Sharpened VO2 Phase Transition via Controlled Release of Epitaxial Strain

5 years ago

Sharpened VO2 Phase Transition via Controlled Release of Epitaxial Strain

Weidong Zhou, Zhenqiang Ma, Bongwook Chung, Shih-Chia Liu, Kyung Song, Yanjun Ma, Si-Young Choi, Sang June Cho, Fei Xue, Daesu Lee, Chang-Beom Eom, Sang Ho Oh, Wenjuan Fan, Jaeseong Lee, Jaichan Lee, Dong Liu, Long-Qing Chen, Jacob Podkaminer

Phase transitions in correlated materials can be manipulated at the nanoscale to yield emergent functional properties, promising new paradigms for nanoelectronics and nanophotonics. Vanadium dioxide (VO₂), an archetypal correlated material, exhibits a metal–insulator transition (MIT) above room temperature. At the thicknesses required for heterostructure applications, such as an optical modulator discussed here, the strain state of VO₂ largely determines the MIT dynamics critical to the device performance. We develop an approach to control the MIT dynamics in epitaxial VO₂ films by employing an intermediate template layer with large lattice mismatch to relieve the interfacial lattice constraints, contrary to conventional thin film epitaxy that favors lattice match between the substrate and the growing film. A combination of phase-field simulation, in situ real-time nanoscale imaging, and electrical measurements reveals robust undisturbed MIT dynamics even at preexisting structural domain boundaries and significantly sharpened MIT in the templated VO₂ films. Utilizing the sharp MIT, we demonstrate a fast, electrically switchable optical waveguide. This study offers unconventional design principles for heteroepitaxial correlated materials, as well as novel insight into their nanoscale phase transitions.

Publisher URL: http://dx.doi.org/10.1021/acs.nanolett.7b02482

DOI: 10.1021/acs.nanolett.7b02482