Chemisorption-induced Pt 4f surface core level shifts

Soft X-ray photoemission experiments have led to the unambiguous observation of a metal surface core level ($\text{Pt}\text{4}\text{f}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}$) shift, due to an adsorbate (CO), to a binding energy larger than the bulk binding energy. The $\text{4}\text{f}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}$ clean (110) surface component, with a binding energy 0.35 ± 0.02 eV lower than the bulk, is shifted by 1.06 ± 0.04 eV towards higher binding energy upon CO chemisorption. The lack of significant changes in the bulk component indicates the localized nature of the CO-Pt surface bonding.     

Photoemission study of Tm metal

A photoemission investigation of Tm metal has been carried out using photon energies in the 100–200 eV range. Electron energy distribution curves and the photon absorption coefficient has been measured and the results are compared to earlier XPS and absorption measurements. No evidence of a valence change at the surface of Tm metal was found, a posibility proposed earlier.     

Phase preparation in steady-state free precession MR elastography

Strain and motion measurements in balanced steady-state free precession (bSSFP) imaging require high magnetic field homogeneity. This requirement is due to the nonlinear signal response to spin phase variations in bSSFP. Here, a technique that utilizes background gradients for preparing strong in-plane spin phase variations is proposed. As a result, periodic patterns of increased motion sensitivity appear, which are interleaved with bands of low phase-to-noise ratio. Spatial filters commonly used in MR elastography (MRE) remove these bands and leave wave images equivalent to a uniform phase response in bSSFP-MRE. Since phase preparation gradients locally enhance motion sensitivity, the technique can be employed for selectively increasing the wave signal amplitude in MRE. The method is applied without the need for previous shimming, which reduces the examination time. In vivo phase prepared bSSFP-MRE is demonstrated in human liver and heart.     

Valence band studies of clean and oxygen exposed GaAs(100) surfaces

We found, by correlating band bending, ultraviolet photoemission spectroscopy, and partial yield spectroscopy measurements, that Fermi level pinning at midgap of n-type GaAs(110) is caused by extrinsic states. The exact nature of these states is not yet clear, but the surfaces with Fermi level pinning were strained as evidence by a smeared valence band emission. This smearing was removed by as little as one oxygen per 10⁴ to 10⁵ surface atoms. This implies that the oxygen has very long range effects in causing spontanesous but small rearrangement of the surface lattice and removing surface strains. When about 5% of a monolayer of oxygen is adsorbed, a major change in the electronic structure takes place. Again, the oxygen coverage is very small, which suggests long range effects now leading to a fairly large rearrrangement of the surface lattice. Finally, from comparing the oxygen induced emission for exposures greater than 10⁷ L O₂, with the spectra from gas photoemission measurements on molecular oxygen, we suggest that the oxygen is chemisorbed as a molecule on the (110) surface of GaAs.     

Oscillations in the compositional depth profile of Cu/Ni alloys: A study by UPS

The composition in the surface region of a (110) oriented single crystal of Cu/Ni alloy was studied by ultraviolet photoemission spectroscopy (UPS) in the energy range hv = 32–240 eV. The data indicate a surface enrichment of Cu and that the composition, as a function of depth below the surface, does not approach the bulk value in a monotonic manner but shows at least one oscillation. The depth sampled by the UPS experiment was varied by changing the photon energy and thus the escape length of the photoemitted electrons. Two surfaces of a single bulk crystal (bulk atomic composition 90% Ni and 10% Cu) were studied. One was the high temperature equilibrium surface (AES measurements yielded a surface composition of ~65% Cu and 35% Ni); the second surface was higher in Ni concentration (AES measurements gave ~65% Ni and 35% Cu) and was obtained by annealing at a lower temperature. Theories based on the quasi-chemical and regular solution models predict a surface enrichment of Cu for the alloy, but do not predict any oscillation in composition below the surface.     

Photoemission studies of clean and oxidized Cs

Photoemission studies of the oxidation of Cs at ～ 140 K have been carried out. Four different states of oxygen were observed. Definitive identification of three of the four states has been achieved in two steps: (1) comparison of the multiplet structure of free oxygen ions and the multiplet structure in the photoemission spectra of oxygen sorbed in Cs (i.e., comparison of the energy separations of the various oxygen levels involved); and (2) comparison of experimentally measured binding energies of various states of oxygen with calculated binding energies of known oxygen species inserted in Cs. The oxygen species identified are O^2?, O₂^2? and O₂^?. The multiplet structure of O₂^2? in Cs is identical to that expected for free O₂^2? with no differential relaxation of orbital energies. In contrast, significant differential relaxation in orbital energies is observed for O₂^? in Cs. This difference is attributed to the closed-shell and open-shell configurations of O₂^2? and O₂^?, respectively. The oxidation-induced changes in the Cs 4d, 5s and 5p core levels and the NOO and OVV Auger transitions have also been studied in detail. A discussion of the oxidation of Cs, based on the oxygen species identified definitively, is also given.     

The equivalence theorem and effective Lagrangians

We point out that the equivalence theorem, which relates the amplitude for a process with external longitudinally polarized vector bosons to the amplitude in which the longitudinal vector bosons are replaced by the corresponding pseudo-Goldstone bosons, is not valid for effective Lagrangians. However, a more general formulation of this theorem also holds for effective interactions. The generalized theorem can be utilized to determine the high-energy behaviour of scattering processes just by power counting and to simplify the calculation of the corresponding amplitudes. We apply this theorem to the phenomenologically most interesting terms describing effective interactions of the electroweak vector and Higgs bosons in order to examine their effects on vector-boson scattering and on vector-boson-pair production in $f\bar f$ annihilation. The use of the equivalence theorem in the literature is examined.     

Separation of a glycosylated and non-glycosylated fraction of caseinomacropeptide using different anion-exchange stationary phases

Caseinomacropeptide (CMP), a heterogeneous group of peptides regarding the degree of glycosylation and phosphorylation, has so far not been effectively fractionated into its two major fractions: the glycosylated gCMP and the non-glycosylated aCMP. Therefore, an anion-exchange chromatography (AEC) process for the fractionation of CMP in those two fractions was developed and optimized. Furthermore, the method was applied to compare membrane adsorption chromatography (MAC) devices with classical bead-based column chromatography. It was shown that MAC devices can separate gCMP from aCMP, however, at a lower level of binding capacity and chromatographic resolution compared to classical chromatography. On the other hand, a fractionation is achieved at a four times faster separation speed.     

[2,3] Sigmatropic rearrangement of S-(3-chloroallyl) thiocarbamate sulfoxides followed by a 1,2-elimination reaction yielding unsaturated aldehydes and acid chlorides

Peracid oxidation of $\text{S}$-(2,3-dichloroarryl) was $\text{S}$-(2,3,3-trichloroallyl) thiocarbamates yields 2-chloroacrolein and 2-chloroacrylyl chloride, respectively, via intermediate $\text{S}$-allyl thiocarbamate sulfoxides and $\text{S}$-$\text{O}$-allyl thiocarbamate sulfenate esters.