882 research outputs found
Quantitative Analysis of Hydrogenated DLC Films by Visible Raman Spectroscopy
The correlations between properties of hydrogenated diamond like carbon films
and their Raman spectra have been investigated. The films are prepared by
plasma deposition technique, keeping different hydrogen to methane ratio during
the growth process. The hydrogen concentration, sp content, hardness and
optical Tauc gap of the materials have been estimated from a detail analysis of
their Raman spectra. We have also measured the same parameters of the films by
using other commonly used techniques, like sp content in films by x-ray
photoelectron spectroscopy, their Tauc gap by ellipsometric measurements and
hardness by micro-hardness testing. The reasons for the mismatch between the
characteristics of the films, as obtained by Raman measurements and by the
above mentioned techniques, have been discussed. We emphasize on the importance
of the visible Raman spectroscopy in reliably predicting the above key
properties of DLC films.Comment: 19 pages, 8 figure
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.Comment: 19 pages 8 figure
A Hybrid model for the origin of photoluminescence from Ge nanocrystals in SiO matrix
In spite of several articles, the origin of visible luminescence from
germanium nanocrystals in SiO matrix is controversial even today. Some
authors attribute the luminescence to quantum confinement of charge carriers in
these nanocrystals. On the other hand, surface or defect states formed during
the growth process, have also been proposed as the source of luminescence in
this system. We have addressed this long standing query by simultaneous
photoluminescence and Raman measurements on germanium nanocrystals embedded in
SiO matrix, grown by two different techniques: (i) low energy
ion-implantation and (ii) atom beam sputtering. Along with our own experimental
observations, we have summarized relevant information available in the
literature and proposed a \emph{Hybrid Model} to explain the visible
photoluminescence from nanocrystalline germanium in SiO matrix.Comment: 23 pages, 8 figure
Sliding wear behavior of submicron-grained alumina in biological environment
Sliding wear behavior of sintered alumina with grain sizes between 0.45 and 4 mu m was studied in bovine serum environment with unidirectional pin-on-disc wear testing machine. Submicron grained alumina of average grain size of G = 0.45 pm exhibits lowest wear factor among the others. It was found that grain pull out or localized grain dislodgement caused by coalescence of grain boundary microcracks is the basic wear mechanism of submicron grained alumina though the extent of cracking and pull-out was substantially less than that with higher grained material. However, in few cases, some areas where substantial volume of material was removed following pull-out of cluster of grains have also been observe
Attenuation of electromagnetic radiation in Nuclear Track Detectors
A systematic study of the attenuation of electromagnetic radiation in Nuclear
Track Detectors (NTDs) is carried out. The attenuation of gamma-ray, X-ray, UV,
visible, and infrared radiation in NTDs are investigated using NaI(Tl)
detector, Gas Electron Multiplier (GEM) detector, UV-Vis spectrophotometer, and
FTIR spectrophotometer respectively. The values of some important parameters
(e.g., optical depth, attenuation coefficient, etc.) of three commercially
available NTDs (PET, Makrofol r and CR-39 r ), at the relevant region of the
electromagnetic spectrum, is determined. The details of the experimental
techniques and the results are also presented in this paper.Comment: 10 page
A central cavity within the holo-translocon suggests a mechanism for membrane protein insertion.
The conserved SecYEG protein-conducting channel and the accessory proteins SecDF-YajC and YidC constitute the bacterial holo-translocon (HTL), capable of protein-secretion and membrane-protein insertion. By employing an integrative approach combining small-angle neutron scattering (SANS), low-resolution electron microscopy and biophysical analyses we determined the arrangement of the proteins and lipids within the super-complex. The results guided the placement of X-ray structures of individual HTL components and allowed the proposal of a model of the functional translocon. Their arrangement around a central lipid-containing pool conveys an unexpected, but compelling mechanism for membrane-protein insertion. The periplasmic domains of YidC and SecD are poised at the protein-channel exit-site of SecY, presumably to aid the emergence of translocating polypeptides. The SecY lateral gate for membrane-insertion is adjacent to the membrane 'insertase' YidC. Absolute-scale SANS employing a novel contrast-match-point analysis revealed a dynamic complex adopting open and compact configurations around an adaptable central lipid-filled chamber, wherein polytopic membrane-proteins could fold, sheltered from aggregation and proteolysis
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