Raman Spectroscopy of Carbon Nanotubes under Axial Strain: Raman Spectroscopy of Carbon Nanotubes under Axial Strain and Surface-Enhanced Raman Spectroscopy of Individual Carbon Nanotubes

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Resonant Raman spectroscopy of individual carbon nanotube bundles under axial strains up to 17% are presented. This strain causes nanotube debundling which gives insight into the nature of the broad metallic G- band. For metallic nanotubes, the G- band upshifts and narrows with strain, making it appear more semiconductor-like. This metal to semiconductor transition is irreversible with strain, indicating that nanotube-nanotube coupling plays a significant role in the observed G- band of metallic nanotubes. The vibrational and electronic properties of these nanotubes under strain are modeled using tight-binding calculations. A systematic study of surface enhanced Raman spectroscopy (SERS) of carbon nanotubes. Raman spectra of individual carbon nanotubes are measured before and after depositing silver nanoparticles. Regions exhibiting SERS enhancement were located relative to a grid, allowing subsequent scanning electron microscopy to be performed. SERS enhancement factors up to 134,000, a consistent upshift in the G band Raman frequency and nanoparticle heating in excess of 600°C are revealed.

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Enhanced Field Emission from Metallic Surfaces and Nanowires

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The role of material properties, surface preparation and cleaning techniques on Nb and Cu was studied for EFE , which is disastrous for high field vacuum devices. Dry ice cleaning is found to suppress EFE from the metallic surfaces very efficiently. High purity single crystal and large grain Nb samples showed the onset of FE at high fields (120 ? 200 MV/m).For the first time, the grain boundary assisted field emission was observed for Nb. A correlationbetween size of emitters and onset fields is obtained, which sets a threshold for the tolerable defect size to achieve the envisaged accelerating gradients in cavities reliably.Additionaly, the systematic study performed on electrochemically deposited Cu, Ni and Au nanowires of different aspect ratios and spatial distribution for cold cathode applications. In our findings, Au coating on Ni nanowires provided improved FE properties. Further, in Au Nanowires up to 40 % percentage of the wires were emitting. Achieving much larger emitter number densities ~10^5 cm^?2 at 6 V/µm compared to CNT cathodes with respect to the number of deposited nanostructures, makes Au NWs interesting for cold cathode applications.

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