Intense ultraviolet-blue photoluminescence from SiO2 embedded ge nanocrystals prepared by different techniques.

We have made systematic studies on the ultraviolet-blue photoluminescence (PL) from Ge nanocrystals (NCs) grown embedded in SiO2 matrix. Embedded Ge NCs are grown by two different methods, namely, radio-frequency magnetron sputtering (SPT) and ion implantation (IMP). For comparison, Ar implanted SiO2 layer was processed similarly and studied to isolate the contribution of Ge atoms in the observed PL. X-ray diffraction, optical Raman and low frequency Raman scattering studies confirm the presence of Ge NCs in samples prepared by SPT and IMP methods, and Si nanoclusters in Ar implanted sample. Room temperature PL studies with 325 nm excitation show very strong UV-blue emission bands in the range 342-420 nm, and PL studies with 246 nm excitation show two strong UV emission bands at approximately 285 nm and approximately 393 nm in implanted samples. Deconvolution of UV-blue bands show that most of the emission peaks are not unique to the presence of Ge in the samples. Time resolved PL studies in the blue wavelength region show a fast decay dynamics (time constant of approximately 1.0 ns), irrespective of the NC size. PL excitation spectroscopy measurements show a large Stoke's shift for the UV emission bands. Our results indicate that contrary to the literature reports, the approximately 400 nm PL emission is band is not unique to the presence of Ge in the SiO2 matrix and it is likely to originate from a defective NC/SiO2 interface, irrespective of the species of NCs. Origin of various UV emission bands is discussed in the light of the experimental findings and literature reports.

Hydrothermal synthesis of porous triphasic hydroxyapatite/(alpha and beta) tricalcium phosphate.

A novel, porous triphasic calcium phosphate composed of nonresorbable hydroxyapatite (HAp) and resorbable tricalcium phosphate (alpha- and beta-TCP) has been synthesized hydrothermally at a relatively low temperature. The calcium phosphate precursor for hydrothermal treatment was prepared by gel method in the presence of ascorbic acid. XRD, FT-IR, Raman analyses confirmed the presence of HAp/TCP. The surface area and average pore size of the samples were found to be 28 m2/g and 20 nm, respectively. The samples were found to be bioactive in simulated body fluid (SBF).

Preparation of thermally stable nanocrystalline hydroxyapatite by hydrothermal method.

Thermally stable hydroxyapatite (HAp) was synthesized by hydrothermal method in the presence of malic acid. X-ray diffraction (XRD), Fourier transform infra-red spectroscopy (FT-IR), Raman spectroscopy, scanning electron microscopy (SEM), differential thermal analysis (DTA), thermogravimetric analysis (TGA) was done on the synthesized powders. These analyses confirmed the sample to be free from impurities and other phases of calcium phosphates, and were of rhombus morphology along with nanosized particles. IR and Raman analyses indicated the adsorption of malic acid on HAp. Thermal stability of the synthesized HAp was confirmed by DTA and TGA. The synthesized powders were thermally stable upto 1,400 degrees C and showed no phase change. The proposed method might be useful for producing thermally stable HAp which is a necessity for high temperature coating applications.

Growth and characterization of manganese doped gallium nitride nanowires.

Manganese doped GaN nanowires have been grown by chemical vapour transport method on sapphire (0001) substrates in the temperature range of 800-1050 degrees C. The surface features of nanowires have been investigated using Scanning Electron Microscopy (SEM), Energy Dispersive X-ray analysis (EDAX), Raman scattering studies and Electron Paramagnetic Resonance (EPR). SEM images showed that the morphology of the one dimensional materials included straight nanorods and nanowires around 70-80 nm. Raman spectrum showed the GaMnN vibrational modes at 380, 432 and 445 cm(-1). EPR measurements were performed on Mn doped GaN nanowires in order to evaluate the magnetic behaviour.

Synthesis and characterization of charged polystyrene-acrylic acid latex particles.

Novel, monodisperse charged colloidal particles of polystyrene cross linked with divinylbenzene and surface-grafted with acrylic acid were synthesized by emulsion polymerization and were characterized by estimating the dissociable surface charge by conductivity titration, the particle effective charge by conductivity verses particle concentration, and the particle size by dynamic light scattering and atomic force microscopy. The structural ordering and dynamics were investigated as a function of the volume fraction of the particles using static and dynamic light scattering, respectively. Furthermore, from the electrophoresis measurements, these particles are found to have a high salt tolerance due to increases in charge as a function of salt concentration.

Raman and AFM studies of swift heavy ion irradiated InGaAs/GaAs heterostructures.

The effect of swift heavy ion (SHI) irradiation on InGaAs/GaAs heterostructures is studied using Raman spectroscopy and atomic force microscopy (AFM). The structures consist of molecular beam epitaxy (MBE) grown InGaAs layers on GaAs(001), having layer thicknesses of 12, 36, 60 and 96 nm. After irradiation, the GaAs type longitudinal optical (LO) mode blue shifted to higher frequency in thin samples and red shifted towards lower frequency in thick samples. These results are discussed invoking the penetration depth of the probe radiation (λ = 514.5 nm) in InGaAs. Deconvoluting the Raman spectra of thin samples indicates a compressive strain developed in the substrate, close to the interface upon irradiation. This modification and diffusion of indium across the interface results in an increase of strain and reduction of the defect densities in the InGaAs layer. The variations in FWHM of the Raman modes are discussed in detail. The surface morphology of these heterostructures has been studied by AFM before and after SHI irradiation. These studies, combined with Raman results, help to identify different relaxation regimes.

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.