K. G. M. Nair

Correlation between microstructure and optical properties of ZnO nanoparticles synthesized by ball milling

Zinc oxide (ZnO) nanoparticles (NPs) in the size range ∼7–35 nm are synthesized by ball-milling technique, and microstructural and optical properties of the NPs are studied using varieties of techniques. Results from ball-milled NPs are compared with those of the commercially available ZnO nanopowder. X-ray diffraction pattern of the milled NPs indicates lattice strain in the NPs. High-resolution transmission electron microscopy analysis reveal severe lattice distortion and reduction in lattice spacing in some of the NPs. Optical absorption spectra of milled NPs show enhanced absorption peaked at 368 nm, which is blueshifted with reference to starting ZnO powder. Room-temperature photoluminescence spectra show five peaks consisting of ultraviolet and visible bands, and relative intensity of these peaks drastically changes with increasing milling time. Raman spectra of milled powders show redshift and broadening of the Raman modes of ZnO, and a new Raman mode evolve in the milled NPs. A correlation between...

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.

Absorption and luminescence of silver nanocomposite soda-lime glass formed by Ag+–Na+ ion-exchange

Metal nanocomposite glasses are formed by a multi step methodology which involves incorporation of the metal ions into the glass by ion-exchange process followed by suitable treatments like low mass ion irradiation or thermal annealing resulting in the aggregation of the metal ions to form nano dimension metal clusters. These embedded metal nanoclusters are well investigated by the optical absorption spectroscopy which gives information regarding the size and shape of the metal clusters embedded in the dielectric matrix. The Ag{sup +} ion-exchanged and annealed soda-lime glasses exhibit photoluminescence around 445 nm at two excitation wavelengths. He{sup +} ion irradiation of the ion-exchanged soda-lime glass resulted in the formation of Ag metal nano crystallites with a thin metal film on the irradiated surface. The Glancing incidence X-ray diffraction study confirmed the formation of Ag nano crystals inside the dielectric matrix. Photoluminescence vanished in the irradiated samples with the neutralization of Ag{sup +} ions into Ag metal nano crystallites.

Raman scattering studies on silver nanoclusters in a silica matrix formed by ion-beam mixing

The formation and growth of nanoscale silver clusters in silica matrices are studied by means of optical absorption and Raman scattering spectroscopy. The metallic silver layer of the Ag/SiO2 couple was irradiated by argon ions for ion-beam mixing of silver with the silica matrix. Postannealing of the embedded Ag atoms in silica matrices results in the growth of Ag nanoclusters. The quadrupolar surface acoustic vibrational mode of the Ag nanoclusters has been observed in low-frequency Raman scattering experiments. The average size of these Ag nanoclusters is estimated from the quadrupolar mode frequency. Systematic growth of Ag nanoclusters embedded in silica matrices is observed with the increase of postannealing temperature. We have estimated the activation energy for the diffusion of Ag atoms in irradiated a-SiO2 from the coarsening of these embedded Ag atoms. Development of a peak at about 3 eV in the optical absorption spectra for the samples postannealed at higher temperatures corroborates further t...

Trace Element Studies on Tinospora cordifolia (Menispermaceae), Ocimum sanctum (Lamiaceae), Moringa oleifera (Moringaceae), and Phyllanthus niruri (Euphorbiaceae) Using PIXE

Traditionally, Tinospora cordifolia (Willd.) Hook. F. & Thomson (Menispermaceae), Ocimum sanctum L. (Lamiaceae), Moringa oleifera Lam. (Moringaceae), and Phyllanthus niruri L. (Euphorbiaceae) are some of the commonly used medicinal plants in India for curing ailments ranging from common cold, skin diseases, and dental infections to major disorders like diabetes, hypertension, jaundice, rheumatism, etc. To understand and correlate their medicinal use, trace element studies on the aqueous extract of these medicinal plants have been carried out using particle-induced X-ray emission technique. A 2-MeV proton beam was used to identify and characterize major and minor elements namely Cl, K, Ca, Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, Br, and Sr in them. Results have revealed that these elements are present in varying concentrations in the selected plants. Notable results include very high concentrations of Cl, K, and Ca in all the leaf samples, appreciable levels of Mn in all plants, high Zn content in T. cordifolia, and the aqueous extract of Moringa leaves compared to others and relative higher concentrations of Cr in all the plants.

Crystalline to amorphous transition and band structure evolution in ion-damaged silicon studied by spectroscopic ellipsometry

Crystalline to amorphous transition and subsequent microstructural evolution in silicon induced by Ar+-ion implantation over a wide range of ion fluences (6×1013–1×1017 cm−2) have been investigated by spectroscopic ellipsometry. In the evaluation of the optical and microstructural properties of the damaged layer, the contribution of the surface overlayer to the measured dielectric spectra was separated by fitting a multilayer model with an effective medium approximation. The best fit to the dielectric spectra for disordered silicon could be obtained by taking our highest-fluence implanted (fluence=1×1017 ions/cm2) amorphous silicon (a-Si) data as reference data instead of a-Si data available in the handbook. The derivative spectra as a function of fluence show a distinct and sharp transition from the crystalline to amorphous phase. The threshold fluence for this transition is derived from fitting. Evaluation of standard sum rules and optical moments for imaginary part of the pseudodielectric function reve...

Surface disordering and its correlations with properties in argon implanted CR-39 polymer

The influence of Ar+ implantation induced disordering in the surface layers of the CR-39 polymer on its optical properties and surface hardness has been studied. The specimens were implanted at 130 keV to the doses of 5 × 1014, 1 × 1015, 1 × 1016 Ar+ cm−2. The structural behavior of the pre- and postimplanted specimens was investigated using UV-Visible, Raman, and x-ray diffraction techniques. Formation of disordered graphitelike structures in the implanted layers of polycarbonate has been observed using Raman and UV-Visible spectroscopy. A significant increase in the value of disorder content (Urbach energy) from 0.77 eV to 1.48 eV and a continuous decline in optical bandgap (from 3.43 eV to 2.32 eV) with increasing implantation dose have been observed. This decrease in optical bandgap has been found to have linear dependence on the increase in the Urbach energy, which points toward the formation of disordered structures in the implanted layers of CR-39 polymer. Further, Knoop microhardness is found to b...

Electrical characterization and type conversion in N+ irradiated CdS thin films prepared by chemical bath deposition

Abstract Type conversion due to nitrogen ion irradiation in CdS thin films prepared by chemical bath deposition (CBD) is reported. The films were bombarded with various doses of nitrogen ions in the range 1014–1017 ions/cm2, at an energy of 130 keV. The electrical conductivity of the films was found to increase with increase in nitrogen ion concentration. The temperature dependence of conductivity showed an activation energy of 0.06 eV, indicating shallow level formation due to implantation. Hot-probe measurements revealed p-type conductivity in implanted samples and n-type conductivity in unirradiated samples. X-ray diffraction results revealed CdS to be the predominant phase even after nitrogen ion irradiation.

Photoluminescence of embedded copper nanoclusters in soda-lime glass

Abstract Copper clusters embedded in soda-lime glass are formed by ion-exchange method. These ion-exchanged soda-lime glasses showed a broad bluish green emission band due to the monovalent copper ions introduced into the dielectric matrix during ion-exchange. The ion-exchanged glasses were annealed in air for 1 h at different temperatures and their photoluminescence spectra were recorded at room temperature. It is observed that the intensity of emission increased with the increase in heat treatment temperatures with the photoluminescence peak shifting towards the lower wavelength region. Irradiation of ion-exchanged samples with He + ions of energy 100 keV resulted in vanishing of the photoluminescence due to the stabilization of the Cu + ions embedded in the dielectric matrix, into metal copper nanocrystals.

In vitro corrosion evaluation of nitrogen ion implanted titanium in simulated body fluid

Surface modification of commercially pure (CP) titanium was attempted by nitrogen ion implantation to investigate corrosion resistance in simulated body fluid. Nitrogen ion was implanted at 70 keV energy for different doses ranging from 5 × 1015 to 2.5 × 1017 ions/cm2. In Vitro Open Circuit Potential (OCP-time measurements and cyclic polarization studies were carried out to evaluate the corrosion resistance of the implanted specimens with reference to the unimplanted one. Specimens implanted at 4 × 1016 and 7 × 1016 ions/cm2 showed optimum corrosion resistance, and implantation beyond this dose deteriorated the corrosion resistance. Gracing Incidence X-ray diffraction (GIXD) was employed on implanted specimens to understand the phases formed with increasing doses. The results of the present investigation indicated that nitrogen ion implantation can be used as a viable method for improving corrosion resistance of titanium. Nature of the surface and reason for the variation and improvement in corrosion resistance are discussed in detail. In vitro Korrosionsuntersuchung von Stickstoffionen-dotiertem Titan in simulierter Korperflussigkeit Durch Stickstoffionen-Dotierung wurde eine Oberflachenmodifikation von handelsublichem, reinen Titan vorgenommen, um den Korrosionswiderstand in simulierter Korperflussigkeit zu untersuchen. Stickstoffionen wurden bei einer Energie von 70 keV bei unterschiedlichen Dosen von 5 × 1015 bis 2,5 × 1017 Ionen/cm2 eingebracht. In vitro wurde das freie Korrosionspotential in Abhangigkeit von der Zeit bestimmt sowie zyklische Polarisationsmessungen durchgefuhrt, um den Korrosionswiderstand der dotierten Proben im Vergleich zu undotierten Proben zu untersuchen. Proben, die mit 4 × 1016 und 7 × 1016 Ionen/cm2 dotiert wurden, zeigten den besten Korrosionswiderstand, wahrend eine Dotierung oberhalb dieser Dosis den Korrosionswiderstand verschlechterte. Um die bei zunehmender Dosis sich bildenden Phasen zu verstehen, wurden GIXD-Messungen eingesetzt. Die Ergebnisse der vorliegenden Untersuchung zeigen, das die Stickstoffionen-Dotierung als eine realisierbare Methode zur Verbesserung des Korrosionswiderstandes von Titan genutzt werden kann. Die Beschaffenheit der Oberflache und die Grunde fur die Variation und Verbesserung des Korrosionswiderstandes werden ausfuhrlich diskutiert.