20 research outputs found
ĂTUDE DE LA RĂPARTITION DES IONS ET DES DĂFAUTS CRĂĂS PAR IMPLANTATION DANS LES SEMI-CONDUCTEURS PAR INTERFĂROMĂTRIE INFRAROUGE
Des interfĂ©rences apparaissent dans les spectres de rĂ©flectivitĂ© infrarouge effectuĂ©s sur des couches Ă©pitaxiĂ©es sur des semi-conducteurs fortement dopĂ©s. Nous avons approfondi l'Ă©tude de ce phĂ©nomĂšne sur des couches prĂ©sentant une interface abrupte (substrats dopĂ©s Ă l'arsenic). Nous avons mis en Ă©vidence des interfĂ©rences dans les spectres de rĂ©flectivitĂ© d'Ă©chantillons implantĂ©s (bore et phosphore ; 1-2 MeV ; recuit Ă 950 °C). Nous avons observĂ© des piĂšges Ă Ă©lectrons crĂ©Ă©s par implantation â avant recuit â sur des Ă©chantillons uniformĂ©ment dopĂ©s (â 1019 e/cm3) et implantĂ©s. Nous concluons que l'interfĂ©romĂ©trie infrarouge est une bonne mĂ©thode pour l'Ă©tude des inhomogĂ©nĂ©itĂ©s superficielles des semi-conducteurs.Interferences appear in infrared reflectivity spectra observed on epitaxial layers on heavily doped semiconductors. We deepened the study of this phenomenon on layers which have a sharp interface (arsenic doped substrates). We observed interferences in the reflectivity spectra of implanted samples (boron and phosphorus ; 1-2 MeV ; annealed at 950 °C). Electron traps created by implantation have been observed â before annealing â on uniformly doped (â 1019 e/cm3) implanted samples. We conclude that the infrared interferometry is a good method for the study of superficial inhomogeneity of semiconductors
ELECTROCHEMICAL OXIDATION AND REDUCTION OF POLYPARAPHENYLENE
Nous avons oxydĂ© et rĂ©duit par Ă©lectrochimie du polyparaphĂ©nylĂšne (P.P.P.) synthĂ©tisĂ© sous forme de poudre (1) Ă partir du benzĂšne. GrĂące Ă la porositĂ© de l'Ă©lectrode de polymĂšre, celui-ci peut ĂȘtre oxydĂ© et rĂ©duit trĂšs facilement malgrĂ© sa grande rĂ©sistivitĂ© initiale. Nous avons observĂ© de forts courants de dĂ©charge, mais une efficacitĂ© coulombique limitĂ©e. La diffĂ©rence entre les potentiels de dĂ©but d'oxydation et de rĂ©duction, de l'ordre de 2,8 V, est plus faible que celle rapportĂ©e jusqu'ici (2).We have studied the electrochemical oxidation and reduction of polyparaphenylene (P.P.P.) synthesized in powder form from benzene (1). Although initially insulating, the polymer could be oxidized or reduced very easily due to a good porosity of the material. High discharge currents could be obtained, but with a limited coulombic efficiency. The difference between the onset voltages of oxidation and reduction is about 2.8 V, that is a lower value than that previously reported (2)
Laser micro-film machine for processing objects having thin films such as integrated circuits
A laser micro-beam machine for processing objects (18) which have thin films, comprising a laser (10) coupled with a microscope (14) and characterized in that the laser (10) is a low average power pulsed laser producing very short pulses. The machine can be used in particular for cutting thermally conductive layers on integrated electronic circuits
Ătude de lâoxydation par AsF
Lâoxydation de couches minces de parasexiphĂ©nyle a Ă©tĂ© suivie par spectromĂ©trie dâabsorption U.V.-visible. Deux nouvelles absorptions centrĂ©es Ă 3 eV et 1,25 eV indiquent la crĂ©ation dâĂ©tats localisĂ©s dans la bande interdite qui rĂ©sultent de lâapparition dâune structure quinoĂŻde. Cette structure est mise en Ă©vidence par diffusion Raman et par absorption I.R., qui de plus montrent bien que lâoxydation du parasexiphĂ©nyle est rĂ©versible sous nos conditions opĂ©ratoires
RAMAN SCATTERING INDUCED BY UNDOPED AND DOPED POLYPARAPHENYLENE
Nous prĂ©sentons les rĂ©sultats de diffusion Raman obtenus sur des Ă©chantillons de polyparaphĂ©nylĂšne prĂ©parĂ©s par deux mĂ©thodes diffĂ©rentes. Les meilleurs spectres sont ceux fournis pour des excitations laser U.V. et les bandes Raman observĂ©es sont Ă 1216 cm-1, 1276 cm-1 et 1598 cm-1 (pour λL = 334,8 nm). Une comparaison avec les spectres Raman induits par les oligomĂšres nous permet de corrĂ©ler l'intensitĂ© de la bande Raman Ă â 1220 cm-l avec le nombre de noyaux phĂ©nyl qui composent le matĂ©riau Ă©tudiĂ©.Raman scattering results on polyparaphenylene samples prepared by two different methods are presented. The best spectra are obtained with an excitation wavelength in the U.V. range and the Raman bands are peaked at 1216 cm-1, 1276 cm-1 and 1598 cm-1 for λL = 334.8 nm. A comparison with Raman spectra induced by oligomers leads to a correlation between the intensity of the Raman band at â 1220 cm-1 and the number of phenyl rings present in the studied material
A NEUTRON SCATTERING STUDY OF THE DENSITY OF VIBRATIONAL STATES OF FRACTAL SILICA AEROGELS
AprÚs avoir comparé les différentes méthodes couramment utilisées pour mesurer la densité d'états par diffusion inélastique des neutrons, nous présentons des spectres de diffusion purement incohérente obtenus sur des aérogels de silice, à partir de la différence entre les intensités diffusées par des échantillons identiques, protonés et deutérés. Ces résultats concernent les modes de particules et la région de haute fréquence du régime des fractons. Associées à l'information obtenue par diffusion Brillouin, ces mesures donnent l'allure générale de la densité d'états en valeur absolue, et permettent de calculer les propriétés thermiques à basse température, en excellent accord avec les résultats expérimentaux.The various methods to measure the density of states by neutron inelastic scattering are discussed. Purely incoherent scattering data on silica aerogels have been obtained by taking the difference spectra between protonated and identical deuterated samples. The results so far cover the particles modes and the upper part of the fracton regime. Complemented with Brillouin scattering information, these measurements provide an overall picture of the absolute density of states, from which low temperature thermal properties can be calculated, in remarkable agreement with experiments
POLY(PARA PHENYLENE) : SOME PROPERTIES RELATED TO THE SYNTHESIS METHOD
Le poly(para phĂ©nylĂšne) peut ĂȘtre obtenu par des mĂ©thodes diffĂ©rentes. Dans cet article, nous montrons qu'il existe des diffĂ©rences entre deux matĂ©riaux en ce qui concerne l'absorption optique, l'absorption IR, la conductivitĂ© continue et le dopage avec AsF5. D'aprĂšs ces rĂ©sultats convergents, la longueur des chaĂźnes du polymĂšre obtenu par la mĂ©thode de Yamamoto est plus faible que celle du polymĂšre obtenu par celle de Kovacic.Poly(para phenylene) can be obtained by different methods. In this paper, we show the difference between two materials in terms of optical absorption, IR spectroscopy, D.C. conductivity and AsF5 doping. According to these converging results, the chains of the polymer obtained by the Yamamoto method are shorter than those of the Kovacic polymer
Laser Direct Writing of Gold Tracks from Decomposition of Organometallic Screen Ink
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Low frequency dynamics of silica xerogel porous system
Coherent inelastic neutron and light (Raman and Brillouin) scattering measurements are reported on silica xerogels over a wide range of densities and temperatures. Raman scattering results show the presence of a boson peak at temperatures where the quasielastic contribution is negligible. The boson peak of xerogels is at a frequency around 35 cm(-1) and has a shape similar to that of melted silica. At lower frequencies (7-16 cm(-1)) another bump is visible in the Raman scattering, believed to be connected to the presence of the pores and its frequency connected to their mean sizes. This important result seems to indicate that the disorder introduced by the presence of the pores does not influence very much the density of states in the frequency range of the boson peak. A comparison is made between the Q dependence of the elastic and inelastic structure factors as a function of sample density and temperature. The absence of a peak in the inelastic structure factor for the Q value corresponding to the first sharp diffraction peak demonstrates the existence of random-phase modes for energies around the boson peak