Correlation between Growth Conditions, Microstructure, and Optical Properties in Pulsed-Laser-Deposited V 2 O 5 Thin Films C. V. Ramana,* ,†,§ R. J. Smith, † O. M. Hussain, ‡ C. C. Chusuei, § and C. M. Julien | Surface Science/Ion Beam Laboratory, Department of Physics, Montana State UniVersity, Bozeman, Montana 59717, Thin Film Laboratory, Department of Physics, Sri Venkateswara UniVersity, Tirupati -517 502, India, Department of Chemistry, UniVersity of Missouri-Rolla, Rolla, Missouri 65409, and Laboratoire des Milieux Desordonnes et Heterogenes, UniVersite Pierre et Marie Curie, 4 place Jussieu, 75252 Paris Cedex 05, France ReceiVed September 3, 2004. ReVised Manuscript ReceiVed December 13, 2004 V 2 O 5 thin films were prepared by pulsed laser deposition (PLD) over a wide substrate temperature range, 30-500 °C, and were characterized by studying their microstructure and optical properties. Rutherford backscattering spectrometry (RBS), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and UV-vis-NIR spectral measurements were made on the PLD V 2 O 5 films to understand the effect of substrate temperature on the chemical composition, elemental distribution, surface morphology, and optical properties. The substrate temperature strongly influences the structure and optical properties of PLD V 2 O 5 films and a correlation exists between the growth conditions, grain structure, and optical characteristics. The grain size increased, associated with a change in surface morphology, with increasing substrate temperature. The optical energy band gap of PLD V 2 O 5 films is strongly dependent on the substrate temperature and decreased from 2.47 to 2.12 eV with the increase in temperature from 30 to 500 °C. I. Introduction There has been tremendous interest in transition-metal oxide thin films for a wide range of applications in microelectronics, optoelectronics, and solid-state ionics. 1,2 Vanadium pentoxide (V 2 O 5 ) has been widely studied in recent years in view of its novel material characteristics, which can be readily integrated into many scientific and technological applications. V 2 O 5 has high potential for the development of electrochromic devices, electronic informa- tion displays, and color memory devices. 2-5 The ability to incorporate large amounts of lithium ions coupled with its peculiar optical properties ranks vanadium oxides among the most studied materials for electrochemical applications in general, and in particular for applications in high-energy density solid-state batteries and information displays. 5-7 The variable optical properties of V 2 O 5 films find application in the development of smart windows. 7 V 2 O 5 films can also be integrated in other technological applications where the typical functions of these films include chemical sensing, photochromism, catalysis, and optical and electrical switch- ing. 8-11 One of the major problems encountered during the preparation of vanadium oxides in thin-film form is tuning the process parameters for controlled growth and desired properties because the window of processing over which these oxides occur as a stable single-phase material is relatively small. Vanadium forms a large number of oxides each of which is stable over a certain composition range. Particularly, oxides in the V 2 O 5 -V 2 O 3 system are complex and many intermediate oxide phases exist within this compositional range. 8 The composition and phase stability of grown films is highly important for all practical applica- tions. V 2 O 5 films can be obtained by thermal evaporation, 10 flash evaporation, 12 electron-beam evaporation, 13 sol-gel growth methods, 2,14 chemical vapor deposition, 15,16 and sputtering. 7,8 The removal of oxygen from the V 2 O 5 lattice, when heated above its melting point in a vacuum or a reducing atmosphere, causes the formation of defects or reduced phases, which could eventually lead to the fading or poor electrochromic/electrochemical performance. 8,13 * Corresponding author. 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