Convenient Molecular Approach of Size and Shape Controlled ZnSe and ZnTe Nanocrystals
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Convenient Molecular Approach of Size and Shape Controlled ZnSe and ZnTe Nanocrystals Young-wook Jun, Jong-Il Park and Jinwoo Cheon* Department of Chemistry and School of Molecular Science – BK21, Korea Advanced Institute of Science and Technology (KAIST), Taejon 305-701, Korea ABSTRACT Our study describes a convenient one-step synthesis of ZnSe and ZnTe nanocrystals (NC) whose sizes and shapes are precisely tuned by varing the growth temperature or stabilizing surfactants. We utilized molecular precursors, bis(phenylselenolate or phenyltellurolato)zinc -N,N,N’,N’-tetramethylethylenediamine (TMEDA), which effectively produce 0-dimensional sphere or 1-dimensional nanorods of ZnSe or ZnTe, respectively. Nanocrystals are highly monodispersed and luminescent; the emission wavelength varies over a wide range depending on the particle size. This study constitutes a nice demonstration of direct size and shape controlled synthesis of semiconductor nanocrystals and this method can be extended to the synthesis of nanocrystals of other materials.
INTRODUCTION Controlled synthesis of inorganic nanocrystals is one of the most important issues in nanocommunity because their size and shape act as important parameters for optical and electronic properties. Especially, 1-dimensional nanocrystals have drawn special attention because of novel properties due to their anisotropic crystal structure [1, 2]. Shape control of nanocrystals can be achieved in gas phase by several methods. One of the methods is template-assisted or strain-assisted synthesis in gas phase. For example, crystal growth inside a nanoporous solid, such as silica ball template, MCM-41, leads to the formation of nanorods, nanowires, and nanoballs [3, 4]. Pyramidal dots or nanowires can be obtained using strain-assisted epitaxial growth [5]. Lieber et al. reported that a solid rod can be obtained using vapor-liquid-solid growth [6] and Buhro et al. demonstrated solid rods also obtained by solution-liquid-solid growth [7]. The other means of controlling nanocrystals is colloidal synthesis using micelle templates. Mann et al. show that prismatic BaCrO4 nanocrystals can be obtained by introducing Ba2+ and CrO4- ion in AOT microemulsion using structured AOT micelles [8]. Nanorods were prepared by electrochemical reduction method [9], hydrazine reduction method [10], and simple ionic reactions [11]. Recently, a nonhydrolytic synthesis of CdSe nanorods in hot mixture of trioctylphosphine oxide and hexylphosphonic acid was reported [1]. In this paper, we demonstrate size and shape controlled ZnE (E=Se, Te) nanocrystals with quantum confinement effects. Shape of zinc chalcogenide nanocrystals is controllable either spherical or rod-like structure depending on the choice of stabilizing surfactants. Furthermore, the size of spherical nanocrystals is controlled by the growth temperature.
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EXPERIMENTS Trioctylphosphine (Aldrich) was used as received, while trioctylamine, and dimethylhexylamine were distilled before use. Trioctylphosphine oxide (TOPO) dodecylamine (Aldri
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