Degradation of Assembled Silicon Nanostructured Thin Films: a Theoretical and Experimental Study
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0887-Q06-04.1
Degradation of Assembled Silicon Nanostructured Thin Films: a Theoretical and Experimental Study Valeria Bertani, Luisa D’Urso, Alessandro A. Scalisi, Giuseppe Compagnini and Orazio Puglisi Dipartimento di Scienze Chimiche, Università di Catania, Viale A. Doria 6 – 95125 Catania (ITALY) ABSTRACT The study of the structures and properties of small elemental clusters has been an extremely active area of current research, due to the peculiar behavior of these species halfway between that of single atoms and of the bulk phase. In this work silicon nanoclusters are generated by ablation of a high purity polycrystalline rod with a pulsed laser vaporization source and then deposited on a support. Their structure is studied both in the gas phase by means of Time of Flight Mass Spectrometry and in the solid phase through in situ Raman and Infrared Spectroscopy. The spectra reveal that the as deposited clusters are hydrogenated with negligible amount of oxide. Degradation of silicon nanoclusters has been studied after gas exposure. In the gas of air a consistent modification was observed, leading to a near-infrared luminescent silicon nanoparticles. In the second part of the work, density functional theory is applied to investigate the geometrical structure of silicon clusters and their interaction, in term of structure and energy, with different gases. The calculations were performed with the Gaussian 03 program suite, adopting the B3LYP functional to calculate the exchange and correlation energy. Si8 has been chosen as model cluster to study the degradation of silicon clusters both kinetically and thermodynamically, in order to explain the experimental evidences. Experimental and calculated infrared spectra are compared.
INTRODUCTION In these last years a lot of work has been done on small silicon nanoparticles, both experimentally and theoretically, because of their peculiar reactivity and properties which make them useful for different applications. On the other hand, this high ratio surface/volume is responsible for cluster degradation when exposed to external agents. As an example, thin film hydrogenate amorphous silicon is a technically and economically-feasible material for solar cells but, due to the presence of hydrogen atoms, as it results from molecular dynamics calculations, it undergoes upon light-induced degradation [1]. An useful way to prevent the degrade of silicon nanoparticles, especially of their photoluminescence, is the creation of a protective layer on their surface by embedding them in a polymer, or by refluxing a silicon nanoparticle dispersion in the presence of an alkene [2] or by means of a UV-induced graft polymerization of acrylic acid on particle surface [3]. In the present study, degradation of silicon nanoparticles, produced by Low Energy Cluster Beam Deposition, was investigated both experimentally and theoretically. In particular, reactions of small silicon clusters with hydrogen and oxygen were studied.
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0887-Q06-04.2
Silicon clusters were obtained b
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