Ambiguous Role of Growth-Induced Defects on the Semiconductor-to-Metal Characteristics in Epitaxial VO2/TiO2 Thin Films

Cristian N Mihailescu; Elli Symeou; Efthymios Svoukis; Raluca F Negrea; Corneliu Ghica; Valentin Teodorescu; Liviu C Tanase; Catalin Negrila; John Giapintzakis

doi:10.1021/acsami.8b01436

Ambiguous Role of Growth-Induced Defects on the Semiconductor-to-Metal Characteristics in Epitaxial VO₂/TiO₂ Thin Films

ACS Appl Mater Interfaces. 2018 Apr 25;10(16):14132-14144. doi: 10.1021/acsami.8b01436. Epub 2018 Apr 10.

Authors

Cristian N Mihailescu^{1

2}, Elli Symeou¹, Efthymios Svoukis¹, Raluca F Negrea³, Corneliu Ghica³, Valentin Teodorescu³, Liviu C Tanase³, Catalin Negrila³, John Giapintzakis¹

Affiliations

¹ Department of Mechanical and Manufacturing Engineering , University of Cyprus , 75 Kallipoleos Avenue , PO Box 20537, 1678 Nicosia , Cyprus.
² National Institute for Laser , Plasma and Radiation Physics , 409 Atomistilor Street , PO Box MG-36, 077125 Magurele , Romania.
³ National Institute of Materials Physics , RO-077125 Magurele , Romania.

PMID: 29595950
DOI: 10.1021/acsami.8b01436

Abstract

Controlling the semiconductor-to-metal transition temperature in epitaxial VO₂ thin films remains an unresolved question both at the fundamental as well as the application level. Within the scope of this work, the effects of growth temperature on the structure, chemical composition, interface coherency and electrical characteristics of rutile VO₂ epitaxial thin films grown on TiO₂ substrates are investigated. It is hereby deduced that the transition temperature is lower than the bulk value of 340 K. However, it is found to approach this value as a function of increased growth temperature even though it is accompanied by a contraction along the V⁴⁺-V⁴⁺ bond direction, the crystallographic c-axis lattice parameter. Additionally, it is demonstrated that films grown at low substrate temperatures exhibit a relaxed state and a strongly reduced transition temperature. It is suggested that, besides thermal and epitaxial strain, growth-induced defects may strongly affect the electronic phase transition. The results of this work reveal the difficulty in extracting the intrinsic material response to strain, when the exact contribution of all strain sources cannot be effectively determined. The findings also bear implications on the limitations in obtaining the recently predicted novel semi-Dirac point phase in VO₂/TiO₂ multilayer structures.

Keywords: growth of VO2 films on TiO2; interdiffusion between film and substrate; pulsed laser deposition; semiconductor-metal phase transition; thermal and epitaxial strain; thin film epitaxy.