Showing papers by "Mahesh G. Samant published in 1996"

NEXAFS Studies on the Surface Orientation of Buffed Polyimides

Abstract: Near-edge X-ray absorption fine structure (NEXAFS) spectroscopy has been used to determine the average near-surface orientation of chains in a buffed polyimide film Auger and total electron yield measurements provide powerful and direct means of determining the orientation of chains as a function of depth In the case of a strongly buffed sample, the polyimide chains at the film surface are found to be highly aligned along the buffing direction We also find significant alignment of the phenyl ring planes parallel to the surface The alignment is discussed in terms of simple models that are useful in visualizing the alignment in partially disordered systems The chain orientation decays as a function of distance from the surface, becoming random in the bulk The 1/e alignment depth is ≃100 A Studies as a function of load applied during buffing and distance of buffing show that the near-surface orientation saturates at relatively small loads and short distances The 1/e buffing load and buffing distance

One-step and two-step description of deexcitation processes in weakly interacting systems.

Abstract: The origin of one- and two-step behavior of core-hole decay processes is identified in connection with high resolution autoionization spectra for Ar/Pt(111). The spectra simultaneously show feature ...

L-edge x-ray absorption in fcc and bcc Cu metal: Comparison of experimental and first-principles theoretical results

Abstract: High resolution Cu ${\mathit{L}}_{2,3}$ x-ray absorption spectra of bulk fcc Cu metal are compared with those of thin Cu layers in Cu/Fe multilayers. Comparison of the measured fine structure with that obtained from a fully relativistic first-principles calculation for fcc and bcc Cu reveals that Cu is bcc in Cu(3 \AA{})/Fe(10 \AA{}) and fcc in Cu(10 \AA{})/Fe(3 \AA{}) multilayers. This result indicates that the thicker layer simply acts as a template for the structure of the thinner layer. The excellent agreement between experimental and theoretical spectra also demonstrates the validity of the theoretical approach. The theoretical spectra are discussed in terms of their angular momentum composition and the energy dependence of the radial transition matrix elements. \textcopyright{} 1996 The American Physical Society.

Determination of the electronic density of states near buried interfaces: Application to Co/Cu multilayers

Abstract: High-resolution ${\mathit{L}}_{3}$ x-ray absorption and emission spectra of Co and Cu in Co/Cu multilayers are shown to provide unique information on the occupied and unoccupied density of d states near buried interfaces. The d bands of both Co and Cu interfacial layers are shown to be considerably narrowed relative to the bulk metals, and for Cu interface layers the d density of states is found to be enhanced near the Fermi level. The experimental results are confirmed by self-consistent electronic structure calculations. \textcopyright{} 1996 The American Physical Society.

Applications of soft x-ray fluorescence spectroscopy in materials science

Abstract: Soft x-ray fluorescence spectroscopy provides an element and angular momentum selective measure of the valence band density of states in complex materials. Results are presented demonstrating the use of SXF both as a means of solving materials problems and as a means of increasing the fundamental understanding of low energy excitation processes in various types of materials. As examples of materials applications, the authors discuss the L spectra of Si in various environments, and describe radiation damage studies in Beryl. Fundamental new insights are provided by the study of SXF spectra excited near an x-ray threshold. For such excitation, recent work demonstrates that an electronic Raman scattering process can greatly modify the normal fluorescence spectrum. The authors discuss near threshold studies of graphite, h-BN and NiS to demonstrate that the nature of the electronic excitation processes differs dramatically in various classes of materials and provides important new insights into their properties.

Surface Physics with Synchrotron Radiation

Abstract: This article illustrates the use of synchrotron radiation for illuminating the electronic structure of surfaces. After a brief introduction into the most common spectroscopies, their capabilities are exposed by a set of examples from the authors’ area of expertise. It comprises the surface and interface chemistry of semiconductors and magnetic materials, but leaves out a large body of work on surface chemistry of heterogeneous catalysis.