P.K. Kulriya

A comparative study of the effect of O+7ion beam on polypyrrole and CR-39 (DOP) polymers

Polypyrrole thin films doped with para-toluene sulphonic acid were prepared by the electrochemical process. High-energy ion beam irradiation of the polymers is an effective technique to enhance the electrical conductivity, structural property and mechanical properties. So polypyrrole and allyl diglycol carbonate (CR-39 (DOP)) films were irradiated by oxygen ions (energy 100MeV, charge state O +7 ) with fluence varying from 1 × 10 10 to 1 × 10 13 ionscm −2 . The effects of swift heavy ions (SHI) on the structural, optical and surface properties of polypyrrole (Ppy) and CR-39 (DOP) polymers were studied in this work using x-ray diffraction (XRD), UV‐visible spectroscopy and scanning electron microscopy (SEM). XRD patterns of the pristine and irradiated polymer show that the crystallinity improved after the irradiation with SHI. At the low fluence, crystallinity was found to increase but at high fluence, it decreases which could be attributed to cross-linking and degradation mechanism. The UV‐visible spectra show a shift in the absorbance edge towards higher wavelength, which can be correlated with the transition involved in the polymer and variation in the band gap using Tauc’s expression. The band gap of polypyrrole was found to decrease from 3.4 to 3.0eV after irradiation. CR-39 (DOP), however, showed a very large change in the band gap from 4.8 to 3.4eV. The SEM study shows a systematic change in the surface morphology of the polymers with increasing ion fluence. (Some figures in this article are in colour only in the electronic version)

Defect-free ZnO nanorods for low temperature hydrogen sensor applications

Uniformly distributed and defect-free vertically aligned ZnO nanorods (NRs) with high aspect ratio are deposited on Si by sputtering technique. X-ray diffraction along with transmission electron microscopy studies confirmed the single crystalline wurtzite structure of ZnO. Absence of wide band emission in photoluminescence spectra showed defect-free growth of ZnO NRs which was further conformed by diamagnetic behavior of the NRs. H2 sensing mechanism based on the change in physical dimension of channel is proposed to explain the fast response (∼21.6 s) and recovery times (∼27 s) of ZnO NRs/Si/ZnO NRs sensors. Proposed H2 sensor operates at low temperature (∼70 °C) unlike the existing high temperature (>150 °C) sensors.

Temperature dependent electrical transport studies of self-aligned ZnO nanorods/Si heterostructures deposited by sputtering

Self-aligned ZnO nanorods (NRs) were grown on n-Si(100) substrate by RF sputtering techniques. The NRs are uniformly grown on 2-inch wafer along [0001] direction. Single-crystalline wurtzite structure of ZnO NRs was confirmed by X-ray diffraction. The average diameter, height, and density of NRs are found 48 nm, 750 nm, and 1.26 × 1010 cm−2, respectively. The current-voltages (I-V) characteristics of ZnO NRs/Si heterojunction (HJ) were studied in the temperature range of 120–300 K and it shows a rectifying behavior. Barrier height (ϕB) and ideality factor (η) were estimated from thermionic emission model and found to be highly temperature dependent in nature. Richardson constant (A*) was evaluated using Richardson plot of ln(Io/T2) versus q/kT plot by linear fitting in two temperature range 120–180 K and 210–300 K. Large deviation in Richardson constant from its theoretical value of n-Si indicates the presence of barrier inhomogeneities at HJ. Double Gaussian distribution of barrier height with thermionic...

Investigations on the influence of 100 MeV O7+ ion irradiation on the structural, surface morphology and optical studies of gallium nitride epilayers

Swift heavy ion irradiations were carried out on metal organic chemical vapour deposition- grown GaN epilayers on sapphire (0 0 0 1) substrates at room temperature, with 100 MeV O7+ ions and fluences varying from 1×1012, 1×1013 and 5×1013 ions cm−2. The pristine and irradiated GaN samples were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), photoluminescence (PL) and UV–visible optical transmittance studies. XRD results indicate the presence of gallium oxide phases after O7+ ion irradiation and the increase in the Ga2O3 peak intensity and full-width half-maximum of irradiated GaN with increasing ion fluences. Surface morphology was observed from AFM analysis, which indicates a decrease in the root-mean square of roughness from 3.9 to 0.5 nm. PL measurements show a red shift as compared to the as-grown GaN. The UV–visible optical transmittance studies show a decrease in band gap after ion irradiation.

Highly selective and reversible NO2 gas sensor using vertically aligned MoS2 flake networks

We demonstrate a highly selective and reversible NO2 resistive gas sensor using vertically aligned MoS2 (VA-MoS2) flake networks. We synthesized horizontally and vertically aligned MoS2 flakes on SiO2/Si substrate using a kinetically controlled rapid growth CVD process. Uniformly interconnected MoS2 flakes and their orientation were confirmed by scanning electron microscopy, x-ray diffraction, Raman spectroscopy and x-ray photoelectron spectroscopy. The VA-MoS2 gas sensor showed two times higher response to NO2 compared to horizontally aligned MoS2 at room temperature. Moreover, the sensors exhibited a dramatically improved complete recovery upon NO2 exposure at its low optimum operating temperatures (100 °C). In addition, the sensing performance of the sensors was investigated with exposure to various gases such as NH3, CO2, H2, CH4 and H2S. It was observed that high response to gas directly correlates with the strong interaction of gas molecules on edge sites of the VA-MoS2. The VA-MoS2 gas sensor exhibited high response with good reversibility and selectivity towards NO2 as a result of the high aspect ratio as well as high adsorption energy on exposed edge sites.

Improvement in the Sensing Response of Nano-Crystalline ZnO-Based Hydrogen Sensor: Effect of Swift Heavy Ion Irradiation

Hydrogen gas sensing response of RF sputtered nano-crystalline ZnO thin film is improved by ~34.73% using swift heavy ion irradiation technique. X-ray diffraction reveals single crystalline wurtzite structure of ZnO thin films. Full width half maximum (FWHM) of (0002) diffraction peak is decreased with increase in ion fluences. However, at very high fluence 1 × 1013 ions/cm2, crystallinity is degraded while FWHM of diffraction peak increases. The ZnO films were grown under highly compressive stress, which was relaxed with incremental ion fluences up to 1 × 1013 ions/cm2. Cathodoluminescence spectroscopy shows intense predominant peak around ~3.23 eV, which indicates good optical quality of the films. As ion fluence increases, a blue shift appears in near band emission peak from 3.23 to 3.33 eV, which indicates that in-plane stress is decreased. Surface morphology shows generation of self-affine nanostructure and grain fragments as ion fluences were increased. Grain fragmentations had enhanced the surface reaction, and as a result, gas sensors relative response has improved. It was observed that the gas sensors sensitivity is strongly dependent on ion fluences and operating temperature. The sensitivity was enhanced from 66.68% to 89.84% with fluence variations from pristine to 1 × 1012 ions/cm2 at 175 °C operating temperature.