Deposition of zinc sulfide quantum dots from a single-source molecular precursor
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Deposition of zinc sulfide quantum dots from a single-source molecular precursor N. Revaprasadu Department of Chemistry, Imperial College of Science, Technology and Medicine, South Kensington, London SW7 2AZ, United Kingdom, and Department of Chemistry, University of Zululand, Private Bag X1001, Kwadlangezwa 3886
M. Azad Malik and P. O’Brien Department of Chemistry, Imperial College of Science, Technology and Medicine, South Kensington, London SW7 2AZ, United Kingdom
G. Wakefield Department of Engineering Science, University of Oxford, Parks Road, Oxford OX1 3PJ, United Kingdom (Received 1 September 1998; accepted 10 May 1999)
Nanoparticles of ZnS capped with tri-n-octylphosphineoxide (TOPO) and close to monodispersed have been prepared by a single-source route using ethyl(di-ethyldithiocarbamato)zinc(II) as a precursor. The nanoparticles obtained showed quantum size effects in their optical spectra, and the photoluminescence spectrum showed a broad emission that could be attributed to the surface traps. A blue shift of 0.31 eV in relation to the bulk material was observed. The selected area electron diffraction, x-ray diffraction pattern and transmission electron microscopy showed the material to be of the zinc blend structure. The crystallinity of the material was also evident from high-resolution transmission electron microscopy, which gave well-defined images of nano-sized particles with clear lattice fringes and a spacing of approximately 3 Å, corresponding to the (111) planes of the cubic crystalline ZnS phase and in the size range of 3.9–4.9 nm. The presence of strong phosphorus peak in the energy dispersion analytical x-ray pattern, together with a shift in infrared band for P ⳱ O of TOPO showed that the particles were TOPO capped. I. INTRODUCTION
II. EXPERIMENTAL
Nano-sized semiconductor particles are materials that are intermediate between molecules and the bulk species. Such materials have been the source of considerable interest because of their unique and potentially tunable properties (i.e., size quantization effects on nonlinear optical behavior and luminescence spectra).1–9 Bulk ZnS and Mn-doped ZnS thin films are used as phosphors and in electroluminescent devices.10 Such properties have made the study of ZnS and Mn-doped ZnS the subject of intensive research.10–18 Nano-sized ZnS and Mn-doped ZnS have been prepared by colloidal routes10–14 in structured media such as polymers and gel films15–17 and by thermolysis of elemental zinc and sulfur in a coordinating solvent.18 In this article we report the synthesis of tri-noctylphosphineoxide (TOPO)-capped ZnS nanoparticles by a single source route.19–21
A. Chemicals
Diethylzinc, dichloromethane, diethylamine, sulfur, TOPO, tri-n-octylphosphine (TOP) were purchased from Aldrich Chemical Company Ltd., and methanol, petroleum ether (40–60 °C), and toluene from British Drug Houses (BDH). TOPO was purified by use of the literature method. The solvents used for air-sensitive work were distilled, deoxygenated
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