We studied the finite-size efFect on the first-order metal-insulator phase transition and the accompanying tetragonal-to-monoclinic structural transition of VO2 films. The VO2 films were epitaxially grown by a metal-organic chemical-vapor-deposition technique on the (101) growth plane of a 125-A-thick Ti02 buffer layer which was also epitaxially predeposited on polished sapphire (1120) substrates. The thickness of the VO2 films in this study ranges from 60 to 310 A. We find that VO2 films grow isomorphically on the Ti02 bufFer layer resulting in a high degree of epitaxial VO2 films.We determined structural correlation lengths of the VO2 films parallel and normal to the growth plane from the x-ray-diÃraction widths of VO2 reflections at room temperature.The structural order parameter associated with the monoclinic distortion and the change in resistivity associated with the metal-insulator phase transition were simultaneously measured using x-ray-diKraction and resistivity measurements. It was found that the transition temperature, width of the transition, and the estimated electronic gap are dependent on the structural correlation length normal to the growth plane. These dependences are discussed in terms of finite-size and substrate efFects on the first-order phase transition.
We performed in-situ x-ray reflectivity measurements to study the growth dynamics of gold sputter deposited onto silicon using an x-ray scattering chamber equipped with a faced magnetron source where the substrate is held at a right angle relative to the sputtering guns. By operating the guns at low power (I watt) and under 20 mTorr Ar, we could control the gold deposition rate to less than IA/sec. The observed x-ray reflectivity for gold deposited onto a silicon substrate at 300 K and 400 K is consistent with nucleated island growth for average gold particle sizes less than 50 A. Above 50 A, the reflectivity data indicates that the gold film uniformly covers the silicon surface, and that as the film thickness is increased the gold-vacuum interface gets progressively rougher. Detailed analysis of room temperature data is in progress, as is the temperature dependence on the roughness of the gold vacuum interface.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.