F. Singh

On the properties of indium doped ZnO thin films

Thin films of undoped and In-doped zinc oxide, prepared using chemical spray pyrolysis, were investigated using x-ray diffraction, optical transmission and absorption spectra, SEM, resistivity measurements, x-ray photoelectron spectroscopy and photoluminescence studies. A doping level of 1 at% indium was found to give lowest resistive films and enhanced optical transmission. But increasing the doping percentage resulted in lower optical transmission. XPS investigations revealed the presence of elemental chlorine in the In-doped film. Undoped ZnO thin films gave a strong blue-green emission. Doping with indium apparently resulted in a competitive phenomenon that overshadows the blue-green emission and gave rise to three emissions at 408, 590 and 688 nm.

Effects of 160 MeV Ni12+ ion irradiation on HCl doped polyaniline electrode

Conducting polymers are suitable as electrode materials for high performance supercapacitors because of their high specific capacitance and high dc conductivity in the charged state. Ion beam (energy >1 MeV) irradiation of materials is a novel technique to modify their properties. Polyaniline conducting polymer thin films doped with HCl are synthesized electrochemically on indium tin oxide coated glass substrates and are irradiated with 160 MeV Ni12+ ions at different fluences, namely, 5 × 1010, 5 × 1011 and 3 × 1012 ions cm−2. The dc conductivity measurements of the irradiated films showed up to 70% increase in conductivity, which may be due to the increase of carrier concentration in the polymer film as observed in UV-Vis spectroscopy and other effects like the cross linking of polymer chains, bond breaking and creation of defects sites. An x-ray diffractogram study shows that the degree of crystallinity of polyaniline increases upon swift heavy ion (SHI) irradiation with the increase in ion fluence. The capacitance of the irradiated films is lowered but that of the supercapacitors with irradiated films showed enhanced electrochemical stability compared with the devices with unirradiated films while characterized for a cycle life up to 10 000 cycles. This effect could possibly be ascribed to the stabilization of volatile surface groups upon SHI irradiation.

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...

Modifications of ZnO thin films under dense electronic excitation

Spray pyrolyzed ZnO films prepared using solution containing ethanol and water (volume ratio 1:1), exhibited optical transmission of 85% in the visible range and electrical resistivity of 78Ωcm. These samples were irradiated using 120MeV Au ion beam and then characterized using optical absorption and transmission, x-ray diffraction (XRD), electrical resistivity measurements, x-ray photoelectron spectroscopy (XPS), and photoluminescence studies. It appears that irradiation does not affect absorption edge while optical transmittance was slightly reduced. But intensities of peaks of XRD and photoluminescence were found to decrease continuously with increasing ion fluence. Electrical resistivity of the films decreased considerably (from 78to0.71Ωcm) with increase in ion fluence. Atomic concentration from XPS analysis showed that Zn∕O ratio is getting increased due to ion beam irradiation. Variations in carrier concentration were also measured using Hall measurements.

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 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.

Swift heavy ion induced structural and optical modifications in LiF thin film

Thermally deposited 200 nm polycrystalline films of lithium fluoride (LiF) grown on glass substrates were irradiated with 150 MeV Ag ions at various fluences between 1 × 1011 and 2 × 1013 ions cm−2. The irradiation induced structural and optical modifications were studied using glancing angle x-ray diffraction (GAXRD), optical absorption and photoluminescence (PL) spectroscopy. The GAXRD results show that the films are polycrystalline and the average grain size (estimated from the widths of the GAXRD peak using the Scherrer formula) decreases systematically from 46.3 nm for the pristine sample to 18.3 nm for the sample irradiated at a fluence of 3 × 1012 ions cm−2. Thereafter, it remains constant. This reduction is attributed to strain induced fragmentation of grains. The optical absorption studies show dominant absorption bands of F3 (385 nm) and F2 (445 nm) colour centres. It is observed that the concentration of the colour centres increases with ion fluence and gets saturated at higher fluences. This can be correlated with GAXRD results in the sense that as the density of grain boundaries increases the concentration of colour centres also increases. The variation with fluence in PL intensities of the F2 and colour centres is studied. The intensity of both bands (F2 and ) increases up to a fluence of 1 × 1012 ions cm−2, followed by an exponential decrease, which is due to the increase in the non-radiative transition rate in the presence of defect-rich material.

Electronic excitation induced tuning of surface plasmon resonance of Ag nanoparticles in fullerene C70 matrix

We report the electronic excitation induced controlled tuning of the surface plasmon resonance (SPR) wavelength of Ag nanoparticles (NPs) in fullerene C70 matrix. The transformation of fullerene C70 into amorphous carbon (a:C) under ion irradiation is used to tune the SPR wavelength of C70–Ag nanocomposite thin films. A 100 nm blue shift was recorded for irradiation at a fluence of 3 × 1013 ions cm−2 by 120 MeV Ag ions. A growth of Ag NPs from 7.0 ± 0.8 to 11.0 ± 0.4 nm with increasing fluence was observed by transmission electron microscopy and it is explained in the framework of thermal spike model. The transformation of fullerene C70 into amorphous carbon with ion irradiation was confirmed by Raman spectroscopy. This work demonstrates the possibility to locally excite the SPR at a desired wavelength and therefore, acquiring multiple SPR bands at a single substrate which could be useful in developing more efficient optical sensors.

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.