The General Synthesis of Nanostructured V/VI Semiconductors
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The General Synthesis of Nanostructured V/VI Semiconductors Paul Christian & Paul O’Brien School of Chemistry & The Manchester Material Science Center, University of Manchester, Oxford Road, Manchester, M13 9PL. UK. E-mail [email protected], paul.o’[email protected].
Abstract Semiconductors in the V/VI series have band gaps ranging from 2.2 eV for Sb2S3 to 0.21 eV for Bi2Te3 spanning the range seen from conventional mid to narrow band gap materials to semi-metals. These materials, especially those with narrower band gaps, demonstrate thermo-electric properties and are used in Peltier devices. There are examples in the literature of the synthesis of several of these materials in a nanostructured form, however the reactions often rely on highly toxic reagents, especially in the case of tellurium containing materials. Further more there are no reports of general routes applicable to all three chalcogenides. In this paper we describe a general method for the synthesis of chalcogenide V/VI nanomaterials by the reaction of acetate salts with the corresponding chalcogenide under reflux conditions in long chain alkyl amines, typically octylamine or dodecylamine. The effect of temperature and capping agent on the morphology of the final product are discussed and in particular the synthesis of Bi2S3 nanorods, Bi2Se3 and Bi2Te3 nanowafers and Sb2Se3 nanowires are described.
Introduction There is much contemporary interest in the preparation of V/VI semiconductors for optical data storage, electroacive materials, thermoelectric coolers and photodiode arrays. [1] In particular these applications will be improved by the development of nanostructured materials of this type. V/VI materials such as Bi2Se3 and Sb2Te3 have exceptionally small band gaps. However, there are very few reports of the synthesis of bismuth or antinomy chalcogenides as nanomaterials. Generally these nanomaterials have been prepared by hydothermal [2] or solvothermal [3] methods, by the polyol process [4] or sonochemistry. [5] It is interesting to demonstrate a system that can be easily applied to all six semiconductors.
Experimental Sulfur, selenium, tellurium, bismuth acetate, antinomy acetate, octylamine and dodecylamine were purchased from Aldrich and used as received. The metal acetate (500 mg) was dissolved in the amine and the mixture degassed for 1 hour, with heating (~ 80 ºC) in the case of dodecylamine. The chalcogenide was dissolved or suspended in the appropriate amine. The degassed reaction solution was brought to reflux (or the reaction temperature) and the chalcogenide added. The reaction
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was then heated for 90 mins (10 hr in the case of Te). After cooling the product was isolated by precipitation with methanol and cleaned by washing with toluene and reprecipitation with methanol. TEM samples were prepared by suspension in toluene followed by evaporation onto a carbon coated grid. SEM samples were prepared by careful sprinkling of the sample onto an adhesive carbon tab mounted on an aluminum stub and coating with amorph
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