Linear Interplay Between Raman Shift and Laser Irradiation in Photothermal-Strained Monoclinic Vanadium Dioxide.

Vanadium dioxide as a strongly correlated electron material undergoes metal-insulator phase transitions and ferroelastic domain switching which highly couple to local strain distribution. Understanding the mechanisms and achieving the modulations require precise and high-resolution characterization of strain in vanadium dioxide. Micro-Raman spectroscopy is widely used to nondestructively characterize the strain on the surface of materials. However, vanadium dioxide is sensitive to multi-fields and with multiple physical properties correlated. It is vital and challenging to uncouple the multiple responses of vanadium dioxide to micro-Raman spectroscopy and achieve precise characterization of strain distribution. Herein, a linear relation between Raman shift and laser irradiation is revealed, which is originated from photothermal strain in monoclinic vanadium dioxide. By linear fitting and extrapolation, the strain-dependent coefficient is obtained for drifting of Raman shift and the intrinsic Raman shift without strain or laser irradiation, which enables to precisely characterize the strain distribution in vanadium dioxide.