Size, composition and alignment of VO2 microrod crystals by the reduction of V2O5 thin films, and their optical properties through insulator-metal transitions.

VO 2 microrods (MRs) have been successfully synthesized by the reduction of V 2 O 5 thin films. The effects of reduction temperature and thickness of the precursor V 2 O 5 thin films on the stochiometry and morphology of the resulting VO 2 MRs have been studied in this work. Results show that size of the VO 2 MRs increases with increasing precursor thickness due to the enlargement of the droplets during the melting of V 2 O 5 thin films. Further, the growth of VO 2 MRs from V 2 O 5 droplets on a sapphire substrate form a unique angle between each other, which is probably due to epitaxial growth. Reduction temperatures between 600 °C and 650 °C are preferred for the growth of VO 2 MRs, while temperatures lower or higher than this range produce V 2 O 5 nanostructures or VO 2 nanoparticles, respectively. HRTEM shows that during VO 2 MR's growth, the (110) plane remains parallel to the Si substrate, and a 10 nm amorphous interface was formed between the VO 2 MR and the Si substrate. Optical properties of the MRs were examined by carrying out light scattering experiments as a function of temperature to identify the temperature range of insulator-to-metal (IM) and metal-to-insulator (MI) transition characteristics. The optical scattering experiments show the large influence of microrod (MR) size and distribution on the characteristics of MI and IM transitions. The transition behavior can range from polycrystalline film type transition to new unique features. Image 1 • The size of the VO 2 microrods has been successfully controlled by the precursor V 2 O 5 film thickness. • Temperature range for producing VO 2 microrods was found to be between 600 °C and 650 °C. • Microrods growth is aligned along two directions on the sapphire crystal surface. • Optical properties have been studied by light scattering through metal-insulator transition (MIT). • The MIT characteristics depend on the microrod size and distribution, and exhibits memory-like behavior during cooling. [ABSTRACT FROM AUTHOR]