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Multilayer adsorption of gases on graphite studied by ellipsometry / Mahrez Drir 

Public ISBD Titre : Multilayer adsorption of gases on graphite studied by ellipsometry Type de document : texte imprimé Auteurs : Mahrez Drir, Auteur ; George B. Hess, Directeur de thèse Editeur : University of Virginia Année de publication : 1986 Importance : 156 f. Présentation : ill. Format : 27 cm. Note générale : Thèse de Doctorat : Physique : Virginia, University of Virginia : 1986 Bibliogr. f. 157 - 165 Langues : Anglais (eng) Mots-clés : Adsorption  --  gases Single  --  cleaved  surface Highly  oriented  pyrolitic  graphite Ellipsometric  technique Index. décimale : D002486 Résumé : In this work we report adsorption measurements on a single cleaved surface of highly oriented pyrolitic graphite (HOPG). This eliminates the possibility of capillary condensation, while providing a surface with larger facet size and better energy uniformity than exfoliated graphite. We have measured adsorbate coverage by a phase-modulation ellipsometric technique, using laser light reflected from a 0.1 x 0.2 mm spot on the graphite surface. We have studied various gases (Kr, O₂, C₂H₄ and CF₄) in the vicinity of their respective bulk triple point Tt (except for the case of Kr where all the data were recorded below Tt). We have observed layer-by-layer adsorption where as many as nine steps could be seen. The overall features were characteristic of wetting at the triple point: below Tt, bulk crystallite formation preempts film growth after a limited number of layers. Above Tt, the film grows to a thickness equivalent to about 40-50 layers. However, indications of bulk droplets appear above about 10-12 layers. Our results suggest not quite complete wetting by the liquid phase of the various gases studied. Multilayer adsorption of gases on graphite studied by ellipsometry [texte imprimé] / Mahrez Drir, Auteur ; George B. Hess, Directeur de thèse . - [S.l.] : University of Virginia, 1986 . - 156 f. : ill. ; 27 cm. Thèse de Doctorat : Physique : Virginia, University of Virginia : 1986 Bibliogr. f. 157 - 165 Langues : Anglais (eng) Mots-clés : Adsorption  --  gases Single  --  cleaved  surface Highly  oriented  pyrolitic  graphite Ellipsometric  technique Index. décimale : D002486 Résumé : In this work we report adsorption measurements on a single cleaved surface of highly oriented pyrolitic graphite (HOPG). This eliminates the possibility of capillary condensation, while providing a surface with larger facet size and better energy uniformity than exfoliated graphite. We have measured adsorbate coverage by a phase-modulation ellipsometric technique, using laser light reflected from a 0.1 x 0.2 mm spot on the graphite surface. We have studied various gases (Kr, O₂, C₂H₄ and CF₄) in the vicinity of their respective bulk triple point Tt (except for the case of Kr where all the data were recorded below Tt). We have observed layer-by-layer adsorption where as many as nine steps could be seen. The overall features were characteristic of wetting at the triple point: below Tt, bulk crystallite formation preempts film growth after a limited number of layers. Above Tt, the film grows to a thickness equivalent to about 40-50 layers. However, indications of bulk droplets appear above about 10-12 layers. Our results suggest not quite complete wetting by the liquid phase of the various gases studied.

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