Publications

2002

• Semi-empirical and ab initio calculations of the optical properties of semiconductor superlattices
  
  • Botti Silvana
  , 2002. The birefringence of GaAs/oxidized AlAs superlattice has recently provided interesting applications to non-linear optics laser devices. GaAs/vacuum superlattices are a possible model for multilayers formed by GaAs and a wide-gap oxide. They are not only a model system, in fact free standing GaAs films can be produced. First, we have calculated the electronic states and the optical properties of GaAs/AlAs and GaAs/vacuum superlattices within a semi-empirical pseudopotential framework. The features in the optical spectra are well reproduced and the peak positions agree with experiments. Nevertheless, the optical anisotropy cannot be correctly described without the inclusion of local field effects. Thus, we have performed {\it ab initio} calculations of the birefringence, within the Time Dependent Density Functional Theory (TDDFT). Neglecting local field effects, we confirm the results of semi-empirical calculations. When local field effects are included agreement with experiments can be obtained.
• Synthesis of nanometric cubic BaTiO3 by using and original chemical route: Freeze-drying method
  
  • Bogicevic Christine
  • Laher-Lacour F.
  • Malibert C.
  • Dkhil B.
  • Menoret C.
  • Dammak H.
  • Giorgi Marie-Laurence
  • Kiat Jean-Michel
  Ferroelectrics, Taylor & Francis: STM, Behavioural Science and Public Health Titles, 2002, 270 (1), pp.57-62. (10.1080/00150190211234)
  DOI : 10.1080/00150190211234
• ω phase individual latent tracks induced by irradiation of α-titanium with megaelectronvolt fullerenes
  
  • Angiolini M.
  • Dammak Hichem
  • Dunlop A.
  Philosophical Magazine Letters, Taylor & Francis, 2002, 82 (2), pp.81-89. Evidence is obtained for the existence of a hexagonal ω phase in individual latent tracks (i.e. in the vicinity of the ion paths) induced in hcp α-Ti after irradiation at 80 K at low fluences with 30 MeV C60 ions. The orientation relationships between the α and ω phases are those previously observed by Dammak et al. in 1993 when the ω phase is obtained after irradiation at high fluences with gigaelectronvolt monomers at low temperatures (i.e. (002)α∥(21̄0)ω and [100]α∥[001]ω). Parallel moiré fringes, due to the overlapping of the structure of the ω phase with the α matrix, are observed in bright-field images obtained with (020)α(∥(030)ω) reflection conditions. The spacing of these fringes is very close to the value of 3.2 nm expected from the interplanar distances d(020)α and d(030)ω. After irradiation at 300 K, such fringes are also observed but the track structure cannot be established unambiguously. This dependence of the irradiation temperature is related to the temperature-pressure structural properties. The present transmission electron microscopy observations are compared with those obtained by Dammak et al. in 1996 and 1999 in the case of irradiation with gigaelectronvolt monomers for which it has been established that an overlapping of tracks is necessary to induce the α → ω transformation. (10.1080/09500830110100679)
  DOI : 10.1080/09500830110100679
• OPTICS OF INSTANTANEOUS WAVES
  
  • Shvartsburg Alexandr B.
  • Petite Guillaume
  , 2002, pp.143-214. This review is devoted to the transient optical phenomena, displayed both in the spatiotemporal dynamics of ultrashort single - cycle wave pulses in free space and dispersive dielectrics as well as to interaction of light with non-stationary media. The interplay of diffractive and dispersive phenomena, including the coupled processes of amplitude and phase reshaping, spectral variations, polarity reversal for different types of light pulses, is examined in frequency and time domains. Reflection - refraction effects on the interfaces of media with time-dependent dielectric susceptibility are considered by means of exact analytical solutions of Maxwell equations for these media. The non - stationarity - induced dispersion is shown to provide a dynamical regime of reflectivity of non-stationary media, depending upon both instantaneous dielectric susceptibility and its temporal derivative; the relevant generalization of Fresnel formulae is presented
• Ab Initio Calculations of the Anisotropic Dielectric Tensor of GaAs/AlAs Superlattices
  
  • Botti Silvana
  • Vast N.
  • Reining L.
  • Olevano Valério
  • Andreani L.C.
  Physical Review Letters, American Physical Society, 2002, 89, pp.216803. The static dielectric properties of (001)(GaAs)p/(AlAs)p superlattices have been calculated as a function of their period p for 1≤p≤12, starting from density-functional theory. The interplay between quantum confinement and local field effects is shown to be crucial. For light polarized in the growth direction it leads to the otherwise surprising justification of the use of a classical effective medium theory, even for the smallest periods. Only the inclusion of both contributions allows in ab initio and in semiempirical calculations to reproduce the experimentally observed birefringence. (10.1103/PhysRevLett.89.216803)
  DOI : 10.1103/PhysRevLett.89.216803
• A new class of low compressibility materials : clathrates of silicon and related materials
  
  • San Miguel Alfonso
  • Mélinon Patrice
  • Blase Xavier
  • Tournus Florent
  • Connetable Damien
  • Reny Edouard
  • Yamanaka S.
  • Itié Jean-Paul
  • Cros Christian
  • Pouchard Michel
  High Pressure Research, Taylor & Francis, 2002, 22 (3-4), pp.539-544. We discuss the high pressure properties of different silicon clathrate structures that we have investigated by means of X-ray diffraction and ab initio calculations. Compressibility, transition pressures or phase transformations are interpreted as a function of the nature of the guest atom intercalation. The compressibility of the clathrate structure is in all cases close to that of silicon diamond whereas transition pressures or the high pressure phases are extremely depending on the nature of the guest atom. We address the implications for obtaining a metallic material as hard as diamond. (10.1080/08957950212454)
  DOI : 10.1080/08957950212454
• Excitonic effects in solids described by time-dependent density functional theory
  
  • Reining Lucia
  • Olevano Valério
  • Rubio Angel
  • Onida Giovanni
  Physical Review Letters, American Physical Society, 2002, 88, pp.066404. Starting from the many-body Bethe-Salpeter equation we derive an exchange-correlation kernel $f_{xc}$ that reproduces excitonic effects in bulk materials within time-dependent density functional theory. The resulting $f_{xc}$ accounts for both self-energy corrections and the electron-hole interaction. It is {\em static}, {\em non-local} and has a long-range Coulomb tail. Taking the example of bulk silicon, we show that the $- \alpha / q^2$ divergency is crucial and can, in the case of continuum excitons, even be sufficient for reproducing the excitonic effects and yielding excellent agreement between the calculated and the experimental absorption spectrum.
• Measuring thermal effects in femtosecond laser-induced breakdown of dielectrics
  
  • Ladieu F
  • Martin Ph
  • Guizard S.
  Applied Physics Letters, American Institute of Physics, 2002. A quartz sample was submitted to femtosecond laser pulses with fluences up to 6×Fc,6×Fc, where FcFc is the laser-induced breakdown fluence. A series of microthermocouples, deposited onto the surface, was used to measureheatings at the millisecond scale, at typically 50 μm from the laser impact. By using both the heat propagation equation and the Helmholtz equation to get the energy absorption profile, we estimate a minimum value of the temperature reached in the center of the crater. Even very close to Fc,Fc, this temperature is found to be ≳3000 °C,≳3000 °C, proving that heating effects play a major role in the breakdown of dielectrics. (10.1063/1.1498147)
  DOI : 10.1063/1.1498147