Si-N nanowire formation from Silicon nano and microparticles.
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Si-N nanowire formation from Silicon nano and microparticles. Chandana Rath1, A. Pinyol2 J. Farjas1, P. Roura1 and E. Bertran2 1
GRM, Department de Fisica, Universitat de Girona, Campus Montilivi, E17071 Girona, Catalonia, Spain 2 FEMAN, Department de Fisica Aplicada i Òptica, Universitat de Barcelona, Av. Diagonal 647, E08028 Barcelona, Catalonia, Spain Corresponding author: E-mail: [email protected] ABSTRACT We report silicon nitride whisker formation from hydrogenated amorphous silicon (a-Si:H) nanoparticles grown by PECVD for the first time. We compared the results with the kinetics of whisker formation from ball milled crystalline silicon (c-Si) microparticles. Whisker formation is analyzed at different temperatures (900-1440 oC) and oxygen partial pressures. At temperatures equal or above 1350 C and at low oxygen partial pressure we observe monocrystalline α-Si3N4 whiskers having 30-100 nm diameter and several microns length. By increasing the oxygen partial pressure, the structure of whiskers is completely changed, as shown by electron microscopy. In this case we observe α-Si3N4 whiskers covered by an amorphous silica layer at 1350 C. Finally, when the precursor material is silicon microparticles, thicker (170-330 nm) and longer whiskers are formed. INTRODUCTION Silicon nitride is an advanced ceramic and has the potential to be used in various applications thanks to its enhanced mechanical, chemical, electronic and thermal properties. They include, high mechanical strength with good flexibility, light weight, high fracture toughness, enhanced resistance to thermal shock and to oxidation [1-3]. These properties are related to the highly covalent chemical bonding between silicon and nitrogen atoms [4]. Therefore, studies of the synthesis of silicon nitride whiskers have received extensive attention and various synthesis methods have been developed to improve their properties. Among them we can find carbothermal reduction of silica-containing compound [2,5-7], chemical vapor deposition process [8-11], nitridation of silicon compacts (RBSN) [12-13] and combustion synthesis [1416]. Some of these processes are very slow and energy consuming [12], and in some cases a very high temperature (1900ºC) is required [16]. Besides, Si3N4 can not be formed from silicon suboxide prepared by carbothermal reduction [6]. In the present paper we report the formation of silicon nitride from a-Si:H nanoparticles and c-Si microparticles. As far as we know, there is not any publication related to whisker formation from amorphous silicon nanoparticles. We distinguish two competing processes such as oxidation and nitridation over the temperature range taken (900-1450 oC). By varying the temperature, the oxygen partial pressure and the specific surface area of Si particles we could produce α-Si3N4 whiskers in a wide range of diameters and lengths.
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EXPERIMENTAL a-Si:H nanoparticles have been prepared by plasma-enhanced chemical vapour deposition (PECVD) method from a RF glow-discharge of silane. c-Si microparticles
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