R. Kesavamoorthy

Optical absorption and photoluminescence spectroscopy of the growth of silver nanoparticles

Results obtained from the optical absorption and photoluminescence (PL) spectroscopy experiments have shown the formation of excitons in the silver-exchanged glass samples. These findings are reported here for the first time. Further, we investigate the dramatic changes in the photoemission properties of the silver-exchanged glass samples as a function of postannealing temperature. Observed changes are thought to be due to the structural rearrangements of silver and oxygen bonding during the heat treatments of the glass matrix. In fact, photoelectron spectroscopy does reveal these chemical transformations of silver-exchanged soda glass samples caused by the thermal effects of annealing in a high vacuum atmosphere. An important correlation between temperature-induced changes of the PL intensity and thermal growth of the silver nanoparticles has been established in this Letter through precise spectroscopic studies.

Raman spectroscopic and photoluminescence investigations on laser surface modified α-Al2O3 coatings

Abstract Laser surface modification of plasma sprayed alumina coatings were carried out for obtaining desired structural and microstructural transformations. Appearance of Raman modes was used to detect the transformation of Al2O3 from γ to α phase. Photoluminescence due to the natural occurrence of Cr3+ ions was used to probe the densification and enhancement of the surface quality of the coatings brought about by laser treatment.

Influence of deposition temperature on the growth of vacuum evaporated V2O5 thin films

V2O5 films were deposited on silicon (111) substrates by vacuum evaporation technique at various deposition temperatures of 300, 473, 573, 623 and 673 K. X-ray characterization revealed that the films deposited at Ts≤473 K are amorphous and the film deposited at Ts≥573 K is polycrystalline. It is interesting to note that the film deposited at Ts=573 K is strongly oriented with (001) planes parallel to the substrate and the degree of preferred orientation towards (001) planes found to decrease with further increase in the deposition temperature. The influence of deposition temperature on the growth of the V2O5 films has been studied by Raman scattering spectroscopy. The films deposited on the silicon substrates maintained at 573 K are found to have better structural quality.

Microscopic observations of ordering in dilute charged colloids

Ordering in dilute charged colloids is investigated using an optical reflection microscope, a video camera and an image processor. About six layers of colloidal crystal have been observed from the wall of the container. Grain boundaries, dislocations, voids and vacancies are observed along the depth of the colloidal crystal. The stable crystal structure and orientation of the crystal are identified and understood. The effect of the container wall on the ordering is analysed. The individual and collective motions of particles in the crystal are reported. The effect of aggregates on the crystalline order and the vibration of aggregates in the crystal are studied. The controversy over the inter-particle potential is addressed and the potential appears to have an attractive term like that in a Sogami potential.

Raman scattering and optical absorption studies of Ar+ implanted CdS thin films

Abstract The effect of argon ion implantation on chemical bath deposited Cadmium sulphide (CdS) thin films is investigated by X-ray diffraction, Raman scattering and optical absorption techniques. The X-ray diffraction pattern of the As-deposited CdS thin films shows the presence of both sphalerite (cubic) and wurtzite (hexagonal) phases. Phase transition from the As-deposited mixed phase to the more stable hexagonal phase along with grain growth is observed on post implantation annealing. Optical absorption studies of the implanted films reveal a reduction in the band gap on implantation and its recovery to As-deposited values on post implantation annealing. A decrease in the intensity of the Raman peak of CdS A 1 (LO) mode is seen on implantation and on post implantation annealing, the intensity is found to increase. A drastic reduction in the full width at half maximum (FWHM) value of the films subjected to post implantation annealing compared to that of As-deposited or implanted films suggests the removal of defects and strain during annealing. The peak position of the Raman mode of CdS remains more or less the same.

Raman Scattering Studies of Ar+ Implanted CdS Films Prepared by Vacuum Evaporation

CdS thin films were prepared by vacuum evaporation onto glass substrates at room temperature. X-ray diffraction and TEM studies revealed that the as-deposited CdS thin films have a wurtzite (hexagonal) structure, and have been grown with preferential (0002) orientation. The Raman peak of the as-deposited CdS thin film appeared at 303.12 cm -1 with a full width at half maximum (FWHM) of 8.3 cm -1 . These films were implanted with a mass analyzed beam of 100 keV Ar + ions to various doses in the range of 10 14 to 10 16 ions/cm 2 . Contrary to the expected reduction in the Raman intensity, there was a monotonic increase in the intensity of the Raman peak with implantation dose. The Raman peak position of the CdS A 1 (LO) mode did not change much whereas the full width at half maximum (FWHM) was found to increase with implantation dose. These results are explained on the basis of the implantation induced surface roughness and lattice disorder.

The effect of nitrogen ion implantation on the structural, optical and electrical properties of ZnSe thin films

Zinc selenide thin films were deposited onto well-cleaned glass and silicon substrates using the vacuum evaporation technique under a vacuum of 3 × 10−5 Torr. These films were implanted with mass-analysed 75 keV N+ ions at different doses ranging from 1014 to 1016 ions cm−2. The composition, microstructure, surface roughness, optical bandgap and electrical properties of the as-deposited and nitrogen-implanted films were studied by Rutherford backscattering (RBS), grazing incidence x-ray diffraction (GIXRD), atomic force microscopy (AFM), Raman scattering, optical transmittance and I–V measurements. The RBS analysis indicates that the composition of the as-deposited and nitrogen-implanted films is nearly stoichiometric. The thickness of the as-deposited film is calculated as 230 nm. The structure of the as-deposited and nitrogen-implanted thin films is cubic. In the AFM analysis, the surface roughness is found to increase with an increasing dose of nitrogen ions. In the optical studies, the optical bandgap value decreases with increase of the N+ dose. The prepared device exhibits a very good response in the visible region.

Raman studies in nanocrystalline lead (II) fluoride

Nanocrystalline lead fluoride was prepared by an inert gas condensation technique under ultra-high vacuum conditions. Structural studies were carried out with x-ray diffraction analysis. As-prepared and vacuum annealed samples were found to contain both orthorhombic (?) and cubic (?) phases of PbF2. The annealed samples contain dominantly the cubic phase. Grain sizes were found to be in the range from 21 to 43?nm. Raman scattering measurements have been performed on these samples in different frequency regions. Characteristic phonon vibrational modes such as T2g for ?-PbF2 have been observed in addition to some modes corresponding to ?-PbF2. The Raman lines were assigned to ? and ?-PbF2 on comparison with the already reported, both calculated and experimental, values. Some new modes have also been observed at the higher frequency region. The modes at higher frequencies were correlated to vibrations of electronic centres whose density varied with annealing temperature. The presence of electronic centres was investigated by photoluminescence studies. The widths of the Raman spectral lines were found to decrease with the increase in grain size. Low-frequency Raman studies revealed the presence of structural defect clusters. The defect cluster size was found to increase with annealing temperature.

Raman scattering studies of oxygen implanted CdS thin films prepared by vacuum evaporation

CdS thin films prepared by vacuum evaporation method were implanted with oxygen ions at the energy of 80 keV to different doses. Raman scattering studies of the as-deposited and implanted films reveal the shift in the Raman peak position of A1(LO) mode towards higher wave number on implantation. The area under the peak increases with dose initially, and then decreases at higher doses. The shift of the Raman peak to higher wave numbers has been attributed to the replacement of sulphur atoms by the lighter oxygen atoms.

The two-dimensional crystalline-like ordering at the surface of a bulk colloidal suspension

Ordering in dilute charged colloidal suspensions is investigated using an optical reflection microscope, a video camera and an image processor. The surface of the bulk suspension contained in a glass container is imaged and analysed. The fraction of six coordinated particles and the distribution of nearest-neighbour distances are computed from the micrograph and are used to characterize the degree of ordering in different layers. The degree of ordering is found to reduce from the surface layer towards the inner layers. The pair-correlation functions and angular correlation functions are computed from the micrographs. Algebraic decay of the pair correlation function and the distance independent angular correlation function indicates two-dimensional crystalline-like ordering of the particles at the surface of the bulk colloidal suspension. A possible cause for such an ordering is discussed.