Contribution of the Internal Field to the Anisotropic Optical Reflectance of GaP(110)

This article presents the theory of optical reflection from thin slabs of GaP(110) by means of the discrete dipole model and focusses especially upon the possible implications of this model for the surface induced optical anisotropy. The reflectance of a semi-infinite sample is extracted from slab calculations and compared with experiments. We find that the internal field has a very important role in determining the surface induced optical anisotropy. We also show that the surface sensitivity of such experiments can be estimated to be about five monolayer

Ab initio study of reflectance anisotropy spectra of a sub-monolayer oxidized Si(100) surface

The effects of oxygen adsorption on the reflectance anisotropy spectrum (RAS) of reconstructed Si(100):O surfaces at sub-monolayer coverage (first stages of oxidation) have been studied by an ab initio DFT-LDA scheme within a plane-wave, norm-conserving pseudopotential approach. Dangling bonds and the main features of the characteristic RAS of the clean Si(100) surface are mostly preserved after oxidation of 50% of the surface dimers, with some visible changes: a small red shift of the first peak, and the appearance of a distinct spectral structure at about 1.5 eV. The electronic transitions involved in the latter have been analyzed through state-by-state and layer-by-layer decompositions of the RAS. We suggest that new interplay between present theoretical results and reflectance anisotropy spectroscopy experiments could lead to further clarification of structural and kinetic details of the Si(100) oxidation process in the sub-monolayer range.Comment: 21 pages, 8 figures. To be published in Physical Rev.

Role of surface structural motifs on the stability and reflectance anisotropy spectra of Sb-rich GaSb(001) reconstructions

The structure of the technologically important-but still mostly unknown-GaSb(001)-c(2 x 6) surface reconstruction is investigated by means of ab initio simulations of reflectance anisotropy spectroscopy (RAS) and total energy calculations. A large number of reconstruction models for the GaSb(001) surface in the Sb-rich coverage regime are considered. The influence of each single surface structural motif on the RAS spectra is studied in detail, as well as their role in the surface stability with regard to application of the electron counting rule (ECR). We interpret the features of the RAS data measured for this reconstruction and suggest a new model for the c(2 x 6) phase. In this model a few Sb atoms in the second layer are randomly substituted by Ga, forming surface antisite defects. When used to fulfill the ECR, this "doping" effect considerably lowers the total energy of the long chain c(2 x 6) reconstruction model, making it competitive with the more stable short-chain (4 x 3) reconstructions. Formation of the surface antisites occurs spontaneously in the presence of dynamical negative charge fluctuations and is favored by the excellent matching between GaSb(001) and metallic Sb and by the natural softness of the Ga-Sb bonds. Calculations of the reflectance anisotropy spectra confirm that this structure is a major component of a largely disordered surface, where motifs of the stable (4 x 3) reconstructions are also present

Test of long-range exchange-correlation kernels of time-dependent density functional theory at surfaces: Application to Si(111)2×1

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Quasiparticle Electronic structure of Copper in the GW approximation

We show that the results of photoemission and inverse photoemission experiments on bulk copper can be quantitatively described within band-structure theory, with no evidence of effects beyond the single-quasiparticle approximation. The well known discrepancies between the experimental bandstructure and the Kohn-Sham eigenvalues of Density Functional Theory are almost completely corrected by self-energy effects. Exchange-correlation contributions to the self-energy arising from 3s and 3p core levels are shown to be crucial.Comment: 4 pages, 2 figures embedded in the text. 3 footnotes modified and 1 reference added. Small modifications also in the text. Accepted for publication in PR

Advances in Nanomaterials Based on Cashew Nut Shell Liquid

Cashew nut shell liquid (CNSL), obtained as a byproduct of the cashew industry, represents an important natural source of phenolic compounds, with important environmental benefits due to the large availability and low cost of the unique renewable starting material, that can be used as an alternative to synthetic substances in many industrial applications. The peculiarity of the functional groups of CNSL components, such as phenolic hydroxyl, the aromatic ring, acid functionality, and unsaturation(s) in the C15 alkyl side chain, permitted the design of interesting nanostructures. Cardanol (CA), anacardic acid (AA), and cardol (CD), opportunely isolated from CNSL, served as building blocks for generating an amazing class of nanomaterials with chemical, physical, and morphological properties that can be tuned in view of their applications, particularly focused on their bioactive properties

Ab initio optical properties of Si(100)

We compute the linear optical properties of different reconstructions of the clean and hydrogenated Si(100) surface within DFT-LDA, using norm-conserving pseudopotentials. The equilibrium atomic geometries of the surfaces, determined from self-consistent total energy calculations within the Car-Parrinello scheme, strongly influence Reflectance Anisotropy Spectra (RAS), showing differences between the p(2x2) and c(4x2)reconstructions. The Differential Reflectivity spectrum for the c(4x2) reconstruction shows a positive peak at energies < 1 eV, in agreement with experimental results.Comment: fig. 2 correcte

Strong excitons in novel two-dimensional crystals: Silicane and germanane

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Reflectivity Anisotropy Spectra of Cu- and Ag- (110) surfaces from {\it ab initio} theory

We are able to disentagle the effects of the intraband and interband parts of the bulk dielectric function on the bare dielectric anisotropy of the surface. We show how the position, sign and amplitude of the structures observed in such spectra depend on the above quantities. The lineshape of all the calculated structures agree very well with the ones observed experimentally for samples treated by suitable surface cleaning. In particular, we reproduce the observed single peak structure of Ag at high energy, found to represent a state of the clean surface different from the one giving the originally observed double peak structure. This results is not reproduced by the 'local field' model.Comment: 4 pages, 3 figures. submitted to Phys. Rev. Let