Surendra Singh Barala

Bio: Surendra Singh Barala is an academic researcher from Indian Institute of Technology, Jodhpur. The author has contributed to research in topics: Irradiation & X-ray photoelectron spectroscopy. The author has an hindex of 3, co-authored 7 publications receiving 30 citations.

Effect of gamma irradiation on Schottky-contacted vertically aligned ZnO nanorod-based hydrogen sensor.

Abstract: We report the impact of gamma irradiation on the performance of a gold Schottky-contacted ZnO nanorod-based hydrogen sensor. RF-sputtered vertically aligned highly c-axis-oriented ZnO NRs were grown on Si(100) substrate. X-ray diffraction shows no significant change in crystal structure at low gamma doses from 1 to 5 kGy. As gamma irradiation doses increase to 10 kGy, the single crystalline ZnO structure converts to polycrystalline. The photoluminescence spectra also shows suppression of the near-band emission peak and the huge wide-band spectrum indicates the generation of structural defects at high gamma doses. At 1 kGy, the hydrogen sensor response was enhanced from 67% to 77% for 1% hydrogen in pure argon at a 150 °C operating temperature. However, at 10 kGy, the relative response decreases to 33.5%. High gamma irradiation causes displacement damage and defects in ZnO NRs, and as a result, degrades the sensor's performance as a result. Low gamma irradiation doses activate the ZnO NR surface through ionization, which enhances the sensor performance. The relative response of the hydrogen sensor was enhanced by ∼14.9% with respect to pristine ZnO using 1 kGy gamma ray treatment.

Modulation of Pb chemical state of epitaxial lead zirconate titanate thin films under high energy irradiation

Abstract: The chemical states of epitaxial PbZrxTi1-xO3 films were investigated by an X-ray photoelectron spectroscopy as a function of the gamma-ray doses. An anomalous behaviour was observed in Pb4f states, and a core level of Pb4f shifts towards a higher binding energy at 50 kGy and towards a lower binding energy at 200 kGy. The behaviour can be explained by a radiation induced reduction of PbO to metallic Pb. The metal-insulator-metal electrodes were fabricated by lithography, and the current-voltage characteristics were measured. A negative differential resistance (NDR) was observed in the leakage currents at room temperature. A higher current and disappearance of NDR characteristics were found in the 200 kGy irradiated samples, which further confirms the presence of metallic Pb.

High energy photon induced Fermi-level shift of Ba 0.5 Sr 0.5 TiO 3 thin films

Abstract: We have studied surface chemical states of Ba 0.5 Sr 0.5 TiO 3 (BST) thin films as a function of high energy photon doses. BST thin films were deposited on Si substrates by Sputtering technique and post irradiations were carried out with high energy 60 Co gamma radiation. Core-level and Fermi-level spectra were measured by X-ray photoelectron spectroscopy. The gamma-ray irradiated BST films showed a higher binding energy shift of Ba, Sr, and Ti core level with increasing gamma doses due to shift in Fermi level. The Fermi level is shifted towards conduction band by ~ 1.1 eV for 200 kGy gamma irradiated BST with respect to pristine. An increase in full width at half maximum of X-ray diffraction peak and surface roughness were also observed with increasing gamma doses. Higher leakage current and decrease in capacitance with gamma doses are further evidence of higher carrier concentration which is consistent with the shift in Fermi level.

Radiation Induced Response of ${\rm Ba}_{0.5}{\rm Sr}_{0.5}{\rm TiO}_3$ Based Tunable Capacitors Under Gamma Irradiation

Abstract: ${\rm Ba}_{0.5}{\rm Sr}_{0.5}{\rm TiO}_3$ (BST) thin films were deposited on sapphire substrate by RF magnetron sputtering techniques and interdigital capacitor (IDC) structures were fabricated using photolithography. Gamma irradiation induced changes of the BST based tunable capacitor have been investigated under various doses from 0 kGy to 600 kGy. Structural and surface morphological studies have been carried out for un-irradiated and irradiated film and revealed that the grain sizes and crystallinity are strongly depended on gamma irradiation doses. The leakage current is increased with increasing gamma irradiation doses due to creation of charge carriers and large numbers of defect in close proximity, provided path for charge carriers. The capacitance of the IDC devices decreased with increasing gamma dose up to 50 kGy and thereafter capacitance gradually increased with radiation doses and reached higher than the un-irradiated device at 600 kGy for 1 MHz frequency. The observed tunability ( $\sim 25\% $ ) of the un-irradiated device was found nearly constant with gamma irradiation doses. This study shows that gamma ray induced defects play important role to the electrical properties of the devices and the BST based devices are highly resistant to gamma radiation, which reflects possible use in space and nuclear applications.

Effect of Gamma Ray Irradiation on Epitaxial Pb(Zr,Ti)O 3 /SrRuO 3 Tunable Varactor Devices

Abstract: Epitaxial morphotropic PbZr0.52Ti0.48O3 (PZT) thin films were employed to enhance the dielectric tunability of microwave filter devices without compromising the device impedance matching and low bias voltage (<10 V) requirements. Epitaxial heterostructure of ferroelectric PZT(001)/SrRuO3 (SRO) were grown on single crystal SrTiO3 (001) substrates by pulsed laser deposition, and a platinum (Pt) electrode was deposited on top of the PZT film. The tunability of the Pt/PZT/SRO varactor devices are strongly dependent on bias voltage and exhibited good dielectric tunability of 55% at 100 kHz and 10 V. The capacitance (CP) of the heteroepitaxial varactor devices was 105 pF at 10 V applied bias with a corresponding small leakage current of 1 nA. The influence of gamma (γ-ray) irradiation on the intrinsic electrical properties of the epitaxial PZT varactor devices was investigated as a function of the irradiation dose from 0 kGy to 400 kGy, in terms of the capacitance–voltage (C–V) characteristics and loss tangent response. With enhancing γ-ray irradiation doses the ferroelectric capacitance was found to decrease accompanying degradation in the loss tangent values. The results indicate that tunability of the epitaxial PZT ferroelectric thin-film capacitors decreased with increasing gamma irradiation dose and degraded ∼25% at 400 kGy dose than unexposed devices. Possible reasons for the degradation behavior of dielectric properties and tunability due to radiation-induced defects has been discussed.

Enhanced sensing performance of ZnO nanostructures-based gas sensors: A review

Abstract: Metal oxide semiconductors-based gas sensors have been extensively explored due to their high sensing response, cost-effectivity, long-term stability, and simple fabrication. However, their utilization at low operating temperature is still challenging. Thus, reduction in power consumption is highly essential for long-term usage of gas sensors. ZnO nanostructures-based gas sensors are one of the most eligible candidates where a real-time detection of explosive and toxic gases is needed. On this subject, numerous efforts have been made to improve the sensing response at reduced working temperature with the assistance of various methods. In this report, several techniques related to the synthesis of ZnO nanostructures and their efficient performance in sensing are reviewed. The report primarily focuses on different means of improving the sensing properties, such as functionalization of noble metal nanoparticles, doping of metals, inclusion of carbonaceous nanomaterials, using nanocomposites of different MO x , UV activation, and post-treatment method of high-energy irradiation on ZnO nanostructures, with their possible sensing mechanisms. This study will therefore shed light on future proposals of ZnO-based gas sensors showing high sensitivity even at low operating temperature.

The Atomic Nucleus

Abstract: Elementary Nuclear Theory By Prof. Hans A. Bethe and Prof. Philip Morrison. Second edition. Pp. xi + 274. (New York: John Wiley and Sons, Inc.; London: Chapman and Hall, Ltd., 1956.) 50s. net.

Hydrogen gas sensor based on mesoporous In2O3 with fast response/recovery and ppb level detection limit

Abstract: Hydrogen gas sensors were fabricated using mesoporous In2O3 synthesized using hydrothermal reaction and calcination processes. Their best performance for the hydrogen detection was found at a working temperature of 260 °C with a high response of 18.0 toward 500 ppm hydrogen, fast response/recovery times (e.g. 1.7 s/1.5 s for 500 ppm hydrogen), and a low detection limit down to 10 ppb. Using air as the carrier gas, the mesoporous In2O3 sensors exhibited good reversibility and repeatability towards hydrogen gas. They also showed a good selectivity for hydrogen compared to other commonly investigated gases including NH3, CO, ethyl alcohol, ethyl acetate, styrene, CH2Cl2 and formaldehyde. In addition, the sensors showed good long-term stability. The good sensing performance of these hydrogen sensors is attributed to the formation of mesoporous structures, large specific surface areas and numerous chemisorbed oxygen ions on the surfaces of the mesoporous In2O3.

Fast Neutron Radiation Damage Effects on High Resistivity Silicon Junction Detectors. Revision

Abstract: P{sup +}{minus}n{sup {minus}}{minus}n{sup +} silicon radiation detectors made of high resistivity Si material ({rho} {ge} 2 k{Omega}-cm) were irradiated to a neutron fluence of a few times of 10{sup 13} n/cm{sup 2}. Dependence of detector leakage current, reverse bias capacitance, and effective doping concentration of the Si substrate on the neutron fluence have been systematically studied. It has been found that the detector leakage current increases linearly with neutron fluence in the range studies, with a damage constant of {alpha} = 9 {times} 10{sup {minus}17} A/cm ({Delta}I = {alpha}V{Delta}{phi}{sub n}), and the C-V characteristics of detectors irradiated to {phi}{sub n} > 10{sup 12} n/cm{sup 2} become frequency dependent. Models using several defect levels in the band gap are proposed to describe the frequency dependent C-V effects and the electrical field profiles after high neutron fluence irradiation.