A Novel Spray Based Method for the Production of Semiconductor Nanocrystals
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A Novel Spray Based Method for the Production of Semiconductor Nanocrystals
Lilac Amirav and Efrat Lifshitz Department of Chemistry, Solid State Institute and Russell Berrie Nanotechnology Institute, Technion, Haifa 32000, Israel, ABSTRACT We present a novel spray based method for the formation and production of semiconductor nanocrystals that provides an attractive alternative to the commonly used epitaxial and colloidal procedures. According to this spray-based method, mainly thermospray, solutions of semiconductor salts are first sprayed into monodispersed droplets, which subsequently become solid nanoparticles by solvent evaporation. A semiconductor nanoparticle is produced from a single spray droplet upon the full vaporization of the solvent. The average diameter and size distribution of the final nanocrystals are controlled and determined by the solute concentration of the sprayed solution and by the droplet size, hence by the spray production parameters. The spray-produced nanocrystals are collected on any selected solid support. Representative results, shown in this paper, reveal the formation of CdS nanocrystals in the size range of 3 to 6 nanometer and with a size distribution of as low as five percents. A further structural analysis of these nanocrystals showed that they were formed in the zinc blend phase with high degree of crystallinity. INTRODUCTION In the last two decades significant attention has been devoted to the physics of low dimensional semiconductor structures. Among those, semiconductor nanoparticles are of particular interest, due to the pronounced influence of the three-dimensional size confinement on their electronic and optical properties [1-6]. Extensive effort has been devoted to the production of high quality semiconductor nanoparticles, motivated by their potential use in new and emerging technologies. Currently, there are two main methods for the fabrication of semiconductor nanoparticles, namely epitaxial growth [7] and colloidal chemistry techniques [8-11]. Epitaxial growth of nanoparticles produces relatively large dots, with weak quantum confinement [12]. The liberty to choose the substrate is limited, and the nanoparticles cannot be assembled to a closed pack array. Furthermore, this method requires ultra high vacuum as well as other complex and expensive equipment. The colloidal method requires inert and elevated temperature conditions, enabling reproducible formation of nanoparticles, with a variety of sizes and shapes, with initial distributions of about 10% in diameter, and with some control on surface properties. However, doping of colloidal nanoparticles is inhibited due to the large diffusivity of the dopant to the nanocrystalline's surfaces at the elevated temperatures required. Furthermore, the organic capping plays a key-role in any selfassembly created by these nanoparticles, preventing the formation of highly packed structures. Such closed pack arrays of nanoparticles have potential uses in any future application where good conductivity properties are requi
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