Role of Vanadyl Oxygen in Understanding Metallic Behavior of V₂O₅(001) Nanorods

Vanadium pentoxide (V₂O₅), the most stable member of vanadium oxide family, exhibits interesting semiconductor to metal transition in the temperature range of 530–560 K. The metallic behavior originates because of the reduction of V₂O₅ through oxygen vacancies. In the present report, V₂O₅ nanorods in the orthorhombic phase with crystal orientation of (001) are grown using vapor transport process. Among three nonequivalent oxygen atoms in a VO₅ pyramidal formula unit in V₂O₅ structure, the role of terminal vanadyl oxygen (O_I) in the formation of metallic phase above the transition temperature is established from the temperature-dependent Raman spectroscopic studies. The origin of the metallic behavior of V₂O₅ is also understood due to the breakdown of pdπ bond between O_I and nearest V atom instigated by the formation of vanadyl O_I vacancy, confirmed from the downward shift of the bottom most split-off conduction bands in the material with increasing temperature

Low-wettable Nanopatterned SERS Platform for Sub-ppt-level Detection of Xanthene Food Additive

Surface-enhanced Raman spectroscopy (SERS) is a label-free analytical technique for real-time trace-level detection. In this study, we report the formation of a monolayer SERS substrate of gold nanorods (GNRs) to detect hazardous and nonpermitted xanthene food additive dye, Rose Bengal (RB). The optimized aspect ratio of GNRs produced by a novel method is found to be an excellent candidate for the SERS substrate. Moreover, we demonstrate that a low wettability of nanometer-scale smooth (Rrms ∼0.3 nm) substrate allows a tip–tip large-area assembly of GNRs. The electromagnetic field enhancement by the assembled GNRs is further revealed by the finite-difference time-domain calculation, which enables 0.1 pM detection of RB in an aqueous medium with an analytical enhancement factor of ∼1010. The large-area homogeneity of the SERS substrate is established through Raman imaging with a standard deviation of ∼9.15%. The practical viability of the substrate is also upheld by ppb-level detection of RB in a commercial brown product

Probing Localized Surface Plasmons of Trisoctahedral Gold Nanocrystals for Surface Enhanced Raman Scattering

Trisoctahedral (TOH) shaped gold (Au) nanocrystals (NCs) have emerged as a new class of metal nanoparticles (MNPs) due to their superior catalytic and surface enhanced Raman scattering (SERS) activities caused by the presence of high density of atomic steps and dangling bonds on their high-index facets. We examine the radiative localized surface plasmon resonance (LSPR) modes of an isolated single TOH Au NC using cathodoluminescence (CL), with high resolution spatial information on the local density of optical states (LDOS) across the visible spectral range. Further, we show pronounced enhancement in the Raman scattering by performing Raman spectroscopic measurements on Rhodamine 6G (R6G)-covered TOH Au NPs aggregates on a Si substrate. We believe that the hot spots between two adjacent MNP surfaces (“nanogaps”) can be significantly stronger than single particle LSPRs. Such “nanogaps” hot spots may have crucial role on the substantial SERS enhancement observed in this report. Consequently, the present study indicates that MNPs aggregates are highly desirable than individual plasmonic nanoparticles for possible applications in SERS based biosensing