Formation and Cathodoluminescence of Silicon Nanoclusters in Silica
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Formation and Cathodoluminescence of Silicon Nanoclusters in Silica Maria V. Zamoryanskaya, Vladimir I. Sokolov Ioffe Physico-Technical Institute, 26, Polytecknycheskaya st, St. Petersburg, Russia 194021, email: [email protected], fax.7-812-2471017.
ABSTRACT The process of formation of silicon nanoclusters in a silicate matrix by the focused electron beam of high power and their cathodoluminescent properties were studied in this paper. The size of the silicon clusters and their concentration depend on the electron beam power and on the properties of the silicate matrix (density, porosity, composition). In this paper we studied the evolution of cathodoluminescent properties in bulk silicon oxide, porous silicon oxide glass, silicagel (n·SiO2·m·H2O) and opal. The result of the modification of silica is the appearance of the CL bands at 2.3eV in green region, and the bands at 1.4 and 1.1eV. The CL intensity of these bands increases during the interaction with electron beam. The volt-ampere characteristics of the modified areas of the silica are non-linear and depend on the time of the interaction and the power of the electron beam. We relate the appearance of these new CL bands with formation of oxygen-deficit defects and silicon clusters. INTRODUCTION The search for new composite materials is very important in creating new optical and magnetic devices. Silicon based material with nanoscale crystallites is very attractive because it has unique electrical and optical properties and photoluminescence in the visible, UV and IR ranges. There are various routes to synthesize the systems consisting of SiO2 matrix and silicon nanocrystallites, these are silicon nanocrystallites in buried SiOx layers, superlattices Si/SiO2, synthetic opal and zeolite with silicon nanocrystals in voids. In this work we studied a modification of silicon oxide by an electron beam of high power and a relationship between an appearance of Si nanoscale crystallites as a result of the modification and the changes in luminescence and conductivity of the modifiied areas. The partly reduction of silicon oxide is possible in vacuum at a temperature 200-800oC. The existence of an interface plays a very important role in this process [1]. The presence of different types of interfaces initiates the process of reduction of silicon oxide to silicon. It may be Si/SiO2 interface for SiO2 films on silicon or some admixture or impurity in bulk silicon oxide [2]. In our case of bulk non-doped silicon oxide these are interfaces between matrix and pores, nanopores, channels. That is why we study the formation of silicon clusters in matrix with different density and porosity. The next important factor for formation of silicon clusters is the radiation damage and local heating of silicon oxide as a result of interaction between the electron beam and an oxide matrix. We estimate a value of the local temperature using formula suggested by Castaing [2]. If the electron current is 10 nA and diameter - 3 µ k the increase of the temperature ( ∆ T) is about 100
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