Peer-reviewed Publications |
Enriquez, H., Vizzini, S., Kara, A., Lalmi, B., & Oughaddou, H. (2012). Silicene structures on silver surfaces. JOURNAL OF PHYSICS-CONDENSED MATTER, 24(31), 314211.
Résumé: In this paper we report on several structures of silicene, the analog of graphene for silicon, on the silver surfaces Ag(100), Ag(110) and Ag(111). Deposition of Si produces honeycomb structures on these surfaces. In particular, we present an extensive theoretical study of silicene on Ag(111) for which several recent experimental studies have been published. Different silicene structures were obtained only by varying the silicon coverage and/or its atomic arrangement. All the structures studied show that silicene is buckled, with a Si-Si nearest neighbor distance varying between 2.28 and 2.5 angstrom. Due to the buckling in the silicene sheet, the apparent (lateral) Si-Si distance can be as low as 1.89 angstrom. We also found that for a given coverage and symmetry, one may observe different scanning tunneling microscopy images corresponding to structures that differ by only a translation.
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Kara, A., Enriquez, H., Seitsonen, A. P., Voon, L. C. L. Y., Vizzini, S., Aufray, B., & Oughaddou, H. (2012). A review on silicene-New candidate for electronics (vol 67, pg 1, 2012). SURFACE SCIENCE REPORTS, 67(5), 1–18.
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Labidi, H., Kantorovich, L., & Riedel, D. (2012). Atomic-scale control of hydrogen bonding on a bare Si(100)-2x1 surface. PHYSICAL REVIEW B, 86(16), 165441.
Résumé: The control of the dissociative adsorption of individual hydrogen molecules is performed on the silicon surface at the atomic scale. It is achieved using the tip of a low-temperature (9 K) scanning tunneling microscope (STM) exposed to 10(-6) torr of H-2 and by probing the bare Si(100)-2 x 1 surface at a positive bias. This effect is very localized and is induced by the tunnel electrons. The statistical study of this process reveals an activation energy threshold matching the creation of H-2(-) at the surface of the STM tip. Our results are supported by ab inito density functional calculations of a hydrogenated silicon dimer.
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Raseev, G. (2012). Laser fields at flat interfaces: I. Vector potential. Eur. Phys. J. D, 66(7), 179.
Résumé: A model calculating the laser fields at a flat structureless surface taking into account the surface photoelectric effect is presented. The photon is p or transverse magnetic linearly polarized, continuous and its wave length is long, i.e. lambda(vac) >= 12.4 nm. The sharp rise of the electron density at the interface generates an atomic scale spatial dependence of the laser field. In real space and in the temporal gauge, the vector potential A of the laser is obtained as a solution of the classical Ampere-Maxwell and the material equations. The susceptibility is a product of the electron density of the material system with the surface and of the bulk tensor and non-local isotropic (TNLI) polarizability. The electron density is obtained quantum mechanically by solving the Schrodinger equation. The bulk TNLI polarizability including dispersion is calculated from a Drude-Lindhard-Kliewer model. In one dimension perpendicular to the surface the components A(x)(z,omega) and A(z)(z,omega) of the vector potential are solutions of the Ampere-Maxwell system of two coupled integro-differential equations. The model, called vector potential from the electron density-coupled integro-differential equations (VPED-CIDE), is used here to obtain the electron escape probability from the power density absorption, the reflectance, the electron density induced by the laser and Feibelman's parameters d(parallel to) and d(perpendicular to). Some preliminary results on aluminium surfaces are given here and in a companion paper the photoelectron spectra are calculated with results in agreement with the experiment.
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Raseev, G. (2012). Laser fields at flat interfaces: II. Plasmon resonances in aluminium photoelectron spectra. Eur. Phys. J. D, 66(7), 180.
Résumé: Using the model derived in paper I [G. Raseev, Eur. Phys. J. D 66, 167 (2012)], this work presents calculations of the photoelectron spectrum (PES) of low index aluminium surfaces in the 10-30 eV region. The laser is p or transverse magnetic linearly polarized incident on a flat structureless surface and its fields are modeled in I using the vector potential in the temporal gauge. This model uses a tensor and nonlocal isotropic (TNLI) susceptibility and solves the classical Ampere-Maxwell equation through the use of the vector potential from the electron density-coupled integro-differential equations (VPED-CIDE). The PE cross sections are the squares of the PE transition moments calculated using the VPED-CIDE vector potential function of the penetration coordinate. The PES is obtained in a one step model using either the Fermi golden rule or the Weisskopf-Wigner (WW) expressions. The WW cross section PES compares favorably with the experimental angle and energy resolved photoelectron yield (AERPY) spectrum of Levinson et al. [Phys. Rev. Lett. 43, 952 (1979)], Levinson and Plummer [Phys. Rev. B 24, 628 (1981)] for Al(001) and of Barman et al. [Phys. Rev. B 58, R4285 (1998)], Barman [Curr. Sci. 88, 54 (2005)] for Al(111) surfaces. As in the experiment, our theoretical AERPY displays the multipole surface plasmon resonance at 11.32/12.75 eV for Al(001)/Al(111), mainly due to the surface contribution vertical bar <psi(f)vertical bar p . A vertical bar psi(i)>vertical bar(2), the bulk plasmon minimum at 15 eV and the two single particle excitation resonances at about 16 and 22 eV. The nature of the plasmon resonances of the PES is analyzed using the reflectance, the electron density induced by the laser and Feibelman's parameter d(perpendicular to) all introduced in paper I.
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