Modulation of stoichiometry, morphology and composition of transition metal oxide nanostructures through hot wire chemic
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Matthew Brier, Ajinkya Puntambekar, and Thomas DiGiovanni Howard P. Isermann Department of Chemical and Biological Engineering, Rensselaer Polytechnic Institute, Troy, New York 12180, USA (Received 30 May 2015; accepted 19 November 2015)
A hot wire chemical vapor deposition technique is described for synthesis of 1D nanostructures of a controlled morphology, stoichiometry, and composition. The synthesis involves the evaporation and condensation of metal oxide vapor through the reaction of oxygen with the hot filaments of respective transition metals. The stoichiometry and morphology of MoO3 and WO3 were modulated by varying the filament temperature and partial pressure of oxygen in the growth chamber. Based on the results under different conditions, a morphological phase diagram, and a growth model based on the extent of gas phase supersaturation were developed to understand the growth mechanism. Further, ternary transition metal oxide, NiMoO4, was synthesized as a proof-of-concept for tuning the composition of deposition through simultaneous evaporation of two metal oxides. Vidhya Chakrapani is currently an Assistant Professor with a joint appointment in Dept. of Chemical and Biological Engineering and Dept. of Physics at Rensselaer Polytechnic Institute. She completed her PhD at Case Western Reserve University in 2007 and went on to postdoctoral studies at the Georgia Institute of Technology and Notre Dame Radiation Laboratory. For the past 15 years, her research has been focused on the various fundamental and applied aspects of semiconductor electrochemistry, including solar cells, Li ion batteries, and smart windows. For her work on diamond electrochemistry, she was awarded the “Outstanding Young Researcher” award from the Sigma Xi Research Society, Louisville in 2008. In addition, she has won the CBE Outstanding Teaching award and Young Investigator awards from JNCASR (India) and the Indian Institute of Science. She has published more than 25 papers in this field along with 3 patents. Vidhya Chakrapani
I. INTRODUCTION
In the past decade, transition metal oxides (TMOs) have gained significant attention due to their outstanding catalytic, ferroelectric, superconducting, and optical properties. Such a diverse array of properties has resulted in their use in various applications such as heterogeneous catalysis, sensors, solar cells, and batteries. One of the unique features of TMOs is the dependence of their band gaps, and hence their electrical conductivities, on stoichiometry. TMO stoichiometry can be modulated from the insulating (e.g., V2O5, ;2.2 eV) to the semiconducting (e.g., VO2, ;0.7 eV) to the metallic state (e.g., VO, no gap) by changing the Contributing Editor: Cewen Nan a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2015.366 J. Mater. Res., Vol. 31, No. 1, Jan 14, 2016
concentration of anionic or cationic vacancies in the lattice. Both experimental and theoretical studies have shown that many of the unique properties of metal oxides arise as a result of the compl
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