Synthesis of Cadmium and Lead Telluride Nanoparticles: Examples of Oriented attachment Growth Mechanism
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Synthesis of Cadmium and Lead Telluride Nanoparticles: Examples of Oriented attachment Growth Mechanism Neerish Revaprasadu1 1
Department of Chemistry, University of Zululand, Private bag X1001, KwaDlangezwa, 3880. E-mail: [email protected] ABSTRACT The synthesis of hexadecylamine capped (HDA) CdTe and PbTe via a simple hybrid solution based high temperature route is described. In this method the tellurium is first reduced to form the telluride salt followed by reaction with the metal salt and finally thermolysis in a coordinating solvent. The metal salt and reaction temperature played an important role in the morphology and growth mechanism of the particles. The CdTe particles where in the form of rods and spheres whereas the PbTe nanoparticles were in the form of nanowires. The oriented attachment mechanism is proposed for the growth of elongated particles under certain reaction conditions. INTRODUCTION The synthesis of nanomaterials with controlled size and shape has now become a mature area of science. Materials in the nanosize dimension can be synthesized with a large degree of ease, control and in large quantities. Semiconductor materials such as metal chalcogenides have found applications in diverse fields in which the size and surface effects are the determinant factors in the device performance. CdTe is a useful material because of its high photoluminescence (PL) quantum efficiencies making it an important material for applications in light emitting devices [1], photovoltaic and photoelectrochemical devices [2] and biological labels [3]. PbTe is an important narrow band gap semiconductor material with a large excitonic Bohr radius (~46 nm) [4]. While the synthesis of nanomaterials has become a routine technology, the growth mechanism and in particular the crystallization of the materials at the nanoscale is still not well understand. The classical crystal growth kinetic model, LaMer and Ostwald ripening theories have been the widely accepted as the mechanism of crystal growth. The initial nucleation and growth is explained by the Gibbs-Thompson law [5]. In this model, atoms or molecules continually bond and coalesce, thereby attaching itself to the surface of larger crystal seeds. Recently a novel growth process known as oriented attachment (OA) has been identified as a mechanism for nanocrystal growth [6]. In this growth mechanism particles are fused through combination of high energy facets forming a mesocrystal that results in the overall lower surface energy of the particles. The advantage of this type of growth is the synthesis of defect free one dimensional crystals. Pradhan et al. reported the synthesis of CdSe nanowires by the OA growth mechanism [7]. They used alkylamines with differing chain lengths and also varied the reaction temperatures to obtain nanowires with diameters between 1.6 and 6 nm. Kotov et al. also demonstrated the formation of CdTe nanowires via crystal dipole-induced self-assembly of CdTe nanoparticles [8]. The removal of the protective shell allowed the assembly of the
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