2D Assemblies of Silicon Nanocrystallites Prepared by Sol-Gel Method from Triethoxysilane.
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2D ASSEMBLIES OF SILICON NANOCRYSTALLITES PREPARED BY SOL-GEL METHOD FROM TRIETHOXYSILANE. Jerôme Rouquette and Monique Pauthe Laboratoire de Physico-chimie de la Matière Condensée - Université de Montpellier II - Case Courrier 084 - 34095 Montpellier cedex 5 - France Michel Ramonda Laboratoire d’ Acoustique, d’ Imagerie et de Nanophysique - Université de Montpellier II - Case Courrier 082 - 34095 Montpellier cedex 5 - France Thierry Taliercio and Bernard Gil Groupe d'Etude des Semiconducteurs - Université de Montpellier II - Case Courrier 074 - 34095 Montpellier cedex 5 - France Kevin P. O'Donnell - University of Strathclyde – Glasgow-G4 ONG, Scotland The sol-gel route using triethoxysilane as a precursor has been used to prepare films of Si nanocrystallites. These films were deposited on (001)-oriented silicon substrates either by spin coating deposition of a liquid phase that was further heattreated under static vacuum (dots embedded in silica gel) or by vapour phase from the thermal decomposition under vacuum of the dried gels (uncapped dots). We address the structural characterisation of these samples and we find that a spontaneous orientation of the crystallites is obtained for heating treatment beyond 800°C if the dots are deposited in the vapour phase. The optical properties of dots embedded in silica gel reveal a strong red-orange photoluminescence due to carrier recombination at the dot surface, which is noticeably contaminated by oxygen and hydrogen. 1- Introduction Silicon is an important semiconductor for modern civilisation. Unfortunately, its optical properties are ruled by an indirect bandgap structure. Artificially reducing the sample size and dimensionality by growing silicon nanospheres is one of the approaches that are currently used to enhance the efficiency of the coupling of the electronic states with the electromagnetic field [1,2]. Under acidic or neutral hydrolysis conditions, the sol gel route applied to triethoxysilane leads to modified silica gels HSiO3/2 containing SiH bonds [3,4]. The reaction occurring may be represented as: HSi(OC2H5)3 +3/2 H2O Æ HSiO3/2 + 3 C2H5OH This property was used in a preceding study, to address the preparation and the physical properties of Si nanocrystallites embedded into a 3D-silica matrix [5]. We here focus our attention to films of Si nanocrystallites prepared by the sol-gel route using triethoxysilane as a precursor and deposited on silicon substrates. 2- Synthesis In the present section, we first present the preparation of films of Si nanocrystallites embedded in crack-free silica coatings with thickness of about 1 micrometer. Our
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method is based upon the sol-gel process and the use of triethoxysilane as the precursor for both the silica matrix and the Si crystallites. The process involves a) the synthesis of the coating solution, b) the homogeneous deposition of the liquid film by spin-coating, c) the drying process and the final densification. a) The solutions were prepared by dropping a solution of acidified water (2 moles, 0.1
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