68 research outputs found
Quantitative Analysis of Photo-Thermal Stability of CdSe/CdS Core-Shell Nanocrystals
We report here investigations on the instability in luminescence of bare
(TOPO-stabilized) and CdS- capped CdSe particles under infrared radiation.
During photo-thermal annealing the formation of oxide layers on the surfaces of
the particles create defect states. Consequently there is a reduction in
particle size. These two effects control the light output from the samples. We
make a quantitative comparison of the stability of bare CdSe and core-shell
type CdSe-CdS particles under photo-annealing. Using diffusion theory, we show
that the volume of the oxide layer, adhered to the crystallites, play a
dominant role in controlling the luminosity of the particles.Comment: 10 pages, 4 figure
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.Comment: 9 pages, 4 figure
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.Comment: 15 pages, 6 figure
Raman and photoluminescence studies on thermally annealed porous silicon
We report Raman and Photoluminescence (PL) studies of porous silicon (PS) as a function of isochronal thermal annealing from room temperature to 900°C. The PL peak position and intensity show nonmonotonic variation with increasing temperature. The PL intensity first increases upto 100°C, then decreases till 550°C and recovers its intensity at 700 °C before it completely disappears at 800 °C. The red shifted asymmetric Raman line shape can be fitted by phonon confinement model along with the disordered silicon component. Our results clearly indicate that the origin of visible PL can be better explained by a new hybrid model which incorporates both nanostructures for quantum confinement and silicon complexes (such as SiHx and siloxene) and defects at Si/SiO2 interfaces as luminescent centres
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.Comment: 32 pages, 13 figure
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