[en] Magnetic X-ray Linear Dichroism (MXLD) in Photoelectron Spectroscopy and X-Ray Photoelectron Diffraction (XPD) of the Fe 3p core level have been used to probe the magnetic structure-property relationships of perpendicularly magnetized Fe/Cu(001), in an element-specific fashion. A strong MEXLD effect was observed in the high resolution photoelectron spectroscopy of the Fe 3p at open-quotes normalclose quotes emission and was used to follow the loss of perpendicular ferromagnetic ordering as the temperature was raised toward room temperature. In parallel with this, open-quotes Forward Focussingclose quotes in XPD was used as a direct measure of geometric structure in the overlayer. These results and the implications of their correlation will be discussed. Additionally, an investigation of the effect of Mn doping of the Fe/Cu(001) will be described. These measurements were performed at the Spectromicroscopy Facility (Beamline 7.0.1) of the Advanced Light Source

[en] As modern, technologically important materials have become more complex, element specific techniques have become invaluable in studying the electronic structure of individual components from the system. Soft x-ray fluorescence (SXF) and absorption (SXA) spectroscopies provide a unique means of measuring element and angular momentum density of electron states, respectively, for the valence and conducting bands in complex materials. X-ray absorption and the decay through x-ray emission are generally assumed to be two independent one-photon processes. Recent studies, however have demonstrated that SXF excited near the absorption threshold generate an array of spectral features that depend on nature of materials, particularly on the localization of excited states in s and d-band solids and that these two processes can no be longer treated as independent. Resonant SXF offers thus the new way to study the dynamics of the distribution of electronic valence states in the presence of a hole which is bound to the electron low lying in the conduction band. This process can simulate the interaction between hole-electron pair in wide gap semiconductors. Therefore such studies can help in understanding of transport and optics phenomena in the wide gap semiconductors. The authors report the result of Mn and S L-resonant emission in Zn_1-xMn_xS (with x=0.2 and 0.3) and MnS as the energy of exciting radiation is tuned across the Mn and S L_3,2 absorption edge, along with the resonant excited spectra from elemental Mn as a reference

[en] Multicrystalline silicon is a very interesting material for terrestrial solar cells. Its low cost and respectable energy conversion efficiency (12-15%) makes it arguably the most cost competitive material for large-volume solar power generation. However, the solar cell efficiency of this material is severely degraded by regions of high minority carrier recombination which have been shown to possess both dislocations and microdefects. These structural defects are known to increase in recombination activity with transition metal decoration. Therefore, gettering of metal impurities from the material would be expected to greatly enhance solar cell performance. Contrary to this rationale, experiments using frontside phosphorus and/or backside aluminum treatments have been found to improve regions with low recombination activity while having little or no effect on the high recombination regions and in turn only slightly improving the overall cell performance. The goal of this research is to determine the mechanism by which gettering is ineffectual on these high recombination regions. The authors have performed studies on integrated circuit (IC) quality single crystal and multicrystalline solar cell silicon (mc-silicon) in the as-grown state and after a variety of processing/gettering steps. With Surface Photovoltage measurements of the minority carrier diffusion length which is inversely proportional to carrier recombination, they have seen that aluminum gettering is effective for improving IC quality material but ineffective for improving the regions of initially low diffusion lengths (high recombination rates) in mc-silicon. Of particular interest is the great increase in diffusion length for IC material as compared to the mc-silicon. Clearly the IC material has benefited to a greater extent from the gettering procedure than the mc-silicon

No abstract available

[en] Evaluation of f parameter (oscillation force) defining the probability of optic transition and possibility of using the material in electro- and photochromium systems is conducted for two-layer amorphous WO₃ - MoO₃ films. New methods allowing one to determine the ratio of oscillation force values for colour centers in WO₃ and MoO₃ films, are proposed. 9 refs., 3 figs

[en] Magnetization processes in soft ferromagnetic materials consist of complex domain wall movements and domain structure transitions. A micromagnetic model is developed to numerically simulate such dynamic behaviors in order to achieve fundamental understanding of the switching mechanisms involved in magnetic recording sensors, such as thin film inductive heads and magnetoresistive heads. Various energy minimization schemes have been utilized to study the quasi-static equilibrium properties of these micro-structures, whereas the phenomenological Landau-Lifshitz equation is solved to follow the dynamic magnetization response to external driving fields. It is observed that the intrinsic gyromagnetic damping effect introduces dissipation loss in domain wall motion, and induces dynamic transitions of all structures at high amplitude and frequency driving fields. The dynamics of the flux-closure asymmetric vortex wall in permalloy thin films with thicknesses ranging from 500 angstrom to several microns has been studied in detail. The effectiveness of eddy current damping on thick film wall motions is discussed within the micromagnetic context. The magnetic reversals of very thin permalloy platelets have also been investigated. The interactions of magnetostatic and exchange effects introduce formations of transient vortices and multi-domain states for these small (micron-scale) devices, which in turn act as the sources of hysteretic and noisy response to external fields

[en] We investigate the validity of the Fourier transformations that have long been used to transform a given Hamiltonian written in configuration space into momentum space. We show that although these transformations are valid for ideal (perfect) lattices, their use for lattices with vacancies poses mathematical problems and renders inaccuracies in the form of the Hamiltonian by not conserving the number of degrees of freedom in the Hilbert space. Consequently, transformations that avoid this problem are found. We also investigate another solution to this problem that was proposed in the literature. We study the difference between these three methods by investigating the ground-state energy of an electron system in the context of the s-band tight-binding model due to removing (a) one site and (b) two sites. The three methods give similar expressions for the ground-state energy for both of these cases, but they predict different binding energies of electrons at the vacancies

[en] The characteristics of energy transfer and migration processes important in the optical dynamics of Tm,Ho:YAG and Tm:YAG laser crystals were investigated using both time-resolved fluorescence spectroscopy and laser-induced grating spectroscopy. Four-wave mixing techniques were used to produce permanent laser-induced refractive index gratings in Eu-doped silicate glasses. The effects on the characteristics of these permanent gratings produced by changing the divalent modifier ions of the glass host are reported. Efficient long-range energy migration was found to take place in the ³F₄ level of the Tm ions, which enhances the energy transfer to Ho ions. The parameters describing excitation migration were determined experimentally and used to calculate an overall Tm-Ho energy transfer rate. This was found to be in close agreement with the rate determined by the results of fluorescence spectral dynamics measurements. Theoretical estimates were made of the fundamental ion-ion interaction rates responsible for each of the physical processes investigated here and the results were all found to be in close agreement with the experimentally determined values. The author extends previous investigations on the Eu-doped silicate glasses by describing the variation of the four-wave-mixing signal intensity of a series of glasses with different divalent alkaline network modifier ions. The temperature dependence of the signal from one of the samples was measured and a theoretical explanation for the change in the refractive index associated with the double-minimum potential well model is developed

[en] Recent experiments to measure electrical conductivities and temperatures of liquid hydrogen shock-compressed up to Mbar pressures are described and contrasted with results for liquid nitrogen. Some thoughts about future possibilities for high-pressure shock experiments are discussed. copyright 1994 American Institute of Physics

[en] Incoherent exciton dynamics in one-dimensional perfect lattices with traps at sites arranged according to aperiodic deterministic sequences is studied. We focus our attention on Thue-Morse and Fibonacci systems as canonical examples of self-similar aperiodic systems. Solving numerically the corresponding master equation we evaluate the survival probability and the mean-square displacement of an exciton initially created at a single site. Results are compared to systems of the same size with the same concentration of traps randomly as well as periodically distributed over the whole lattice. Excitons progressively extend over the lattice on increasing time and, in this sense, they act as a probe of the particular arrangements of traps in each system considered. The analysis of the characteristic features of their time decay indicates that exciton dynamics in self-similar aperiodic arrangements of traps is quite close to that observed in periodic ones, but differs significantly from that corresponding to random lattices. We also report on characteristic features of exciton motion suggesting that Fibonacci and Thue-Morse orderings might be clearly observed by appropriate experimental measurements. In the conclusions we comment on the implications of our work on the way towards a unified theory of the ordering of matter