EMERGING TRENDS IN NANO-OPTICS AND MODERN SPECTROSCOPY Dr. P. M. Anbarasan, Department Of Physics, Periyar University, Salem – 636 011, Tamilnadu, India The increasing trend towards nanoscience and nanotechnology makes it necessary to address the key issues of optics on the nanometer scale. Since the diffraction limit does not allow us to focus light to dimensions smaller than roughly half a wavelength, traditionally it was not possible to interact selectively with nanoscale features. In recent years several new approaches have been put forth to 'shrink' the diffraction limit (confocal microscopy) or to even overcome it (near-field microscopy). For example, with our tip-enhancement technique we are able to do Raman spectroscopy and multiphoton fluorescence imaging with a spatial resolution of less than 20 nm. To date, this is the highest optical resolution of a spectroscopic measurement. TEAM, an instrument to provide unprecedented opportunities to observe atomic scale order, electronic structure and dynamics of individual nanostructures. An Axicon, which is a combined symmetrically Cubic lens phase plate with a perfect lens, is introduced to achieve nanoscale resolution and to delocalize the uniform axial intensity. The results show that this kind of axicon can generate a focal segment with a uniform axial intensity, as expected. By fixing the α and f values and by changing the inner and outer radii of the phase plate, it is possible to delocalize the constant on axial intensity segments of the generated Bessel beam in to a desired ranges. It is also observed that the spot size is in nanoscale and remains constant to certain range in the localized constant on axial segments. Emerging trends in modern spectroscopy by nanoscale resolution is discussed using growth and some characteristics studies on nanocrystalline silicon thin films for solar cells. A series of nano (or synonymously, micro) crystalline silicon films were studied with different microstructural tools such as to elucidate the film microstructure at different stages of growth. Thin Si films, with series of multilayered, were deposited by radio frequency glow discharge using Plasma Enhanced Chemical Vapour Deposition (PECVD) in silane gas (SiH4) highly diluted by hydrogen. Different nanostructured films were prepared by systematically varying gas flow ratios (R =1/1, 1/5, 1/10, 1/15, 1/20)) for films having different thicknesses. By changing the structure of the material, going from pure amorphous to monocrystalline, it is possible to obtain the variation in optical gap using the same material. In these structures layers with different individual optical gaps is stacked together, in order to cover as much of the solar spectrum as possible. The nanostructures of the silicon thin films were studied using OES, FTIR, RS, PL, XRD, SEM, AFM, TEM and HRTEM. Results were correlated for conglomerate surface grain surface. Some numerical modelings were used for designing the overall stack geometry and for interpretation of characterization.
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