Single-crystalline epitaxy and twinned structure of vanadium dioxide thin film on (0001) sapphire

VO2 thin films prepared by pulsed-laser ablation have been investigated by high-resolution x-ray diffraction, x-ray pole-figure, Rutherford backscattering/channelling and electrical measurements. The results show that VO2 films deposited on (0001) sapphire substrates grow with well determined orientations in the plane: VO2 [100] parallel to sapphire [11 (2) over bar 0] and out of the plane: (010) VO2 parallel to (0001) sapphire. The aligned-to-random ratio of backscattered yield of the spectra (chi(min)) can be as low as 5%, and the electrical resistivity changes by a factor of 6 x 10(4) during the phase transformation with a hysteresis loop width of 0.9 degrees C, which implies that both the structure and the properties of the him are very close to those of bulk single-crystal VO2. The (010)-oriented VO2 him 'prefers' to form twinned structure with 120 degrees domain walls. Molybdenum substitutional doping up to the level of 1.5 at.% does not degrade the crystal quality.