Evidence of light-emitting amorphous silicon clusters confined in a silicon oxide matrix

International audienceAmorphous silicon oxide thin films were prepared by the coevaporation technique in ultrahigh vacuum. Different compositions were obtained by changing the evaporation rate of silicon. The samples were then annealed to different temperatures up to 950°C. The composition and the structure were investigated using energy dispersive x-ray spectroscopy, infrared absorption measurements, and Raman spectroscopy. This study attests the presence of amorphous silicon clusters in a silicon oxide matrix. Optical transmission measurements were performed and interpreted in the field of the composite medium theory. The obtained results are in good agreement with the presented structural model. The photoluminescence in the red-orange domain was studied in relation with the structure. The correlation between the photoluminescence energy and intensity and the structure shows that the light emission originates from the silicon clusters embedded in the silicon oxide matrix. Moreover the dependence of the photoluminescence energy with the silicon volume fraction suggests the origin of the light emission could be due to a quantum confinement effect of carriers in the amorphous silicon clusters

Densification of amorphous silicon prepared by hydrogen‐ion‐beam‐assisted evaporation

International audienceHydrogenated amorphous silicon films were deposited by ion-beam-assisted evaporation onto substrates maintained at 120 °C. The influence of the substrate bias was studied. By combined infrared spectrometry and thermal desorption spectrometry experiments, it is inferred that the bombardment of the growing a-Si:H film by energetic hydrogen ions produces a densification of the material without modification of the Si:H bonding

Improvement of the stability under illumination of a-Si:H films elaborated by ion-beam-assisted evaporation using a hydrogen–argon plasma

International audienceHydrogenated amorphous silicon films were deposited by ion-beam-assisted evaporation using a hydrogen-argon plasma. The influence of the substrate temperature was studied. Light induced photoconductivity decay measurements showed that high stability materials can be obtained under well defined conditions. By combined infrared spectrometry and thermal desorption spectrometry experiments, it was demonstrated that microstructure has a great influence on the stability against light induced defects

Intense visible photoluminescence in amorphous SiOx and SiOx:H films prepared by evaporation

International audienceVisible photoluminescence PL can be observed in a-SiO x and a-SiO x :H alloys prepared by evaporation of SiO in ultrahigh vacuum and under a flow of hydrogen ions, respectively. The hydrogen and oxygen bonding is studied by infrared spectrometry. The hydrogen stability is followed by thermal desorption spectrometry experiments. The evolution of the PL with annealing treatments shows that the PL can be attributed to a quantum confinement effect in a-Si clusters embedded in the matrix of a-SiO x. Hydrogen does not greatly contribute to the PL efficiency and to the thermal evolution of the a-Si clusters

Irreducible Representations of Diperiodic Groups

The irreducible representations of all of the 80 diperiodic groups, being the symmetries of the systems translationally periodical in two directions, are calculated. To this end, each of these groups is factorized as the product of a generalized translational group and an axial point group. The results are presented in the form of the tables, containing the matrices of the irreducible representations of the generators of the groups. General properties and some physical applications (degeneracy and topology of the energy bands, selection rules, etc.) are discussed.Comment: 30 pages, 5 figures, 28 tables, 18 refs, LaTex2.0

Vibrations de la molécule C

Les vibrations de la molécule C60, qui a la symétrie Ih de l'icosaèdre régulier, sont analysées. Un calcul de fréquences est discuté pour les deux vibrations totalement symétriques (Ag), qui impliquent seulement les élongations des deux types de liaisons carbone-carbone de la molécule. On démontre qu'il est impossible de rendre compte des fréquences expérimentales attribuées à ces modes en négligeant toute interaction entre les 90 coordonnées d'élongation. Ce résultat explique des désaccords systématiques signalés dans la littérature. De plus, on établit que la constante de force d'interaction entre les deux jeux de liaisons est positive

Infrared and Raman spectra of uranyl(VI) oxo-hydroxo complexes in acid aqueous solutions: a chemometric study

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Etude par spectroscopie vibrationnelle de la solvatation de l'eau par des bases organiques en matrices

L'étude des spectres infrarouge de matrices d'azote doublement dopées en eau et diméthylether (B) a permis l'identification de trois type de complexes : un complexe 1:1, HOH ... B, pour lequel les caractéristiques spectrales de la molécule d'eau (fréquence, intensité relative) sont proches de celles de la molécule d'eau donneur de proton dans le dimere (H2O)2 ; un complexe 1 : 2, de structure B . . . HOH . . . B, dans lequel la molécule d'eau conserve la symétrie C2v, et dont le tenseur polaire a ete calcule dans les hypothèses de conservation des signes des éléments du tenseur PQ et de l'intensité de la bande v2 obtenus pour le monomère : enfin un complexe 2 : 1 dans lequel une molécule d'éther se fixe sur un dimere d'eau selon l'enchaînement [math]. La comparaison avec le spectre du trimère (H2O)3 permet de discuter la structure de celui-ci

Etude par spectrometrie ultraviolette, infrarouge et Raman de l'etat de surface de sulfures avant et apres collection, en fonction de divers conditionnements

SIGLECNRS RP 440 (29) / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc