We report catalyst-free direct synthesis of vertical graphene nanosheets (VGNs) on SiO2/Si and quartz substrates using microwave electron cyclotron resonance - plasma enhanced chemical vapor deposition. The evolution of VGNs is studied systematically at different growth stages. Raman analysis as a function of growth time reveals that two different disorder-induced competing mechanisms contributing to the defect band intensity. The VGNs grown on SiO2/Si substrates predominantly consists of both vacancy-like and hopping defects. On the other hand, the VGNs grown on quartz substrates contain mainly boundary-like defects. XPS studies also corroborate Raman analysis in terms of defect density and vacancy-like defects for the VGNs grown on SiO2/Si substrates. Moreover, the grown VGNs exhibit a high optical transmittance from 95 to 78 % at 550 nm and the sheet resistance varies from 30 to 2.17 kohms/square depending on growth time.Comment: 19 pages, 8 figures, 1 table; Accepted in Journal of Raman Spectroscopy (2014

We report, for the first time, the luminescence property of the hydroxyl group surface functionalized quantum dots (QDs) and nanoparticles (NPs) of SnO2 using low energy excitations of 2.54 eV (488 nm) and 2.42 eV (514.5 nm). This luminescence is in addition to generally observed luminescence from 'O' defects. The as-prepared SnO2 QDs are annealed at different temperatures under ambient conditions to create NPs with varying sizes. Subsequently, the average size of the NPs is calculated from the acoustic vibrations observed at low frequencies in the Raman spectra and by the transmission electron microscopy measurements. Detailed photoluminescence studies with 3.815 eV (325 nm) excitation reveal the nature of in-plane and bridging 'O' vacancies as well as adsorption and desorption occurring at different annealing temperatures. X-ray photoelectron spectroscopy studies also support this observation. The defect level related to the surface -OH functional groups shows a broad luminescence peak at around 1.96 eV in SnO2 NPs which is elaborated using temperature dependent studies.

The flow field created by two impinging liquid jets in a cylindrical chamber is investigated using particle tracing, laser Doppler anemometry, and three-dimensional numerical simulation. The jet Reynolds number (based on the mean jet velocity and diameter) range is from 50–300. Results show that there is a threshold value of the Reynolds number beyond which the flow exhibits oscillations. Computer simulations agree well with the experimental visualizations, for both the overall observed flow pattern and a quantitative measure of the oscillations.

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Role of 'O' defects in sensing pollutant with nanostructured SnO 2 is not well understood, especially at low temperatures. SnO 2 nanoparticles were grown by soft chemistry route followed by subsequent annealing treatment under specific conditions. Nanowires were grown by chemical vapor deposition technique. A systematic photoluminescence (PL) investigation of 'O' defects in SnO 2 nanostructures revealed a strong correlation between shallow donors created by the in-plane and the bridging 'O' vacancies and gas sensing at low temperatures. These SnO 2 nanostructures detected methane (CH 4 ), a reducing and green house gas at a low temperature of 50 °C.Response of CH 4 was found to be strongly dependent on surface defect in comparison to surface to volume ratio. Control over 'O' vacancies during the synthesis of SnO 2 nanomaterials, as supported by X-ray photoelectron spectroscopy and subsequent elucidation for low temperature sensing are demonstrated.