of iron at 500°C and the detection of goethite as a weathering product of the mineral siderite. The application of this technique to other problems in materials science is discussed, and factors governing the characteristics of depth-profiling of specimens of oxidized or corroded iron (or iron-containing material) are discussed by reference to an energy analyzing spectrometer, the essential features of which are described. The merit of acquiring depth sensitive CEM spectra is illustrated by reference to the detection of a doublet which is associated with the iron/oxide interface.

Thermal dehydrogenation of glow discharge a-Si

Abstract Infra-red spectroscopic studies have been made of glow-discharge hydrogenated amorphous silicon films prepared under a variety of experimental conditions. Other studies have been made of the thermally induced dehydrogenation of these films and a model is suggested to account for their mode of decomposition.

57Fe and 119Sn Mössbauer studies of electron exchange processes in spinels of composition Zn2+[Zn(1−x)22+Sn(1+x)24+Fe(1−x2+]O4

Abstract Phases in the spinel series Zn2+[Zn (1−x) 2 2+Sn 1+x 2 Fe1−x3+Fex2+]O4 have been prepared and studied by 57Fe and 119Sn Mossbauer spectroscopy. For 0 ⩽ x ⩽ 0.75 the spinels remain paramagnetic down to 80 K. Evidence is found for fast localized electron hopping between adjacent Fe2+ and Fe3+ ions and also for the complete delocalization of electrons into a conduction band. A model which quantitatively accounts for this latter phenomenon is presented.

57Fe Mössbauer spectroscopic studies of electron-hopping processes in vesuvianites

Abstract Room temperature and liquid-nitrogen temperature 57 Fe Mossbauer spectra of a number of vesuvianite crystals are reported. Certain of the spectra contain doublets whose parameters are intermediate between those normally associated with Fe 2+ and Fe 3+ ions in oxide environments. These doublets are attributed to electron-hopping processes between Fe 2+ ions and adjacent Fe 3+ or Ti 4+ ion.