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

Topologically guided tuning of Zr-MOF pore structures for highly selective separation of C6 alkane isomers

As an alternative technology to energy intensive distillations, adsorptive separation by porous solids offers lower energy cost and higher efficiency. Herein we report a topology-directed design and synthesis of a series of Zr-based metal-organic frameworks with optimized pore structure for efficient separation of C6 alkane isomers, a critical step in the petroleum refining process to produce gasoline with high octane rating. Zr6O4(OH)4(bptc)3 adsorbs a large amount of n-hexane but excluding branched isomers. The n-hexane uptake is ~70% higher than that of a benchmark adsorbent, zeolite-5A. A derivative structure, Zr6O4(OH)8(H2O)4(abtc)2, is capable of discriminating all three C6 isomers and yielding a high separation factor for 3-methylpentane over 2,3-dimethylbutane. This property is critical for producing gasoline with further improved quality. Multicomponent breakthrough experiments provide a quantitative measure of the capability of these materials for separation of C6 alkane isomers. A detailed structural analysis reveals the unique topology, connectivity and relationship of these compounds

Alkylation of Silicon(111) surfaces

Methylation of chlorine-terminated silicon (111) (Si-Cl) is investigated by Infra Red Absorption Spectroscopy (IRAS). Starting from an atomically flat H-terminated Si(111), the surface is first chlorinated by a gas phase process, then methylated using a Grignard reagent. Methyl groups completely replace Cl, and are oriented normal to the surface. The surface remains atomically flat with no evidence of etching

Applications of Infrared Absorption Spectroscopy to the Microelectronic Industry

Silicon oxide and hydrogen are ubiquitous in materials and processing issues in microelectronics. This paper reviews the value of infrared absorption spectroscopy to characterize the chemical and structural nature of silicon oxides, including buried oxides, and the presence of hydrogen both at silicon surfaces and in silicon oxides. Results involving the wet chemical cleaning of silicon and the fabrication issues of Silicon-on-Insulator are presented. Particular emphasis is given to the characterization of buried interfaces, for which IR spectroscopy is particularly useful.L'oxyde de silicium et l'hydrogène jouent un rôle important dans la fabrication de matériaux pour les composants microélectroniques. Cet article présente la spectroscopie infrarouge comme une technique de grande valeur pour caractériser chimiquement et structurellement l'oxyde de silicium, tant en surface qu'enfoui, et pour detecter la présence d'hydrogène aux surfaces et dans l'oxyde de silicium. Les résultats présentés comprennent le décapage en solutions chimiques et les problèmes de fabrication de matériau Silicium-sur-Isolant. Cette présentation est centrée en particulier sur la caractérisation des interfaces internes, pour lesquelles la spectroscopie infrarouge est particulièrement utile

IR SPECTROSCOPY WITH SURFACE ELECTROMAGNETIC WAVES

On utilise des ondes électromagnétiques de surface pour tester les modes de vibration de molécules sur des surfaces métalliques.Surface electromagnetic waves are used to probe molecular vibrational modes on metal surfaces

Adsorption states and orientation of N-alkyl anhydride molecules on oxidized aluminium surface

International audienc

Colored porous silicon as support for plasmonic nanoparticles

Colored porous silicon as support for plasmonic nanoparticles M. Lublow,1,2,a S. Kubala,1,2 J. F. Veyan,3 and Y. J. Chabal3 1Helmholtz Centre Berlin for Materials and Energy, Institute for Heterogeneous Materials Systems, Berlin, Germany 2Department of Physical Chemistry, Fritz Haber Institute, Berlin, Germany 3Department of Materials Science and Engineering, University of Texas at Dallas, Texas, USA Received 15 November 2011; accepted 9 March 2012; published online 16 April 2012 Colored nanoporous silicon thin films were employed as dielectric spacing layers for the enhancement of localized surface plasmon LSP polaritons. Upon formation of Au nanoparticles Au NPs on these layers, a visible color change is observed due to multiple LSP resonance excitations. Far field effects were assessed by angle resolved reflectometry. Resonance enhancements, particularly for s polarized light, account for the observed color change and are discussed in terms of effective medium and Mie scattering theory. Enhancements of the electric field strengths in the near field and of the absorption in the substrate were deduced from finite difference time domain calculations and exceed considerably those of the non porous Au NP Si interface. First results of improved photoelectrocatalytic hydrogen evolution at these interfaces are discussed. Samples were prepared by varied procedures of metal assisted etching and dry etching with XeF2. Structural and chemical properties were investigated by scanning electron and atomic force microscopy as well as energy dispersive x ray analysis. VC 2012 American Institute of Physics. [http dx.doi.org 10.1063 1.370346