Finite-size effect on the first-order metal-insulator transition inVO2films grown by metal-organic chemical-vapor deposition

Abstract

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.

Thin films of VO2 on glass by atomic layer deposition: microstructure and electrical properties

“…Several thin film deposition techniques including sputtering [6,7], evaporation [4,8], pulsed laser deposition [9], and chemical methods such as spray pyrolysis and CVD [10,11] have been used to prepare thin films of VO 2 on different substrates. It has been reported that highly oriented VO 2 thin films deposited on single crystal substrates by different techniques display excellent characteristics such as a large change in resistivity at the transition temperature (by a factor of $2 Â 10 4 ) and a small hysteresis in the transition temperature ($11C) [6,11]. However, films deposited on glass substrates have not displayed similarly sharp changes at the S-M phase transition [12][13][14].…”

Thermochromic Properties of VO2-PVP Composite Coatings

“…Due to the small compositional differences between the numerous phases of vanadium oxide, hence VO 2 preparation requires a stringently controlled process that provides the desired oxygen stoichiometry and correct crystalline structure. VO 2 films have been successfully synthesized by a number of methods (physical and chemical), including DC and RF reactive magnetron sputtering [42][43][44][45][46][47], reactive ion-beam sputtering [48][49][50][51][52], reactive evaporation [53,54], chemical vapor deposition [55][56][57], pulsed laser deposition (PLD) [58][59][60][61][62], electrochemical (anodic) oxidation [63,64] and sol-gel processes [65][66][67]. Given the requirement for accurate optimization to obtain the correct VO 2 polycrystalline structure, and due to the numerous electronic valences of vanadium and its high affinity for oxygen, it is challenging to produce large thermochromic VO 2 thin dddfilms using such techniques.…”

A micromachined thermo-optical light modulator based on the VO 2 phase transition

“…A wide range of deposition methods has been investigated to fabricate VO 2 thin films, including reactive sputtering [12], reactive evaporation [13], chemical vapor deposition [14], pulsed laser ablation [15], as well as sol-gel methods [16]. In this study, VO 2 thin film was fabricated by e-beam evaporation of vanadium film followed by thermal oxidation into vanadium oxide in oxygen ambient.…”