Synthesis of III-V Nanocrystals by Co-reduction Reactions
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Synthesis of III-V Nanocrystals by Co-reduction Reactions Zhaoping Liu, and Jiye Fang Department of Chemistry, State University of New York at Binghamton, Binghamton, NY, 13902 ABSTRACT This paper describes a co-reduction colloidal method for the synthesis of In-containing III-V nanocrystals (NCs) by using pnictogen halides (such as PCl3, AsCl3, and SbCl3) as the pnictogen-sources and superhydride (LiBH(C2H5)3) as the reducing agent. The syntheses were generally carried out in octadecene in the presence of fatty acids at ~250 ºC. The as-synthesized InP NCs were quasi-monodisperse in particle size and size distribution, whereas the InAs and InSb NCs showed relatively lower quality. The growth process of NCs was studied using InP as a model system. INTRODUCTION Colloidal III-V semiconductor nanocrystals (NCs) have attracted intense interest during the last two decades due to their unique effects of quantum confinement. However, chemical synthesis of them is much less advanced compared to the II-VI analogues due to their higher degree of covalent bonding [1-5]. The synthetic methods for III-V NCs are initially developed on the basis of dehalosilylation reactions [6]. These methods usually involve the reaction between a metal salt, such as GaCl3 or InCl3, and tris(trimethylsilyl)pnictogen, E(TMS)3 (E = P, As, or Sb), in a high-boiling-point solvent at a high temperature. Controllable synthesis of III-V NCs was first achieved by the use of coordinating solvents (such as TOPO and TOP) as the reaction media [7-9]. To obtain crystalline NCs, the growth must be carried out over a long period of time (up to seven days) at a temperature ranging from 200-400 ºC. Even then, the as-synthesized NCs showed a broad size distribution, and a further size-selective post-treatment was required to achieve monodispersity. Later, Battaglia and Peng further developed this synthesis by replacing the phosphorous-based coordinating solvent with a noncoordinating one such as octadecene and using fatty acids as the capping ligands [10]. This synthetic variation not only greatly shortened the reaction time to a few hours but also generated monodisperse InP and InAs NCs without any size sorting. Recently, Xu et al. showed that similar-quality InP NCs could also be rapidly produced in some weak coordinating solvents such as fatty acid esters [11]. However, all of these successful syntheses are dependant on the use of the expensive E(TMS)3 precursors as the pnictogen-sources. This results in a high cost, hampering scale-up of the synthesis. To lower the cost of the synthesis, some other pnictogen compounds have been explored as the alternative pnictogen-sources. For instance, the decomposition of single-source precursors (organometallic compounds) could directly yield III-V nanocrystals [12,13]; pnictide compounds, E(Na/K)3, were used for the straightforward syntheses of III-V nanocrystals [14,15]. However, the replacement of E(TMS)3 by organometallic compounds or E(Na/K)3 leads to much less control over the particle size. Moreover, th
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