Evolution of titanium dioxide one-dimensional nanostructures from surface-reaction-limited pulsed chemical vapor deposit
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Evolution of titanium dioxide one-dimensional nanostructures from surface-reaction-limited pulsed chemical vapor deposition Xudong Wanga) and Jian Shi Department of Materials Science and Engineering, University of Wisconsin–Madison, Madison, Wisconsin 53706 (Received 6 May 2012; accepted 17 October 2012)
This paper reviews the recent development of surface-reaction-limited pulsed chemical vapor deposition (SPCVD) technique for the growth of TiO2 one-dimensional nanostructures. SPCVD uses separated TiCl4 and H2O precursor pulses, and the anisotropic growth of TiO2 crystals is attributed to the combined effects of surface recombination and HCl restructuring at high temperature during elongated purging time. Therefore, the crystal growth is effectively decoupled from precursor vapor concentration, which allows uniform growth of TiO2 nanorods (NRs) inside highly confined spaces. The phase of TiO2 NRs can be tuned from anatase to rutile by raising the deposition temperature. Au catalysts are able to enhance the growth rate and led to bifurcated nanowire (NW) morphology. A high density three-dimensional (3D) NW architecture was created by SPCVD growing TiO2 NRs inside dense Si NW forests. Such 3D structures offer both large surface area and excellent charge transport property, which substantially improved the efficiency of photoelectrochemical devices.
I. INTRODUCTION
Titanium dioxide (TiO2) is a widely used catalytic material due to its excellent stability and physical–chemical properties. It has demonstrated a wide range of application potentials in hydrogen production, lithium-ion batteries, fuel cells, gas sensors, detoxification, photovoltaic, photocatalysts, and supercapacitors.1–13 The one-dimensional (1D) morphology, such as TiO2 nanowire (NW), is considered as a superior candidate for achieving higher performance in those applications compared to the bulk form. For example, a TiO2 NW-based electrode can provide large surface area for effectively collecting photons and/or electrons.4 The high crystal quality of the NWs is essential for reducing the scattering effect and hence improving the electron mobility. In addition, using TiO2 NWs as electrodes could be beneficial to the mechanical stability of the device.2,4 Typically, TiO2 exhibits three different polymorphs (anatase, brookite, and rutile), which have different properties and result in different performance. Therefore, to synthesize TiO2 NWs with defined phase, shape, dimension, and high quality, crystallinity is of fundamental importance for achieving desired functionality and performance. Nonetheless, a well-controlled growth of TiO2 NW is rather challenging due to the existence of multiple polymorphs and the thermodynamically unfavorable a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2012.356 270
J. Mater. Res., Vol. 28, No. 3, Feb 14, 2013
http://journals.cambridge.org
Downloaded: 24 Mar 2015
crystallography for anisotropic crystal growth.14,15 Templated sol–gel method, hydrothermal synthesis, and electro
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