Amit Kumar Chawla

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.

Study of composition dependent structural, optical, and magnetic properties of Cu-doped Zn1−xCdxS nanoparticles

Cu-doped Zn1-xCdxS nanoparticles were synthesized by coprecipitation technique in ice bath at 280 K. The band gap energy of Zn1-xCdxS:Cu nanoparticles can be tuned to a lower energy by increasing t ...

Structural,Wettability and Optical Investigation of Titanium Oxynitride Coatings:Effect of Various Sputtering Parameters

The objective of the present work is to investigate the effect of various sputtering parameters such as nitrogen flow rate,deposition time and sputtering pressure on structural,wettability and optical properties of titanium oxynitride films deposited on glass substrate by reactive magnetron sputtering.The X-ray diffraction graphs of titanium oxynitride films show evolution of various textures of TiO_xN_y and TiN phases with increasing nitrogen flow rate and deposition time,but an increase in sputtering pressure from 4.0 to 8.0 Pa results in decline of various textures observed for TiO_xN_y and TiN phases.The stress and strain calculated by sin~2Ψ method are compressive,which decrease with increasing nitrogen flow rate from 55 to 100 sccm(standard cubic centimeter per minute) and increase with increasing deposition time from 80 to 140 min due to atomic penning effect and increasing thickness of the deposited films.The titanium oxynitride films have contact angle values above 90 deg.,indicating that films are hydrophobic.The maximum contact angle of 109.1 deg.is observed at deposition time of 140 min.This water repellent property can add value to potential protective,wear and corrosion resistant application of titanium oxynitride films.The band gap decreases from 1.98 to 1.83 eV as nitrogen flow rate is increased from 55 to 100 sccm;it decreases from 1.93 to 1.79 eV as deposition time is increased from 80 to 140 min as more nitrogen incorporation results in higher negative potential of valence band N2p orbital.But it increases from 2.26 to 2.34 eV for titanium oxynitride films as sputtering pressure increases from 4.0 to 8.0 Pa.

Enhancement of ferromagnetism in Pd nanoparticle by swift heavy ion irradiation

In this study, the effect of swift heavy ion irradiation on the magnetic properties of the Pd nanoparticles has been investigated. Structural investigations along with superconducting quantum interface device measurements show that ferromagnetic properties of the Pd nanoparticles are due to the deviation of their electronic structure from that of bulk. The electronic structure is further modified due to the creation of defects on ion irradiation, which results in 20 times increase in the saturation magnetization. The present study establishes that the defect induced modification of Pd 4d electronic structure is responsible for the ferromagnetic properties of the Pd nanoparticles.

Structural, optical and electronic properties of nanocrystalline TiN films

Nanocrystalline titanium nitride thin films have been deposited by reactive dc magnetron sputtering in pure N2, Ar–N2 and He–N2 gas mixtures. The influence of the nature of the sputtering gas on the structural, optical and the electronic properties of the nanocrystalline TiN films has been studied. Structural properties were investigated by using x-ray diffraction and an atomic force microscope, optical ones by using a UV–visible spectrophotometer and electronic properties by means of dc four-probe resistivity measurements. The films deposited in an He–N2 gas mixture exhibited a strong (111) texture, while for those deposited in an Ar–N2 mixture under identical conditions, the texture of the films changed from (111) to (200).

Influence of Cobalt Doping on the Physical Properties of Zn0.9Cd0.1S Nanoparticles

Zn0.9Cd0.1S nanoparticles doped with 0.005–0.24 M cobalt have been prepared by co-precipitation technique in ice bath at 280 K. For the cobalt concentration >0.18 M, XRD pattern shows unidentified phases along with Zn0.9Cd0.1S sphalerite phase. For low cobalt concentration (≤0.05 M) particle size, dXRDis ~3.5 nm, while for high cobalt concentration (>0.05 M) particle size decreases abruptly (~2 nm) as detected by XRD. However, TEM analysis shows the similar particle size (~3.5 nm) irrespective of the cobalt concentration. Local strain in the alloyed nanoparticles with cobalt concentration of 0.18 M increases ~46% in comparison to that of 0.05 M. Direct to indirect energy band-gap transition is obtained when cobalt concentration goes beyond 0.05 M. A red shift in energy band gap is also observed for both the cases. Nanoparticles with low cobalt concentrations were found to have paramagnetic nature with no antiferromagnetic coupling. A negative Curie–Weiss temperature of −75 K with antiferromagnetic coupling was obtained for the high cobalt concentration.

VLS-like growth and characterizations of dense ZnO nanorods grown by e-beam process

We present a new approach to produce ZnO nanorods in a reproducible manner at a temperature lower than other physical vapour deposition techniques, such as the vapour‐liquid‐solid mechanism. Arrays of well-aligned ZnO nanorods of uniform diameter have been synthesized on the Si substrate precoated with Au, using a simple electron beam evaporation method without the flow of any carrier gas. Scanning electron microscopy and atomic force microscopy characterizations show that as-grown nanorods are well aligned and uniform in diameter. X-ray diffraction measurements and clear lattice fringes in high-resolution transmission electron microscopy image show the growth of good quality polycrystalline hexagonal ZnO nanorods and a �002 � growth direction. The polarization-dependent studies of near edge x-ray absorption fine structure (NEXAFS) are performed to investigate the electronic structure of the zinc and oxygen ions. The analysis of NEXAFS spectra at different angles of incidence of photon flux indicates the formation of ZnO nanorods having anisotropic behaviour of O and Zn states. The photoluminescence spectrum exhibits strong ultraviolet emission at 385nm and the UV‐visible spectrum also shows a band-gap transition around 390nm indicating the good quality of nanorods. The catalytic growth mechanism of the ZnO nanorods is discussed on the basis of experimental results in this work. (Some figures in this article are in colour only in the electronic version)

Effect of power variation on wettability and optical properties of co-sputtered titanium and zirconium oxynitride films

The present paper deals with deposition of titanium and zirconium oxynitride films prepared from co-sputtering titanium and zirconium targets by reactive RF magnetron sputtering. The effect of power variation on various properties of the deposited films is analysed. The film gets transformed from amorphous to well crystalline oxynitride films with gradual increase of target powers as observed from XRD graphs. The films exhibit hydrophilic and hydrophobic behaviours depending upon the presence of various phases. Surface energy decreases as the film properties change from hydrophilic to hydrophobic due to greater contact angle values. The optical properties were measured by UV–Vis–NIR spectrophotometer, transmission spectra and bandgap values show variation with respect to change in elemental composition as determined from EDS analysis.

Study of nanostructured Al doped ZnO films

Abstract Electroless Al doped ZnO nanostructured thin films were deposited on soda lime glass in the present work. The wet deposited films were dried in air and subsequently annealed in a muffle furnace in air environment. The film deposited samples were characterised by field emission SEM/energy dispersive spectroscopy, X-ray diffraction and ultraviolet-visible spectrophotometer. Microstructure of the Al doped ZnO film is strongly affected by increasing the deposition time and annealing temperature. Surface and cross-sectional morphology of Al doped ZnO film exhibited the dense microstructure as compared to undoped ZnO films. X-ray analysis shows a (101) preferential growth in all the films. The optical properties of the films were analysed in the spectral range of 300–800 nm. The obtained samples are highly transparent with a visual transmittance of >80% at 450 nm.

Influence of Sputtering Gas on Morphological and Optical Properties of Magnesium Films

Abstract The influence of sputtering gas (He & Ar) on the structural properties of Mg thin films has been investigated. The optical property (reflectance) that results from the growth of films at varying substrate temperatures ( T sub ) was also studied. The deposited films were characterized by using X-ray diffraction (XRD), field emission scaning electron microscopy (FE-SEM), atomic force microscopy (AFM) and UV-Vis-NIR spectrophotometer. The smaller crystallite size and lower deposition rate were observed in the presence of Helium atmosphere compared to Argon. Morphology of the films shows 2D hexagonal geometry of grains in the deposition temperature range ( T sub ≈50–150°C) in both the sputtering gases. The surface roughness of the polycrystalline films were found to increase with increase in the deposition temperature of both ambient gases. Optical reflectance of Mg films was measured in near infrared region and larger reflectance was observed from Mg films sputtered in He atmosphere compared to that in argon.