ELECTRONIC-STRUCTURE OF AMORPHOUS SI-N COMPOUNDS

We have measured valence-band photoemission spectra and dark conductivity of a-SiN(x):H compounds for compositions between x = 0 and x = 1.35. The photoemission spectra have been measured with Zr Mzeta and Al Kalpha radiation of 151.4 and 1486.6 eV, respectively. At hnu = 151.4 eV the spectra resemble directly the total density-of-states (DOS) of the system; the most important change with x is the shift of spectral weight from near the valence-band maximum (VBM) toward the center of the band, indicating the change from a band of Si-Si bonding states to a band of Si-N bonding states. At hnu = 1486.6 eV the spectra are dominated by the contribution of the Si-3s partial DOS; this contribution is located at the bottom of the band and shifts toward higher binding energies with increasing x. We compare our results at x = 0.36 and x = 1.35 with those of two recent calculations. Combining results of the dark-conductivity measurements and the photoemission spectra with a previous determination of the optical gaps we make a plot of the VBM, Fermi-level position, and conduction-band minimum (CBM) versus x. It is shown that the sudden opening of the gap at x approximately 1 is due mainly to the recession of the CBM.4919134461345

Modelling collective cell behaviour

The classical mean-field approach to modelling biological systems makes a number of simplifying assumptions which typically lead to coupled systems of reaction-diffusion partial differential equations. While these models have been very useful in allowing us to gain important insights into the behaviour of many biological systems, recent experimental advances in our ability to track and quantify cell behaviour now allow us to build more realistic models which relax some of the assumptions previously made. This brief review aims to illustrate the type of models obtained using this approach

BOND DENSITIES AND ELECTRONIC-STRUCTURE OF AMORPHOUS SINX-H

4295677568

Bond Densities And Electronic Structure Of Amorphous Sinx:h

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)We present a study of amorphous hydrogenated silicon-nitrogen alloys (a-SiNx:H, 0 x1, Si-N bonds increase at the expense of both Si-Si and Si-H bonds; however, this is not enough to saturate the three N valencies with Si and some N-H and possibly N-N bonds begin to appear. The opening of the optical gap occurs at x 1.1 when the ratio of the densities of Si-Si bonds to Si-N bonds has fallen below 0.10. Near stoichiometry, substantial amounts of Si-Si and N-H bonds are observed. The possibility of segregation into pure silicon and stoichiometric silicon nitride is discussed by analyzing the Si 2p line shape. A linear relationship between the Si 2p chemical shift and the mean number of N-atom nearest neighbors of Si is observed; a charge transfer of 0.35e per Si-N bond is determined. © 1990 The American Physical Society.42956775684CAPES; Conselho Nacional de Desenvolvimento Científico e Tecnológico; CNPq; Conselho Nacional de Desenvolvimento Científico e Tecnológico; FAPESP; Conselho Nacional de Desenvolvimento Científico e TecnológicoFundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP

Building two-dimensional metal-organic networks with tin

We show that Sn atoms combined with organic ligands can be used to build 2D coordination networks on Au(111) surfaces

Stabilization of high-spin Mn ions in tetra-pyrrolic configuration on copper

By means of Mn-Cu transmetalation, we incorporated Mn atoms in an array of TCNQ (7,7,8,8-tetracyanoquinodimethane) grown on Cu(100), forming a long range ordered and commensurate metal\u2013organic coordination network (MOCN). Preliminary Sn alloying of the Cu(100) surface allowed us to control the degree of substrate reactivity, thus preventing the chemical interaction of the Mn-TCNQ MOCN with the substrate. Mn2+ ions are stabilized in an artificial tetra-pyrrolic coordination, which mimics the macrocyle configuration of Mn-phthalocyanines/porphyrins. X-ray absorption spectroscopy at the Mn L2,3-edge indicates that the Mn ions are in a high-spin state (S = 5/2), in agreement with DFT + U calculations which also shows that the electronic structure of this Mn-TCNQ MOCN is very similar to that of the corresponding unsupported MOCN