S. Hardcastle

The nature of hydrogen in x‐ray photoelectron spectroscopy: General patterns from hydroxides to hydrogen bonding

Important progressive alterations in chemical bonding are often realized through correlations with shifts in the x‐ray photoelectron spectroscopy (XPS) binding energies of key elements. For example, there are useful general XPS shifting schemes for such systems as oxides, nitrides, halides, and even various functional groups in organics. Very general patterns, based upon location in the periodic table, exist for many of these materials even when the structure is not strongly considered. Unfortunately, apparently because of the lack of direct XPS detection of hydrogen, there seems to be no general statements in the literature for describing hydrogen‐containing compounds, despite the fact that synergistic shifts obviously exist in the XPS spectra of elements attached to hydrogen (e.g., for M–O–H vs M–O–M units, where M is a typical metal). While not attempting a complete review paper, in the present work we use XPS shifting patterns to evolve a series of interrelated covalency/ionicity arguments to help exp...

Structural effects in single-crystal photoelectron, Auger-electron, and Kikuchi-electron angular diffraction patterns

Abstract The full-hemisphere diffraction patterns of primary photoelectrons, photoemission Auger electrons, and Kikuchi electrons are reported for single-crystal surfaces of Cu(100), Cu(111), Cu(110), Ir(111), and Ag(100), to test models for direct structure determinations from angle-dependent final-state diffraction patterns. Our measurements show a simple correlation between the low-index crystallographic directions of the substrate and local intensity maxima in the electron angular distributions. We find that the angular anisotropy can be qualitatively explained in all cases studied by final-state elastic forward scattering. The strong forward scattering features in photoemission diffraction patterns are used to measure bond angles and determine the structure of Cu ultrathin films on Ir(111). In addition, a radial image function based on a holographic Fourier-transform algorithm is evaluated for the determination of bond lengths from three-dimensional images reconstructed from the two-dimensional diffraction pattern.

Thin polymer films prepared by radio frequency plasma sputtering of polytetrafluoroethylene and polyetherimide targets

Plasma polymerization is a common technique used for the deposition of thin polymer films. Radio frequency (rf) sputtering may also be employed for plasma polymerization with the principal difference being the introduction of fragmented polymer species (for the latter) rather than gaseous monomer species into the plasma. The thrust of this work is to study the integrity of thin films prepared by rf plasma sputtering of two substantially different polymer systems. Polytetrafluoroethylene (PTFE) has a simple linear chain molecular structure and is noted for its lubrication and nonwetting properties. Conversely, polyetherimide (PEI) possesses a complex ring molecular structure and is known for its dielectric strength and high temperature stability. The techniques utilized to characterize the films were x‐ray photoelectron spectroscopy (XPS), DRIFT, UV–Visible, x‐ray diffraction, and scanning electron microscopy (SEM). Periodic controlled ion sputter treatment during XPS analysis of both virgin and sputtered ...

XPS study of the cBN–TiC system

Sintered cubic boron nitride is widely used in various industrial applications because of its extreme wear and corrosion resistance, thermal and electrical properties. In order to obtain composite materials with these optimal properties it is important to elucidate whether chemical reactions occur at boron nitride/bonding phase interfaces. Some of these systems were then subjected to physical and thermal alteration This paper summarizes theoretical and experimental studies on the cBN–TiC 1:1 molar ratio. From theoretical calculations it follows that TiC reacts with boron nitride forming two new phases, TiB2 and TiN. Experimentally CBN–TiC composites were prepared by hot pressing, and the samples were subsequently heat treated. The samples were characterized after heat treatment using transmission electron microscopy and X-ray diffraction.

Surface science lettersX-ray photoelectron holography of ultrathin film and single crystal Cu(111): improving the accuracy of bond-length determination

Abstract Forward-scattering diffraction patterns from single-crystal Cu(111) substrates and an epitaxial film of FCC Cu/Ir(111) have been analyzed to produce real-space images of the atomic lattice by Fourier-transform holography. The accuracy of atomic positions is found to be better in the single-crystal holograms than in the ultrathin film of copper. The angular dependence of the atomic scattering factor produces a shift in the position of atoms in the holographic image, and causes the atom image to be asymmetric. Model calculations reproduce the atom shift and asymmetry. A modified Fourier-transform algorithm is shown to correct for both the atom-shift and the image asymmetry.

Investigations of the surface chemistry of pathogenic silicates

The following is a continuation of our extensive investigations of the chemistry of complex silicate systems employing a combination of electron spectroscopy for chemical analysis and magic angle spinning nuclear magnetic resonance. In this case, we are beginning to provide unique chemical information that may have implications in the field of silicate‐induced pathogenesis (e.g., asbestosis). Select silicate materials (such as amphiboles) have been investigated both before and following alterations of their physical conditions (e.g., crushing) and also before and after contact with certain in vitro cell cultures. In our studies to date, we have been able to track the ‘‘in‐lattice’’ chemistry of the constituents of these, and related, silicates, determining such features as the simultaneous presence of aluminum in tetrahedral and octahedral sites of amphiboles, as well as the iron in M(4), as opposed to M(3) or M(1) octahedral positions of these amphiboles. We are comparing results for fibrous silicates wi...

X-ray photoelectron spectroscopy investigations of the chemistries of soils

The present study continues our x-ray photoelectron spectroscopy (XPS) or electron spectroscopy for chemical analysis investigations of silicate systems, particularly those in contact with biological materials. In the present case, the investigations are extended to a detailed analysis for a wide variety of soil samples extracted from different locations around the world. The samples were selected from relatively pristine sites, pressed into wafers, and were examined without further modification. All of the materials were insulators and therefore analysis required extensive use of the electron flood gun. Careful XPS chemical shift assignments have been achieved for many silicate minerals. These have been exploited in the present study along with the detailed XPS analysis of organofunctional groups rendered by Beamson and Briggs. As a result, a fairly detailed simultaneous nondestructive description is provided of the surface of both the humus and silt components of these soil samples. Substantial variatio...

Effect of anodic treatment on the composition and structure of electrodeposited Zn-Cr alloy coatings

The anodic behaviour of Zn–Cr alloy coatings, containing 14–28 at.% of Cr is investigated in 1 M Na2SO4 solution using electrochemical methods. The alterations of the composition and structure caused by anodic treatment, are examined by means of EDX, XRD, XPS and SEM. Independently of the initial Cr content in the alloys the g-Zn phase and depleted of Cr bcc C-(Zn,Cr) phase are dissolving at potentials more positive than that of Zn. Further dissolution of the C-(Zn,Cr) phase is established at a potential close to the potential of transpassive dissolution of Cr. A thin C-(Zn,Cr) layer, containing about 40 at.% of Cr, remains and is mechanically disintegrated after the potential of oxygen evolution is reached. 2003 Elsevier Ltd. All rights reserved.

Metal uptake in neurone cultures: a systematic study

We present the first comparative study of the uptake of metal ions by neurons, performed for Zn, Cr, Co, Mo, Al, Ni, Mn and Cd. The study reveals substantial differences in the uptake of different metals, under similar exposure procedures. In particular, we found very large uptakes for aluminium and molybdenum. We also found significant effects of excitatory substances, in particular kainate, as stimulants of uptake of some of the metals.

Cryogenic stabilization of high vapor pressure samples for surface analysis under ultrahigh vacuum conditions

A novel form of ultrahigh vacuum (UHV) cryogenic stabilization has been used to obtain high-resolution x-ray photoelectron spectroscopy (XPS) data from a complex amine, 1,8-bis(dimethylamino)naphthalene, whose solid phase exhibited at room temperature an unacceptably high rate of sublimation. Protonated versions of the amine exhibit hydrogen bonding. Electron spectroscopy for chemical analysis chemical shifts can be used to describe the strength and asymmetry of hydrogen bonding formed in proton sponge complexes. Analyzing the binding energy shifts of N (1s) induced by the presence of this hydrogen bonding required obtaining corresponding XPS spectra from the nonprotonated (reference) sample, but the reference sample sublimes under even moderate vacuum conditions. The combined results suggest that other high vapor pressure materials, particularly those that were previously considered to be too corrosive for routine analysis, can be cryogenically stabilized for surface analysis under similar UHV conditions.