Optical nonlinearities of nanostructured VO₂ thin films with low phase transition temperature

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• 作者：Boqing Wang ; Sihai Chen ; ^{cshai99@163.com} ; Zhangli Huang ; Ming Fu
• 关键词：VO2 thin film ; Low phase transition temperature ; Nonlinearity ; Ultrafast
• 刊名：Applied Surface Science
• 出版年：2012
• 期刊代码：6_01694332
• 类别：ms
• 出版时间：1 May, 2012
• 卷：258
• 期：14
• 页码：5319-5322
• 文件大小：666 K

摘要

Vanadium dioxides (VO₂) thin films which change from a monoclinic semiconductor phase to a tetragonal metallic structure at the temperature of 29 掳C have been fabricated by reactive ion beam sputtering. Micrograph of scanning electron microscope (SEM) shows that the grain size of VO₂ crystallite ranges from 20 nm to 50 nm. Regeneratively amplified Ti:sapphire laser pulses were applied to induce the phase transition, which was accompanying with the third-order optical nonlinearities in VO₂ thin films. Open-aperture and closed-aperture measurements of Z-scan were used to study the optical absorptive and refractive nonlinearities. Nanostructured VO₂ thin films exhibit two-photon absorption and a negative nonlinear index of refraction when phase transition is induced. The optical nonlinearities are due to excitation of electronic subsystem only and without involving of the structural semiconductor-to-metal phase transition.