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Phase-selective growth of VO2 and V2O5 nanowires was realized via catalyst-free physical vapor deposition from bulk VO2 powder. Single nanowire Raman spectroscopy was used to analyze the distribution of the vanadium oxide phases within the reactor. VO2 (V2O5) nanowires were identified by characteristic peaks at 197, 224, and 620 cm-1 (149, 700, and 994 cm-1). Electron diffraction and polarization-dependent Raman spectra indicated that the growth directions of VO2 and V2O5 nanowires were [100] and [010]. Analysis of Raman spectra in two polarization configurations is sufficient to distinguish between low-index nanowire growth directions for the V2O5 phase. Single nanostructure Raman measurements thus provide a means to rapidly analyze the phase and growth direction of anisotropic nanostructures. [ABSTRACT FROM AUTHOR]

Real-time spectroscopy provides invaluable information about the evolution of dynamical processes, especially non-repetitive phenomena. Unfortunately, the continuous acquisition of rapidly varying spectra represents an extremely difficult challenge. One method, wavelength–time mapping, chirps the spectrum so that it can be measured using a single-shot oscilloscope. Here, we demonstrate a method that overcomes a fundamental problem that has previously plagued wavelength–time spectroscopy: fine spectral resolution requires large dispersion, which is accompanied by extreme optical loss. The present technique uses an optically amplified wavelength–time transformation to beat the dispersion-loss trade-off and facilitate high-resolution, broadband, real-time applications. We show that this distributed amplification process can even be pumped by broadband noise, generating a wide gain bandwidth using a single pump source. We apply these techniques to demonstrate real-time stimulated Raman spectroscopy. Amplified wavelength–time Raman spectroscopy creates new opportunities for the study of chemical and physical dynamics in real time. [ABSTRACT FROM AUTHOR]