- Student's Corner
a) Surface Enhanced Raman Scattering Studies
When molecules are placed in close proximity to some metal surfaces, they can exhibit greatly enhanced Raman scattering, which is known as surface enhanced Raman scattering (SERS). As anthraquinone/naphthoquinone derivatives have potential sites such as phenyl ring, carbonyl group and its substituents for adsorption on metal surface, the orientation of the molecule can be through the p electron cloud (flat-on) and the sites available for adsorption (stand-on). Raman spectra of a few anthraquinone and naphthoquinone derivatives adsorbed on silver nanoparticles exhibited several interesting signatures such as activity of a few modes, shifting and broadening of bands and enhancement in intensity. From the orientation of the molecule on the surface, the possible site of adsorption and the role of inter and intra molecular hydrogen bonding were elucidated. b) Study on solute solvent interaction
A Raman spectroscopic investigation of the carbonyl stretching vibrations of 3-phenoxybenzaldehye (3Phbz) and 4-ethoxybenzaldeheyde (4Etob) in binary mixtures with different polar and nonpolar solvents was made as it had importance by twofold: firstly, to describe the interaction of the carbonyl groups of two solute molecules in terms of a splitting in the isotropic and anisotropic components and secondly, to analyze their spectroscopic signatures in a binary mixture. The observed change in wavenumber with solvent concentration did not show linearity, indicating the significant role of molecular interactions on the occurrence of breaking of the self-association of the solute.
Photo physical properties of a few anthraquinone derivatives were analysed in terms of solute–solvent and solvent–solvent interactions by monitoring the optical absorption and fluorescence emission in single solvents as well as in the case of binary mixtures. c) Studies on nano particles
As the optical properties of metal nanoparticle are different from those of bulk materials, nonlinear optical absorption in silver nanosol was investigated at selected wavelengths of excitation. It was observed that the nature of nonlinear absorption is sensitively dependent on input fluence as well as excitation wavelengths. Besides, nanoparticles were found to exhibit reverse saturable absorption and saturable absorption (SA) at excitation wavelengths depending on input fluence.
Fluorescence spectroscopy was used to evaluate the interaction between semiconductor oxide nanoparticles and the derivatives of anthraquinone from the fluorescence quenching/enhancement of fluorophores in the vicinity of semiconductor oxide nanoparticles. d) Raman scattering studies of semiconductor hetero structures
The phonon mode behavior of InGaN/GaN single quantum well (SQW) nanocolumns grown on silicon (111) substrate was investigated using micro-Raman scattering technique. The nature and origin of stress in GaN grown on Si substrate was identified. The dimension of the GaN nanocolumn was calculated from the wavenumber shift of the optical phonons using spatial correlation model and found that the experimental results matched with the theoretical model. e) Raman intensity mapping
Raman intensity mapping of InN-GaN core-shell nanowire provided the information about the crystalline quality.
a)Optical image of InN-GaN core-shell nanowires using micro Raman spectrometer ; the square shaped highlighted area(green) was mapped for intensity distribution using 325 nm excitation; (b) Raman intensity distribution of scattered light with dark and red regions indicating void and higher intensity, respectively; (c-d) The Raman spectra of marked void and red regions.