Wet Synthesis and Characterization of MSe (M = Cd, Hg) Nanocrystallites at Room Temperature
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Semiconductor selenides of MSe (M ⳱ Cd, Hg) nanocrystalline powders were synthesized through the reactions between metal chlorides and sodium selenosulfate in the ammoniacal aqueous solution at room temperature for 6–10 h. The samples were characterized by x-ray powder diffraction, transmission electron microscopy, electron diffraction, x-ray photoelectron spectroscopy, and elemental analysis. The average diameters of CdSe and HgSe nanocrystallites are 4 and 8 nm, respectively. The storage and an interesting phase transition under hydrothermal conditions have been presented. The absorption spectrum of the as-prepared samples exhibits obvious blue shift due to the size confinement.
I. INTRODUCTION
The synthesis and characterization of nanostructured materials have attracted much attention over the last several years due to their unconventional properties.1 Particularly, semiconductor nanoparticles exhibit novel catalytic, optoelectronic, and electrical properties.2–4 The different properties between the nanocrystallites and bulk material are mainly caused by the surface effects and size effects (quantum size effects). For example, being an important semiconductor, bulk CdSe has an optical band gap at 716 nm, but the optical absorption edge of CdSe nanocrystallites with 1.2–11.5-nm diameter has a considerable blue shift.5 Cadmium and mercury selenides belong to the II–VI group semiconductors, which have been conventionally prepared by elemental reactions.6 This method is important and widely used to prepare II–VI chalcogenides. Meanwhile, other techniques such as chemical solution deposition and ionic reaction,7–9 the molecular precursor method,5,10–12 gas–liquid precipitation,13 and electrochemical,14,15 sonochemical,16,17 ␥-irradiation,18 and solvothermal19 methods have been employed to synthesize the selenides. In contrast, the solution reaction growth technique appears to be the cheapest and most convenient approach to prepare the selenides7,20,21 because it does not involve complex instrumentation and growth rate is easily controllable. Recently, the solution
technique has attracted considerable interest to the materials chemistry community on the research of II–VI semiconductor nanocrystallites.22 Selenosulfate and selenourea are the main selenium sources to afford Se2− ions for the preparation of selenides through reactive solution growth. However, selenourea is expensive and not readily available. Thus, selenosulfate is a better Se2− source for solution preparation of selenides. Kitaev’s group first employed selenosulfate as Se2− source to synthesize selenides through a chemical solution deposition route in the CdCl2–NH4OH–NaSeSO3–KOH system.7 Thereafter, other groups also prepared selenides using selenosulfate as a Se2− source. For example, Skyllas-Kazacos et al.23 used selenosulfate to synthesize selenides through electroreduction deposition in aqueous solution. Pramanik et al.24 has also prepared several semiconducting films of selenides from selenosulfate by the solution technique. In our work, we synthe
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