Journal
JOURNAL OF OPTICS A-PURE AND APPLIED OPTICS
Volume 11, Issue 12, Pages -Publisher
IOP PUBLISHING LTD
DOI: 10.1088/1464-4258/11/12/125002
Keywords
surface-enhanced Raman scattering (SERS); phase transition; hysteresis; size effects; Mie theory; vanadium dioxide (VO2); gold (Au); hybrid nanoparticles; Au-VO2
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Funding
- United States Department of Energy, Office of Science [DE-FG02-01ER45916]
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We report the first experimental application of surface-enhanced Raman scattering (SERS) to the study of the structural phase transition of vanadium dioxide (VO2). Using arrays of gold-capped VO2 nanoparticles (Au + VO2 NPs) and a VO2 film covered with Au islands, we obtained the temperature evolution of the SERS intensity with respect to the amount of accessible material across the monoclinic-tetragonal-monoclinic transformation cycle of VO2. The smallest Au + VO2 NPs displayed the largest deviations from the bulk transition temperatures to complete the transformation, resulting in the widest thermal hysteresis, while the Au + VO2 film exhibited the narrowest hysteresis. The observed size dependence agrees qualitatively with the model of defect-induced nucleation of the VO2 transition, although the magnitude of the hysteresis width and its dependence on NP size were less pronounced than those in a previous study of elastic light scattering from bare VO2 NPs. The discrepancies may stem from the creation of extrinsic nucleation sites in the VO2 NPs during their high-temperature processing in the presence of the Au caps; alternatively, the hystereses of the structural and electronic transitions could each have a different dependence on size. Lastly, we correlate the size dependence of the VO2 SERS intensity with the scattering efficiency of the Au nanoparticles, within the framework of a modified Mie-theory calculation.
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