Strain Effects in Epitaxial VO2 Thin Films on Columnar Buffer-Layer TiO2/Al2O3 Virtual Substrates

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• 作者：Eric Breckenfeld ; Heungsoo KimKatherine Burgess ; Nicholas Charipar ; Shu-Fan Cheng ; Rhonda Stroud ; Alberto Piqué
• 刊名：ACS Applied Materials & Interfaces
• 出版年：2017
• 出版时间：January 18, 2017
• 年：2017
• 卷：9
• 期：2
• 页码：1577-1584
• 全文大小：530K
• ISSN：1944-8252

文摘

Epitaxial VO<sub>2sub>/TiO<sub>2sub> thin film heterostructures were grown on (100) (m-cut) Al<sub>2sub>O<sub>3sub> substrates via pulsed laser deposition. We have demonstrated the ability to reduce the semiconductor–metal transition (SMT) temperature of VO<sub>2sub> to ∼44 °C while retaining a 4 order of magnitude SMT using the TiO<sub>2sub> buffer layer. A combination of electrical transport and X-ray diffraction reciprocal space mapping studies help examine the specific strain states of VO<sub>2sub>/TiO<sub>2sub>/Al<sub>2sub>O<sub>3sub> heterostructures as a function of TiO<sub>2sub> film growth temperatures. Atomic force microscopy and transmission electron microscopy analyses show that the columnar microstructure present in TiO<sub>2sub> buffer films is responsible for the partially strained VO<sub>2sub> film behavior and subsequently favorable transport characteristics with a lower SMT temperature. Such findings are of crucial importance for both the technological implementation of the VO<sub>2sub> system, where reduction of its SMT temperature is widely sought, as well as the broader complex oxide community, where greater understanding of the evolution of microstructure, strain, and functional properties is a high priority.