Metal silicon interactions: the electronic structure of transition metal silicides as a basis for metal silicon interface studies

Contains fulltext : mmubn000001_116775297.pdf (publisher's version ) (Open Access)Promotor : J. Fuggle125 p

Motor Unit Territories and Fiber Types in Rabbit Masseter Muscle

The myosin heavy chain (MHC) content and spatial distribution of the fibers of 11 motor units (MUs) of the rabbit masseter muscle were determined. The fibers of single MUs were visualized in whole-muscle serial sections by a negative periodic acid/Schiff reaction for glycogen after they had been depleted of glycogen by extracellular stimulation of their motoneuron in the trigeminal motor nucleus. The MHC isoforms present in the fibers were characterized by monoclonal antibodies. Individual fibers appeared to contain from one to three MHC isoforms. In six cases, all fibers of a motor unit had an identical MHC content; in five cases, different fiber types were found in a single unit. The fiber number per MU varied between 40 and 424, the territory size between 1.1 and 11.0 mm2 (of a total muscle cross-section of 200 mm2), and fiber density between 6 and 17 MU fibers per 100 muscle fibers. In the multipennate masseter, the fibers were usually restricted to a single anatomical compartment. In comparison with leg muscles, the fibers of the masseter motor units, although similar in number, were restricted to relatively smaller subvolumes of the muscle and thus reached higher densities in their territories. The small territories are the anatomical substrate for the observed heterogeneity of motor behavior. Since the different anatomical compartments of the masseter differ with respect to their biomechanical capabilities, this makes this muscle multifunctional in the exertion of complex motor tasks

HIGH ENERGY SPECTROSCOPIES OF Cu COMPOUNDS, INCLUDING THE NEW SUPERCONDUCTORS

High energy spectroscopies are well suited to address the controversial issue of Cu valence in the new high Tc superconductors, as they can discriminate between various possible Cu configurations (d8, d9 or d10). XAS, XPS and AES spectra of CuI, CuII and CuIII compounds show that, as a results of hybridization, the actual Cu d-count can be quite different from what is expected from simple considerations based on the formal valence. A value of ~ 9.3. is inferred electrons for the superconducters. Discrepancies in the published results are attributed to insufficient sample characterization : we propose to adopt the O is XPS signal as a standard probe of surface condition in these materials

X-ray-emission studies of chemical bonding in transition-metal silicides

We present Si L2,3 emission-band spectra of a series of 3d and 4d transition-metal (TM) silicides, together wtih Si K emission-band spectra of four 3d TM disilicides. The data are compared with augmented-spherical-wave density-of-states (DOS) calculations, and good agreement is found. The trends we find are explained with a general scheme for chemical bonding in TM silicides. The differences between the experimental data and the calculated DOS curves are tentatively attributed to self-energy effects.

Core-hole effects in the x-ray-absorption spectra of transition-metal silicides

We report systematic differences between the shape of the Si K x-ray-absorption spectra of transition-metal silicides and broadened partial densities of Si p states. We use a variety of calculations to show that the origin of these discrepancies is the core-hole potential appropriate to the final state. The effects can be successfully described by ab initio supercell calculations which explicitly include the presence of the hole in the excited state. A Clogston-Wolff model, with the ground-state partial densities of states at the site to be ionized as input data, can also describe the core-hole effect and is found to be a useful tool for the understanding of core-hole effects.

X-ray Emission and Absorption Studies of Silicides in Relation to their Electronic Structure

The valence bands and conduction bands of about 30 transition metal silicides (of which we concentrate on 4 here) have been investigated by measurements of Si X-ray emission bandsspectra, X-ray absorption spectra near the Si K (1s) edge, photoemission spectra, and Bremsstrahlung Isochromat spectra. The densities of states have also been calculated for the materials in their real crystal structures. The influence of the core hole on some spectra has been investigated using supercell calculations, a (Greens function) generalized Clogston-Wolff model, and Auger spectroscopy. A selection of results is presented to illustrate the utility of site and selective methods in investigations of the electronic structure of silicides and the nature of the "quasi-gap" of the partial density of Si p states in the region of the transition metal d bands.