Antireflection properties of graphene layers on planar and textured silicon surfaces.

In this study, theoretical and experimental investigations have been carried out to explore the suitability of graphene layers as an antireflection coating. Microwave plasma enhanced chemical vapor deposition and chemically grown graphene layers deposited on polished and textured silicon surfaces show that graphene deposition results in a large decrease in reflectance in the wavelength range of 300-650 nm, especially in the case of polished silicon. A Si3N4/textured silicon reference antireflection coating and graphene deposited polished and textured silicon exhibit similar reflectance values, with the graphene/Si surface showing lower reflectance in the 300-400 nm range. Comparison of experimental results with the finite difference time domain calculations shows that the graphene along with a SiO2 surface layer results in a decrease in reflectance in the 300-650 nm range, with a reflectance value of <5% for the case of graphene deposited textured silicon surfaces. The monolayer and inert character along with the high transmittance of graphene make it an ideal surface layer. The results of the present study show its suitability as an antireflection coating in solar cell and UV detector applications.

Structural, morphological, and optical characterisation of ZnO nanostructures fabricated by electrochemical deposition.

The controlled growth of oriented ZnO nanostructures is desirable for their varied applications. In this study, an electrochemical technique is used for deposition of ZnO. The large area morphology shows sheet-like structures oriented perpendicular to the substrate. X-ray diffraction studies show that the crystallinity and purity of electrodeposited ZnO improved by using a moderate thermal annealing. TEM shows randomly oriented rod-like structures. The Raman spectra further confirm the crystallinity of the films. The photoluminescence spectra show emission peaks in the blue-green visible region. Furthermore, we also investigate the potential of the electrochemically-formed ZnO nanostructures as a suitable template for electrochemical deposition of polypyrrole (Ppy).

Direct determination of the generalized Stokes parameters from the usual Stokes parameters.

We report an experimental method to determine the generalized Stokes parameters for a pair of points in the cross section of an electromagnetic beam, e.g., an expanded laser beam, with the help of a Young's interferometer and a set of polarizers and quarter-wave plates. The method is investigated theoretically using the electromagnetic spectral interference law. The generalized Stokes parameters, owing to their two-point nature, determine the behavior of the single-point polarization properties of the electromagnetic beam at a field point. The present method offers a unique means to determine the two-point parameters (correlation functions) by measuring the usual Stokes parameters (intensities) and the contrast parameters (visibilities) of the beam. The method might be applicable to determine the polarization dependent changes in various optical measurements.