Tellurium nanotubes and nanorods synthesized by physical vapor deposition
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Tellurium nanotubes and nanorods were synthesized by physical vapor deposition (PVD) in an induction furnace for reaction times between 25 and 35 min. The growth morphologies depended on the reaction times and the atmosphere in the induction furnace. Nanotubes grew only under argon atmosphere (1 mbar). Under vacuum, tellurium blades and nanorods were observed. Of particular interest are the dense carpets of nanorods observed on polycrystalline aluminum. PVD experiences in a conventional high vacuum coating system did not lead to the formation of nanotubes nor nanorods. The interesting electrical properties of tellurium and tellurium compounds combined with the observed growth morphologies are promising for the fabrication of nanoscale functional devices.
I. INTRODUCTION 1
The discovery of carbon nanotubes in 1991 has initiated an intensive search for other materials that may form hollow one dimensional nanostructures. These materials have promising application as nanoelectronic, optoelectronic, electrochemical, and electromechanical devices among others.2 The search was concentrated on compounds with layered structures and successful synthesis of nanotubes were reported for materials such as boron nitride3–6 and tungsten disulfide (WS2).7,8 Other likely candidates that might crystallize in tubelike morphology are phases with one-dimensional structure elements. Since 2002, different groups were able to synthesize tellurium nanotubes through wet chemical routes.9–12 Tellurium is an element with a structure consisting of helical chains parallel to the c axis. Mayers and Xia used a precipitation technique known as the “polyol process.”13 Elemental tellurium nanotubes formed when ethylene glycol was added as reducing agent to an orthotelluric acid solution. A large number of euhedral seed crystals were formed by homogeneous nucleation. Preferential growth at the seed edges led to the development of tubes growing along the [001] and [00-1] directions. The tubes had very well defined hollow interiors with the seed crystal as plug in the center. The crystal dimensions have been controlled by adjusting the concentrations of the reactants. Other compounds with rodlike or tubelike morphology synthesized by the same wet chemical route are (Se, Te)13—solid solutions and Ag2Se.14 In 2003, Wei et al. used a solvothermal process
DOI: 10.1557/JMR.2004.0277 J. Mater. Res., Vol. 19, No. 7, Jul 2004
http://journals.cambridge.org
Downloaded: 17 Mar 2015
with N, N-dimethyformamide as solvent, KOH as reducing agent and porous silicon (MCM-41) as growth assistant to synthesize tellurium nanotubes.11 In this case, the crystallization of tellurium in the form of nanotubes is related to the nano-porous structure of MCM-41 used as template. In 2003, Se nanorods were produced on glass by laser ablation under controlled temperature by Jiang et al.15 In this study, we report the formation of tellurium nanotubes and nanorods through physical vapor deposition (PVD) in an induction furnace under controllable experimental conditions and in high
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