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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