Prabhat Verma 교수

This review discusses a relatively new technique for optical nanoimaging at visible wavelength, known as tip-enhanced Raman spectroscopy (TERS). This technique relies on the enhancement and spatial confinement of light in the close vicinity of the apex of a plasmonic nanotip. The plasmonic nanotip can be positioned on the sample and controlled by a suitable scanning probe microscopy, such as atomic force microscopy or scanning tunneling microscopy. By raster scanning the nanotip, one can obtain

Polarization-dependent low-frequency off-resonant Raman scattering has been studied from various commercially available filter glass samples, which contain ${\mathrm{CdS}}_{x}{\mathrm{Se}}_{1\ensuremath{-}x}$ nanoparticles embedded in a glass matrix. In order to distinguish the confined acoustic phonons from the glass background, the spectra have been compared with those obtained from the base material, which does not contain nanoparticles. Polarized and depolarized scattering from confined acou

Abstract We demonstrate nano‐scale optical analysis of graphene layers by tip‐enhanced near‐field Raman spectroscopy (TERS). In this technique, the spatial resolution ∼30 nm is realized by the near‐field probe which acts as a nano‐light source. From the intensity change of the Raman band of silicon generated from the near‐field probe, we can conveniently estimate the edge boundaries and the number of stacking layers. TERS measurement across the layer edges reveals the nano‐scale properties of th

A comparative study of anharmonic effects in various structural forms of GaAs, namely crystalline, disordered and ion-implanted, and pulse laser annealed (PLA), using temperature-dependent Raman scattering, is reported for various phonon modes over the temperature range 10--300 K. The disordered and PLA samples are found to have greater anharmonicity than crystalline GaAs. The localized vibrational mode in PLA GaAs shows shorter relaxation time than the LO-phonon mode.

Near-field Raman scattering has been utilized to study the interaction between an apertureless metal coated sharp tip and ${\mathrm{C}}_{60}$ molecules. Through local plasmon polaritons generated at the metallized tip, the tip interacts electromagnetically and chemically with the sample molecules, providing an enhanced scattering and high spatial resolution beyond the diffraction limits of the probing light. An additional enhancement was observed under the gap-mode configuration. The sample mole

Abstract The spatial resolution in optical imaging is restricted by so‐called diffraction limit, which prevents it to be better than about half of the wavelength of the probing light. Tip‐enhanced Raman spectroscopy (TERS), which is based on the SPP‐induced plasmonic enhancement and confinement of light near a metallic nanostructure, can however, overcome this barrier and produce optical images far beyond the diffraction limit. Here in this article, the basic phenomenon involved in TERS is revie

Near-field scanning optical microscopy (NSOM) combined with plasmon nanofocusing is a powerful nano-analytical tool due to its attractive feature of efficient background suppression as well as light energy compression to the nanoscale. In plasmon nanofocusing-based NSOM, the metallic tip plays an important role in inducing plasmon nanofocusing. It is, however, very challenging to control plasmonic properties of tips for plasmon nanofocusing with existing tip fabrication methods, even though the

The use of optical antennas in tip-enhanced Raman spectroscopy (TERS) makes it a powerful optical analysis and imaging technique at the nanoscale. Optical antennas can work as nano-light sources in the visible region. The plasmonic resonance of an antenna depends on its length; thus, by varying the length, one can control the enhancement in TERS. In this study, we demonstrated a fabrication method based on focused ion beam milling to realize optical antennas with desired lengths. We then measure

The lattice vibrational properties of new semiconductor alloys, GaAs1−xBix and InAs1−xBix, are reported. These alloys, which were grown by metalorganic vapor phase epitaxy technique, contain a small amount (1.2%–3.8%) of Bi. A detail Raman scattering study of these new alloys, which exhibit weak temperature dependence of the band gap with increasing amount of Bi, is reported here. Good crystalline quality and spatial homogeneity was confirmed using micro-Raman technique. The alloys show ternary

CdS 0.65 Se 0.35 nanoparticles are grown in a glass matrix by thermally annealing a base glass material, in which Cd, S, and Se were introduced by diffusion. The starting base material contains no crystalline structure. A comparative study of the confinement effects on the annealed samples using photoluminescence, low-frequency Raman, and optical Raman scattering experiments is presented. Growth of nanoparticles is observed with the three independent experimental techniques as the annealing temp

Tip-enhanced Raman spectroscopy (TERS) has emerged as a powerful tool for optical imaging at nanoscale spatial resolution, and for investigating the vibrational properties of molecules adsorbed on a substrate. Plasmonic enhancement of the electromagnetic fields near a metallic nanostructure plays a very important role in TERS, where resonant excitation of plasmons is crucial. When two metallic nanostructures are placed at a gap of nanometric distance, their plasmons can interact with one other a

The influence of probing laser power density on the band-edge and the trap luminescence from CdSx Se1-x nanoparticles embedded in a glass matrix is reported. Both the position and the strength of the band-edge luminescence are found to be very sensitive to the laser power. It is observed for the first time that the band-edge luminescence shifts initially towards low energy and then towards high energy with increasing laser power. The results are analysed in terms of laser-induced local heating a