Silicon Nanoclusters in Si-SiO 2 System
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Silicon Nanoclusters in Si-SiO2 System F.J. Espinoza-Beltrán1, L.L. Díaz-Flores1, J.M. Yáñez-Limón1, J. Morales-Hernández2, F. Rodríguez-Melgarejo1, Yuri Vorobiev1, and J. González-Hernández1 1 Centro de Investigación y de Estudios Avanzados del IPN, Unidad Querétaro. Libramiento Norponiente 2000, Fracc. Real de Juriquilla, Querétaro, Qro., México. 2 Programa de Posgrado de Ingeniería, Universidad Autónoma de Querétaro, México. ABSTRACT Low concentration of Si nanoparticles (n-Si) produced by a ball milling method were introduced into a SiO2 matrix by the sol-gel method. These SiO2 sol-gel suspensions were prepared with high water-TEOS ratios. The samples obtained have high silanol concentration as was proved by infrared spectroscopy. The silanol structures of this samples are resistant for temperature as high as 800°C. Raman scattering measurements showed evidence of a photo-oxidation effect of the nSi particles embedded into the SiO2 matrix with high silanol concentration. The nanometric size of the Si particles was computed from Raman scattering measurements. The photo-oxidation effect was observed as a gradual shifting and broadening of the Raman signal due to the reduction of the particle size from 14 to 7 nm. INTRODUCTION Si nanoparticles embedded into a SiO2 matrix has been a goal for several researchers in the last years [1-3]. L. Zhang et al reported an interesting procedure to obtain n-Si into SiO2 matrix, introducing Si particles from porous Si by the sol-gel method [4]. An alternative method to obtain n-Si is the high energy ball milling, which allows to obtain nanometric particles after 30 minutes of milling. After the selection of the smallest particles from the milled Si powder, it is possible to obtain samples of SiO2 with n-Si embedded by using the sol-gel method. The effective particle size can be reduced by the oxidation effect due the chemical reaction de n-Si with water and alcohol contained in the sol-gel solution. Additional thermal annealing improve the former chemical reactions reducing the size of the Si particles. The final Si nanoparticles or clusters are surrounded by SiOX and Si-OH (silanol) structures. In this work we study the effects of the introduction of Si nanoparticles into a SiO2 matrix made by sol-gel method using solutions with high water-TEOS ratios. We are interested to study the effect of thermal annealing in the range from room temperature to 800°C on the SiO2 matrix and also on the n-Si embedded. A very fine powder of small Si particles is obtained from Si grains by a ball milling process. The method to select a narrow distribution of Si particle size consisted in suspension milled of the Si powder into ethanol-nitric acid solution during 24 h. Later we introduced an additional milling process [5] by using a ball mill to disperse n-Si in the SiO2 matrix. The samples were studied by infrared and Raman scattering measurements. EXPERIMENTAL DETAILS Preparation of small particles of Si: By using a high energy ball mill SPEX-mill/mixer mod. 8000, granular silicon of 99.999% pu
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