D. Kabiraj

Synthesis of metal-polymer nanocomposite for optical applications

Thin films of Ag‐PET nanocomposite were synthesized by a novel route of atom beam co-sputtering. The nanocomposites were characterized by UV‐visible and IR absorption spectroscopy, Rutherford backscattering spectroscopy and transmission electron microscopy. The absorption spectra exhibit features suitable for applications as (i) absorber extending from the visible region to about 2400 nm in the infrared region and (ii) bandpass filter at 320 nm, useful for HeCd laser. The transmission electron microscopy observations indicate that the metal fraction is in the form of fractals. (Some figures in this article are in colour only in the electronic version)

Synthesis and characterization of ZnO thin film grown by electron beam evaporation

Highly transparent, conducting, highly oriented, and almost single phase ZnO films have been deposited by simple e-beam evaporation method, and the deposition parameters were optimized. The films were prepared by (a) evaporation of ZnO at different substrate temperatures and (b) evaporation of ZnO at room temperature and subsequent annealing of the films in oxygen ambient at different temperatures. The characterizations of the film were performed by optical absorption spectroscopy (UV-visible), Fourier transform infrared spectroscopy, resistivity measurement, transmission electron microscopy (TEM), photoluminescence, and x-ray diffraction measurement. Absorption spectra revealed that the films were highly transparent and the band gap of the pre- and postannealed films was in good agreement with the reported values. The band gap of the films increases on increasing the substrate temperature as well as annealing temperature, whereas the resistivity of the film decreases with substrate temperature and increa...

Controlled growth of gold nanoparticles induced by ion irradiation: An in situ x-ray diffraction study

Thin silica films containing Au nanoparticles were prepared by cosputtering. The kinetics of the growth of nanoparticles under 90MeV Ni ion irradiation was studied by in situ x-ray diffraction. The growth of nanoparticles from 4 (for pristine) to 9nm at a fluence of 1×1014ions∕cm2 was observed, in accordance with the observations made by transmission electron microscopy analyses. The present study shows that the ion irradiation is an effective tool for tailoring the size of nanoparticles. The results are discussed in the framework of thermal spike model.

Synthesis of gold-silicon core-shell nanoparticles with tunable localized surface plasmon resonance

Gold-silicon core-shell nanoparticles embedded in silica matrix, evident by transmission electron microscopy and x-ray photoelectron spectroscopy were synthesized by atom beam cosputtering followed by thermal annealing. Optical absorption studies revealed localized surface plasmon resonance (LSPR), which showed regular redshift from 500to583nm with increase in annealing temperature. The observed redshifts in the LSPR peaks are in close agreement with the theoretical calculations assuming Si nanoshells surrounding Au nanoparticles. The Au–Si core-shell formation is explained by Au–Si liquid nanodroplet formation at temperatures higher than the eutectic temperature, followed by phase separation during subsequent cooling.

Synthesis of confined electrically conducting carbon nanowires by heavy ion irradiation of fullerene thin film

Conducting nanowires parallel to each other, embedded in fullerene matrix are synthesized by high energy heavy ion irradiation of thin fullerene film at low fluence (up to 5×1011ions∕cm2). The conductivity of the conducting zone is about seven orders of magnitude higher than that of the fullerene matrix. The conducting nanowires are evidenced by conducting atomic force microscopy. The typical diameter of the conducting tracks is observed to be about 40–100nm. The creation of conducting wires is explained by transformation of fullerene to conducting form of carbon in the ion track, surrounded by the polymerized zone. The polymerization of fullerene is evidenced by Fourier transform infrared spectroscopy.

Gold-silica nanocomposites for the detection of human ovarian cancer cells : a preliminary study

We report the structural and optical properties of Au nanoparticles embedded in a silica matrix synthesized by atom beam co-sputtering. The presence of surface plasmon resonant absorption indicates the formation of Au nanoparticles. Transmission electron microscopy (TEM) studies show the presence of Au nanoparticles with an average size ranging from ~1.8 to 5.4 nm with narrow size distributions depending on the relative areas of Au and SiO2. We discuss the process of nucleation and growth of Au nanoparticles in the nanocomposite films formed by co-sputtering. The present method of nanoparticle synthesis is compared with other ion beam based techniques such as ion implantation and ion beam mixing. Preliminary experiments for the detection of human ovarian cancer cells using these Au nanoparticles are described.

Formation of self-affine nanostructures on ZnO surfaces by swift heavy ions

The topography evolution using the high energy heavy ion irradiation revealed the fact that ion bombardment produces self-affine nanostructures, creating peculiar surface morphologies and regular structures on the surface of the ZnO thin film at certain fluences. The self-affine nanopatterns produced on the surface of ZnO thin film under swift heavy ion irradiation are different types of nanostructures such as nanodimensional grains aligned like a linear array. Scanning probe microscopy is used for investigating the ZnO surfaces and UV-visible spectroscopy for studying the effect of surface modification on optical properties. The two-dimensional power spectral density of the irradiated ZnO thin films have been evaluated for each image to extract the value of growth factor (β) and roughness exponent (α). The exponent n increases from 2.2 to 4.0 up to a critical value of fluence and beyond which it decreases. These values suggest that ion assisted∕induced diffusion process plays a crucial role in the evolution of self-affine nanostructures on ZnO surface.The topography evolution using the high energy heavy ion irradiation revealed the fact that ion bombardment produces self-affine nanostructures, creating peculiar surface morphologies and regular structures on the surface of the ZnO thin film at certain fluences. The self-affine nanopatterns produced on the surface of ZnO thin film under swift heavy ion irradiation are different types of nanostructures such as nanodimensional grains aligned like a linear array. Scanning probe microscopy is used for investigating the ZnO surfaces and UV-visible spectroscopy for studying the effect of surface modification on optical properties. The two-dimensional power spectral density of the irradiated ZnO thin films have been evaluated for each image to extract the value of growth factor (β) and roughness exponent (α). The exponent n increases from 2.2 to 4.0 up to a critical value of fluence and beyond which it decreases. These values suggest that ion assisted∕induced diffusion process plays a crucial role in the evolut...

Synthesis and characterizations of silver-fullerene C70 nanocomposite

Films of C70 fullerene containing silver nanoparticles were synthesized by thermal codeposition. Optical absorption studies revealed that surface plasmon resonance of Ag nanoparticles occurs at unusually large wavelength, which showed a regular redshift from 521 to 581 nm with increase in metal content from 4.5% to 28%. It is explained by the Maxwell–Garnett theory considering the absorbing nature of fullerene matrix. Rutherford backscattering and transmission electron microscopy were performed to quantify metal content and the particle size, respectively. A better detection of low intensity vibrational modes of C70 in Raman scattering is observed due to surface enhanced Raman scattering.

Thermal and ion induced annealing of nanocrystalline ZnO thin film deposited by atom beam sputtering

ZnO thin films were deposited using atom beam sputtering and their modifications have been shown by two processes: (a) thermal annealing of ZnO thin films in oxygen and (b) athermal annealing by irradiation of these films by swift heavy ions (SHIs) in a high vacuum chamber. The as-deposited films showed the nanocrystalline nature with a preferred orientation along the c-axis of the hexagonal structure as revealed by x-ray diffraction (XRD) and Raman spectra. The influence of the thermal annealing and athermal annealing on the structural and surface modifications of these thin films were investigated. XRD and Raman spectroscopy confirmed the improvement in the crystallinity of ZnO thin film by both thermal annealing and SHI irradiation. The Zn–O bonding was confirmed by Fourier transform infrared spectroscopy and the interpretation of IR spectra corroborated the XRD and Raman results. Surface morphology was investigated by atomic force microscopy. The AFM study of the films implied no significant change in the roughness of the films in both types of annealing conditions. It was concluded that the modification of nanocrystalline ZnO thin film could be possible by both thermal and athermal annealing. Results indicate that transient annealing by SHI irradiation induces the highly textured c-axis oriented ZnO thin film for device applications, comparable to those of high temperature annealing.

Swift heavy ion-induced dissolution of gold nanoparticles in silica matrix

Gold nanoparticles embedded in silica matrix were prepared by co-evaporation. After deposition, the samples were annealed at different temperatures in inert environment for 30 min. No signature of nanoparticle formation was found in case of as-deposited samples, while the annealed samples showed a clear signature of a surface plasmon resonance absorption peak around 520 nm, which indicated the formation of Au nanoparticles. The samples annealed at 900 °C were irradiated with 100 MeV Ag ions at fluences 2.5×1012 and 1×1013 ions/cm2. UV-visible absorption measurements of pristine and irradiated films showed a clear signature of dissolution of Au nanoparticles with ion beam fluence. X-ray diffraction studies of pristine and irradiated samples also supported the dissolution of Au nanoparticles with ion beam fluence. Rutherford backscattering spectrometry was used for quantification of gold.