Pulsed laser deposition of oriented V 2 O 5 thin films
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Eli Mateeva and Dennis W. Readey Colorado School of Mines, 1500 Illinois St., Golden, Colorado 80401 (Received 6 March 2000; accepted 4 August 2000)
We have found that by varying only the substrate temperature and oxygen pressure five different crystallographic orientations of V2O5 thin films can be grown, ranging from amorphous to highly textured crystalline. Dense, phase-pure V2O5 thin films were grown on SnO2/glass substrates and amorphous quartz substrates by pulsed laser deposition over a wide range of temperatures and oxygen pressures. The films’ microstructure, crystallinity, and texturing were characterized by electron microscopy, x-ray diffraction, and Raman spectroscopy. Temperature and oxygen pressure appeared to play more significant roles in the resulting crystallographic texture than did the choice of substrate. A growth map summarizes the results and delineates the temperature and O2 pressure window for growing dense, uniform, phase-pure V2O5 films.
I. INTRODUCTION
V2O5 has been studied and applied in many diverse applications including catalysts, sensors, electrochromic windows, and rechargeable battery electrodes. Increasingly, thin films are gaining in importance for industrially useful applications as device sizes are reduced or device volumes and weights are minimized. Such applications include power sources for computer chips and microsensors. Other applications include real-estatesaving applications, such as batteries integrated into space module panels or combined photovoltaic/ rechargeable battery devices. In rechargeable batteries with V2O5 electrodes, V2O5 is most often the cathode. Recently, however, two all solid-state batteries have been fabricated in which both the anode and cathode are amorphous V2O5.1,2 Electrochromic devices, with applications in such technologies as sunroofs, rearview mirrors, and smart windows, have been fabricated with amorphous V2O5 acting as the counter-electrode to WO3.3 For the three thin-film devices just mentioned, three different methods were used to deposit the V2O5 layers. V2O5 thin films have been deposited by many methods including sputtering,1,4–7 electron-beam evaporation,8 flash evaporation,9 thermal evaporation,10 plasma-enhanced chemical vapor deposition,11 sol-gel,12–17 dip coating,18 anodic deposition,19,20 and pulsed laser deposition (PLD).21 Many different materials have been deposited by PLD, the method used in this work.22 PLD is a nonequilibrium
process in which a laser beam strikes a target, ablating a plume of material that evolves normal to the target and deposits on a substrate.22 The target stoichiometry is generally transferred to the film; however, reactive ablation also can be accomplished by ablating in a reactive atmosphere of, for example, O2 or forming gas. Films can be dense, sometimes greater than 90% of the single-crystal density. Textured and epitaxial films can often be grown by PLD with no postdeposition anneal. In some cases, the film texture can be controlled by modifying the substrate, the substrate temperature, TS,
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