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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.

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.

There is a great impetus in the research on semiconductorbased nanostructures due to their unusual optoelectronic properties that result from quantum size effects.[1] The recent success of silicon-based nanostructures [2±6] with interesting optical [7,8] and electronic [9] properties has renewed interest in this relevant field of study. Exotic structures of silicon-based nanowires with self-organized silicon nanospheres have also been reported [10] furthering the ªbottom±upº paradigm for device fabrication. The formation of silicon-based nanowhiskers, following the vapor±liquid±solid (VLS) growth mechanism and using a metal catalyst has been described in all these reports.[2±10] Metals play a major role in the catalytic action, and a detailed study of the metal±silicon interaction is a subject of considerable interest [11] with regard to both fundamental studies and technological applications. However, except for the formation of CoSi 2 /Si and NiSi 2 /Si nanocomposites, and possible implications in the electrical contact formation for silicon nanowhiskers, [4] very little attention has been given to the possible manifestations of the metal±silicon interaction during the growth of nanowires. Gold is the most widely used catalyst in the VLS growth of silicon-based nanowhiskers, as the Au±Si system is a simple eutectic with the eutectic point at 363 C at about 19 at.-% silicon. [12] Over the last three decades, the Au±Si system has been the most well-studied system, with research concentrating o its possible applications in microelectronic devices. Different metastable phases within the composition ranges of Au 2 Si to Au 7 Si, with different structural and electronic properties, have been reported. [12] Despite the early setback of metallization with gold in silicon, as the device property is degraded by a high diffusion rate of gold in silicon, it still has an advantage in bipolar and radio frequency power transistors, as well as for chip capacitors used for internal matching.[13]We report here the growth and optical properties of a unique structure comprised of silicon-based nanowires with self-assembled gold silicide nanospheres embedded in it. High-resolution transmission electron microscopy (HRTEM), along with analytical electron microscopic (AEM) analyses and selected-area electron diffraction (SAED) studies have been used to characterize the nanowire and the pea-podded nanoclusters. Morphological studies aiding the description of the growth mechanism have been performed using field emission scanning electron microscopy (FESEM). The optical photoluminescence (PL) properties of the noble silicon-based nanowire were studied using the 532 nm line of a Nd:YAG laser in the backscattering configuration of a micro-PL setup.A morphological study showed (Fig. 1a) a noble type of one-dimensional nanocomposite with nanocrystals of mostly spherical (5±30 nm), and a few cylindrical, shapes embedded in the nanowires. These nanocomposites were obtained by thermal annealing of gold/amorphous-silicon (Au/a-Si) bilayers at 1...

forbidden modes and surface defect-related Raman features in SnO 2 nanostructures carry information about disorder and surface defects which strongly influence important technological applications like catalysis and sensing. Because of the weak intensities of these peaks, it is difficult to identify these features by using conventional Raman spectroscopy. Tip enhanced Raman spectroscopy (TERS) studies conducted on SnO 2 nanoparticles (NPs) of size 4 and 25 nm have offered significant insights of prevalent defects and disorders. Along with one order enhancement in symmetry allowed Raman modes, new peaks related to disorder and surface defects of SnO 2 NPs were found with significant intensity. Temperature-dependent Raman studies were also carried out for these NPs and correlated with the TERS spectra. For quasi-quantum dot sized 4-nm NPs, the TERS study was found to be the best technique to probe the finite size-related Raman forbidden modes.