Thin films with Switchable Conductivity: About the Production of Vanadium Oxide thin Films Applying CVD Technique

Oxides of vanadium are widely used in catalytic protocols for pollution abatement

[1, 2] synthetic fuel production [3, 4] and heterogeneous catalysis in general. In addition, Vanadium dioxide has some peculiar properties: Vanadium dioxides exhibits a phase transition from semi-conductor to a metal at 68 °C. This process is called Mott transition [5] and occurs due to change in the unit cell structure from monoclinic structure to tetragonal rutile structure. These unusual properties could be used as thermo-electric switches, optical switches, thermal windows and super-capacitors. Vanadium dioxides films were grown in hot wall, horizontal, low pressure MOCVD apparatus. The CVD fabrication of 1-3 µm thick VO₂ films employed sublimation of Vanadyl acetylacetonate (VO(acac)₂) at ~150-190^oC and its subsequent reaction with O₂ at CVD chamber. Annealing of VO₂ films under oxidizing environment will result in V₂O₅ films [6]. The dependence of film morphology and resistance properties on CVD reactor temperature, precursor sublimation temperature and the substrate position along the reaction axis was tested. Scanning Electron Microscopy (SEM) analysis reveals grain sizes in the range of 0.5-2 µm. Four probe resistance measurements indicate resistance drop of 3-4 orders of magnitude across the insulator-to-metal transition. Scattering experiments are a method to explore the energy conversion of excited molecules on surfaces. These processes are essential for the understanding of macroscopic catalytic reactions.Scattering of gas molecules from insulator and from metal surface are well established [7]. The motivation of this project is to perform scattering experiments from surfaces with switchable conductivity and work function. Here presented preliminary results of NO molecule scattering from the resulting VO₂ thin films.

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