arXiv subjects

Anushree Roy

Publications and source records attributed to Anushree Roy.

32 records · Page 2Linked to original sources

arXiv2011

Raman sensitivity to crystal structure in InAs nanowires

We report a combined electron transmission and Raman spectroscopy study of InAs nanowires. We demonstrate that the temperature dependent behavior of optical phonon energies can be used to determine the relative wurtzite fraction in the InAs nanowires. Furthermore, we propose that the interfacial strain between zincblende and wurtzite phases along the length of the wires manifests in the temperature-evolution of the phonon linewidths. From these studies, temperature-dependent Raman measurements emerge has a non-invasive method to study polytypism in such nanowires.

cond-mat.mes-hall↗

arXiv2010

Evidence of Conformational Changes in Adsorbed Lysozyme Molecule on Silver Colloids

In this article, we discuss metal-protein interactions in the Ag-lysozyme complex by spectroscopic measurements. The analysis of the variation in relative intensities of SERS bands reveal the orientation and the change in conformation of the protein molecules on the Ag surface with time. The interaction kinetics of metal-protein complexes has been analyzed over a period of three hours via both Raman and absorption measurements. Our analysis indicates that the Ag nanoparticles most likely interact with Trp-123 which is in close proximity to Phe-34 of the lysozyme molecule.

physics.bio-ph↗

arXiv2010

Interaction of (-)-epigallocatechin gallate with silver nanoparticles

Interactions between silver nanoparticles and (-)-epigallocatechin gallate (EGCG) have been investigated. Prior to the addition of EGCG molecules the silver particles are stabilized by borate ions. Studies on the surface plasmon resonance band of silver particles suggest that the EGCG molecules remove the borate ions from the surface of the metal particles due to the chelating property of the ions. The complex formation by EGCG and borate ions has been confirmed by NMR studies and pH titration. A possible scheme of interaction between the two has been proposed.

physics.bio-ph↗

arXiv2008

Steiner trees and spanning trees in six-pin soap films

We have studied the Steiner tree problem using six-pin soap films in detail. We extend the existing method of experimental realisation of Steiner trees in $n$-terminal problem through soap films to observe new non-minimal Steiner trees. We also produced spanning tree configurations for the first time by our method. Experimentally, by varying the pin diameter, we have achieved these new stable soap film configurations. A new algorithm is presented for creating these Steiner trees theoretically. Exact lengths of these Steiner tree configurations are calculated using a geometrical method. An exact two-parameter empirical formula is proposed for estimating the lengths of these soap film configurations in six-pin soap film problem.

cs.CG↗

arXiv2006

pH Dependent surface enhanced Raman study of Phe + Ag Complex and DFT calculations for spectral analysis

Surface enhanced Raman spectra of Phenylalanine (Phe) in Ag colloidal solution have been recorded for Phe solutions of different pH. Spectral line-shape analyses of the enhanced modes, at 1005, 1380 and 1582 cm-1, between pH 4.5 and 10.5, have been carried out. The variation of spectral line-width with pH reveals two possible mechanisms in solution: (i) the fluctuation of pH in microscopic volume in an overall uniform pH solution and/or (ii) the motional narrowing caused by the intermolecular ionic interaction. We suggest that different charge states of the reference molecule are responsible for the observed bond softening with decrease in pH. The observed Raman shift and the Raman activity of the vibrational modes with maximum enhancement have been explained by carrying out DFT calculations.

cond-mat.mtrl-sci↗

arXiv2006

Probing liquid surface waves, liquid properties and liquid films with light diffraction

Surface waves on liquids act as a dynamical phase grating for incident light. In this article, we revisit the classical method of probing such waves (wavelengths of the order of mm) as well as inherent properties of liquids and liquid films on liquids, using optical diffraction. A combination of simulation and experiment is proposed to trace out the surface wave profiles in various situations (\emph{eg.} for one or more vertical, slightly immersed, electrically driven exciters). Subsequently, the surface tension and the spatial damping coefficient (related to viscosity) of a variety of liquids are measured carefully in order to gauge the efficiency of measuring liquid properties using this optical probe. The final set of results deal with liquid films where dispersion relations, surface and interface modes, interfacial tension and related issues are investigated in some detail, both theoretically and experimentally. On the whole, our observations and analyses seem to support the claim that this simple, low--cost apparatus is capable of providing a wealth of information on liquids and liquid surface waves in a non--destructive way.

physics.optics↗

arXiv2006

Optical Properties of Nanocrystalline Y2O3:Eu3+

Optical properties of nanocrystalline red-emitting phosphor, Europium doped Yttria (Y$_{2}$O$_{3}$:Eu$^{3+})$, of average particle size 15 nm are investigated. The intensity of the strongest emission line at 612 nm is found to be highest in the nanocrystalline sample with 4 at. wt. % of Europium. The narrow electronic emission spectrum suggests a crystalline surrounding in this nanomaterial. We have estimated the strength of the crystal field parameter at the dopant site, which plays a crucial role in determining the appearance of the intense emission line. The equilibrium temperature of this system has also been calculated from the intensity ratio of Stokes and anti-Stokes Raman scattering. Though known for the bulk samples, our approach and consequent results on the crystalline nanomaterial of Y$_{2}$O$_{3}$:Eu$^{3+}$ provide a unique report, which, we believe, can be of considerable significance in nanotechnology.the intensity ratio of Stokes and anti-Stokes Raman scattering. Though known for the bulk samples, our approach and consequent results on the crystalline, defect/disorder free nanomaterial of Y2O3:Eu3+ provides a unique report which, we believe, can be of considerable significance in nanotechnology.

cond-mat.mtrl-sci↗

arXiv2005

Comparison of metal-amino acid interaction in Phe-Ag and Tyr-Ag complexes by spectroscopic measurements

In this article, we have compared the metal-amino acid interactions in Tyr-Ag and Phe-Ag complexes through pH dependent SERS measurements. By analyzing the variation in relative intensities of SERS bands with the pH of the amino acid solution, we have obtained the orientation and conformation of the amino acid molecules on the Ag surface. The results obtained from our experimental studies are supported by the the energy minimized strucutres and the observed charge distributions in different terminals of the molecules. This, in a way, shows that SERS measurements not only exhibit the interaction of the amino acid molecules with Ag clusters but also demonstrate their orientation around it. We have addressed a long standing query on whether the amine group is directly attached with Ag surface along with the carboxylate group and $π$-electrons in these systems. In addition, pH dependent optical absorption and transmission electron microscopy measurements have been performed to understand the required conditions for the appearance of the SERS spectra in the light of the aggregation of metal particles and the number of hot sites in the sol. Our results confirm that the formation of hot sites in the sol plays a direct role to form a stable Ag-ligand complex. Furthermore, the interaction kinetics of metal-amino acid complexes have been analyzed via both Raman and absorption measurements.

physics.bio-ph↗

arXiv2004

Electron and Phonon Confinement and New Surface Phonon Modes in CdSe-CdS Core-Shell Nanocrystals

Optical and vibrational properties of bare and CdS shelled CdSe nanocrystalline particles are investigated. To confirm the formation of such nanocrystals in our samples we estimate their average particle sizes and size distributions using TEM measurements. From the line profile analysis of the images the core-shell structure in the particles has been confirmed. The blue shift in optical absorption spectra, analyzed using theoretical estimates based on the effective bond order model, establishes the electron confinement in the nanoparticles. Unique characteristics of the nanocrystals (which are absent in the corresponding bulk material), such as confinement of optical phonons and the appearance of surface phonons, are then discussed. Making use of the dielectric response function model we are able to match the experimental and theoretical values of the frequencies of the surface phonons. We believe that our studies using optical probes provide further evidence on the existence of core-shell structures in CdSe-CdS type materials.

cond-mat.mtrl-sci↗

arXiv2004

A non-destructive analytic tool for nanostructured materials : Raman and photoluminescence spectroscopy

Modern materials science requires efficient processing and characterization techniques for low dimensional systems. Raman spectroscopy is an important non-destructive tool, which provides enormous information on these materials. This understanding is not only interesting in its own right from a physicist's point of view, but can also be of considerable importance in optoelectronics and device applications of these materials in nanotechnology. The commercial Raman spectrometers are quite expensive. In this article, we have presented a relatively less expensive set-up with home-built collection optics attachment. The details of the instrumentation have been described. Studies on four classes of nanostructures - Ge nanoparticles, porous silicon (nanowire), carbon nanotubes and 2D InGaAs quantum layers, demonstrate that this unit can be of use in teaching and research on nanomaterials.

cond-mat.mes-hall↗

arXiv2004

Diffraction of light by interfering liquid surface waves

Interfering liquid surface waves are generated by electrically driven vertical oscillations of two or more equispaced pins immersed in a liquid (water). The corresponding intensity distribution, resulting from diffraction of monochromatic light by the reflection phase grating formed on the liquid surface, is calculated theoretically and found to tally with experiments. The curious features of the diffraction pattern and its relation to the interference of waves on the liquid surface are used to measure the amplitude and wavelength of the resultant surface wave along the line joining the two sources of oscillation. Finally, a sample diffraction pattern obtained by optically probing surface regions where interference produces a lattice--like structure is demonstrated and qualitatively explained.

physics.optics↗

arXiv2000

Improved Precision Measurement of the Casimir Force

We report an improved precision measurement of the Casimir force. The force is measured between a large Al coated sphere and flat plate using an Atomic Force Microscope. The primary experimental improvements include the use of smoother metal coatings, reduced noise, lower systematic errors and independent measurement of surface separations. Also the complete dielectric spectrum of the metal is used in the theory. The average statistical precision remains at the same 1% of the forces measured at the closest separation.

quant-ph↗

arXiv1999

Complete roughness and conductivity corrections for the recent Casimir force measurement

We consider detailed roughness and conductivity corrections to the Casimir force in the recent Casimir force measurement employing an Atomic Force Microscope. The roughness of the test bodies-a metal plate and a sphere- was investigated with the Atomic Force Microscope and the Scanning Electron Microscope respectively. It consists of separate crystals of different heights and a stochastic background. The amplitude of roughness relative to the zero roughness level was determined and the corrections to the Casimir force were calculated up to the fourth order in a small parameter (which is this amplitude divided by the distance between the two test bodies). Also the corrections due to finite conductivity were found up to the fourth order in relative penetration depth of electromagnetic zero point oscillations into the metal. The theoretical result for the configuration of a sphere above a plate taking into account both corrections is in excellent agreement with the measured Casimir force.

quant-ph↗

arXiv1998

Precision Measurement of the Casimir Force from 0.1 to 0.9 microns

We have used an atomic force microscope to make precision measurements of the Casimir force between a metallized sphere of diameter 196 microns and flat plate. The force was measured for plate-sphere separations from 0.1 to 0.9 microns. The experimental results are consistent with present theoretical calculations including the finite conductivity, roughness, and temperature corrections. The root mean square average deviation of 1.6 pN between theory and experiment corresponds to a 1% deviation at the smallest separation.

physics.optics↗