VO2 thin films with thicknesses from 100 to 2 nm were prepared on C-plane sapphire (0001) substrates by magnetron sputtering and remarkable thickness-dependent structural and optical properties were found. Below 10 nm, the films are nonconductive, island structured, and their phase transition temperatures are reduced to be much lower than those of the continuous, thick films. Structural defects in the island crystal films may be one of the main reasons for this temperature reduction. The film growth mode was identified to be the Vollmer-Weber (island growth)-type in the initial stage.
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