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Influence of fabrication processes on transport properties of superconducting niobium nitride nanowires
No full textFabrication of niobium nitride (NbN) superconducting nanowires based on focused ion beam (FIB) milling and electron beam lithography (EBL) is presented. The NbN films were deposited using reactive magnetron sputtering. Argon-to-nitrogen ratio turned out to be a crucial factor in synthesizing high quality superconducting NbN. Critical temperatures (T-c) of around 15.5 K were measured for films with a thickness of around 10 nm. Zero-field-cooled magnetization was measured to optimize the superconducting properties of ultra thin NbN films. The transport behaviour was studied using conventional resistance vs temperature and current-voltage characteristics down to 2 K. Effect of gallium contamination on superconducting properties has been discussed. Whereas the various processing steps of standard EBL route do not have any significant impact on the superconducting transition temperature as well as on the transition width of nanowires, there is significant degradation of superconducting properties of nanowires prepared using FIB. This has been attributed to gallium ion implantation across the superconducting channel. Although the effect of gallium implantation may have technological limitations in designing fascinating single photon detector architectures, it provides some interesting low-dimensional superconducting properties
Hikami-Larkin-Nagaoka (HLN) Treatment of the Magneto-Conductivity of Bi2Te3 Topological Insulator
No full textWe report the magneto-conductivity analysis at different temperatures under a magnetic field of up to 5 T of a well- characterized Bi2Te3 crystal. Details of crystal growth and various physical properties including high linear magneto-resistance are already reported by some of us. To elaborate upon the transport properties of Bi2Te3 crystal, the magneto-conductivity is fitted to the known Hikami-Larkin-Nagaoka (HLN) equation and it is found that the conduction mechanism is dominated by both surface-driven weak anti-localization (WAL) and the bulk weak localization (WL) states. The value of HLN equation coefficient (alpha) signifying the type of localization (WL, WAL or both WL and WAL) falls within the range of - 0.5 to - 1.5. In our case, the low-field (+/- 0.25 T) fitting of studied crystal exhibited a value of alpha close to - 0.86 for studied temperatures of up to 50 K, indicating both WAL and WL contributions. The phase coherence length (l (phi) ) is found to decrease from 98.266 to 40.314 nm with increasing temperature. Summarily, the short letter reports the fact that bulk Bi2Te3 follows the HLN equation and quantitative analysis of the same facilitates to know the quality of studied crystal in terms of WAL to WL contributions and thus the surface to bulk conduction ratio
Crystal structure refinement, dielectric and magnetic properties of A-site and B-site co-substituted Bi0.90Nd0.10Fe1-xTixO3 (x=0.00, 0.02, 0.05 & 0.07) ceramics
No full textNd and Ti co-doped Bi0.90Nd0.10Fe1-xTixO3 (x = 0.00, 0.02, 0.05 & 0.07) ceramics were prepared via conventional solid state reaction method. The crystal structure was investigated by X-ray diffraction at room temperature. The XRD data was further studied by Rietveld refinement using Full prof suite which revealed the structural transformation from rhombohedral (R3c) into triclinic (P1) phase. Low values of R factors and chi(2) showed good agreement between experimental and refined intensities. The analysis of Raman spectra is consistent with the earlier reported data. Dielectric response of all the prepared samples was analyzed in the frequency range 100 Hz to 7 MHz at different temperatures. All the samples exhibited dispersion in dielectric constant values at lower frequencies and became nearly constant at higher frequencies. With Ti substitution, the dielectric constant became stable at higher frequencies due to suppression of oxygen vacancies. The temperature variation of dielectric constant and tans displayed sharp anomalies in the vicinity of Neel temperature. Impedance spectroscopy disclosed appearance of grain contributions in the prepared samples. Magnetic characterization was performed by using Vibrating sample magnetometer upto a field of 5 kOe at room temperature. The hysteresis loop exhibited inherent antiferromagnetism with a weak ferromagnetism. The maximum remnant magnetization (M-r) is observed for Bi0.90Nd0.10Fe0.95Ti0.05O3 is 3.15 memu/g and the corresponding value of coercive field is 130.65 Oe
Enhancement of Y123 dye-sensitized solar cell performance using plasmonic gold nanorods
No full textThe role of the surface plasmon resonance (SPR) of gold nanorods (Au NRs) on the performance of Y123 dye-sensitized solar cells (DSSC) was investigated. DSSCs were fabricated by incorporating different concentrations (0.6 to 3.0 wt%) of Au NRs into TiO2 photoanodes. With an increase in the concentration of the Au NRs, the light absorption by the Y123 dye loaded photoanodes enhanced linearly, but the charge extraction was susceptible to the concentration of the Au NRs. With optimized concentrations (B1.8 wt%) of the Au NRs, the photocurrent of the DSSC enhanced from 12.45 to 15.74 mA cm(-2), and the power conversion efficiency (PCE) improved from 5.31 to 8.86%. The DSSC performance was also verified using Au nanoparticles (the PCE was enhanced from 5.31 to 7.72%) for comparison with the Au NR DSSC performance, which demonstrated the advantage of the Au NRs' shape effect with longitudinal SPR due to the modified light interaction. To explain the experimental observations of the plasmonic DSSC, the Au NRs' extinction efficiency and spatial distribution of the near-fields in complete and porous TiO2 media were also estimated using the finite-element method
Understanding the Influence of Open-waste Burning on Urban Aerosols using Metal Tracers and Lead Isotopic Composition
No full textOpen-waste burning (OWB) is one of the primary sources of urban aerosols in several developing countries. To better understand the influence of OWB emissions on urban aerosols, total suspended particles (TSP) and size-segregated samples were collected at an open-waste burning site (the Okhla landfill) and two urban sites in New Delhi. The TSP samples were analysed for selected metals (As, Cd, Cr, Cu, Fe, Ni, Pb, Sb, Se, Sn, Sr, V and Zn) using ICP-MS. In general, among the metals, Fe and Zn were mostly dominant, and As, Cd and Se were found in trace concentrations in the majority of the samples. Additionally, Pb concentrations were similar to 5-8 fold higher in urban wintertime samples than other samples. Tin, a tracer for waste-burning aerosols, ranged between 0.055 and 0.675 mu g m(-3)in OWB aerosols. Interestingly, the concentration of Sn was significantly high in the urban wintertime aerosols, specifically, 0.082-0.284 mu g m(-3). Tin also showed a high enrichment factor in the urban wintertime aerosols, suggesting its anthropogenic origin, possibly because of enhanced OWB practices in winter. Waste burning was also found to be one of the primary sources of chromium, which ranged between 0.102 and 0.606 mu g m(-3) in OWB aerosols and between 0.114 and 0.574 mu g m(-3) in urban aerosols. Since Cr(VI) is of interest due to its impact on health, the soluble Cr(VI) concentration was determined and found to be 6.1210.2 ng m(-3) (similar to 1-6% of the total Cr in OWB aerosols compared to 0.33-0.65 ng m(-3) [< 1% of the total Cr]) in urban aerosols. The lead isotopic signatures of OWB aerosols, viz., the (208)pb/(206)pb and (206)pb/Pb-207 ratios, were determined to be 2.1369 +/- 0.0029 and 1.1316 +/- 0.0035, whereas those of the urban aerosols were 2.1369 +/- 0.0026 and 1.1243 +/- 0.0024, respectively. However, the ranges of these values among the different aerosol types were not very distinct and showed discreet overlaps. This Pb isotopic study, along with metal fingerprints, suggests the increased influence of OWB emissions in winter on New Delhi aerosols
Tunneling current in magnetic-ferroelectric-superconducting heterostructures
No full textWe report the tunneling current behavior of magnetic-ferroelectric-superconducting heterostructures for multistates non-volatile random access memory (NVRAM) elements. A heterostructure of La0.67Sr0.33MnO3 (LSMO) (50 nm )/PbZr0.52Ti0. 48O3 (PZT) (5 nm)/Bi-Sr-Ca-Cu-2-O-x (BSCCO) (100 nm)/LaAIO(3) (LAO) architecture was fabricated by pulsed laser deposition technique. The tunneling effects were investigated well above and below the superconducting phase transition temperature (T-s similar to 92 K) of the BSCCO bottom electrode. A divergent current and conductance paths were observed for polarization up and down direction above the coercive field of the ferroelectric tunnel barrier. This behaviour was significant below T-s. where the moderate effect of the external magnetic field was also observed on the tunneling current. The dynamic conductance G(V) data fitted well with Brinkman's model for both polarizations up and polarization down states which suggest the presence of large tunnel electro-resistance
A photoluminescence, thermoluminescence and electron paramagnetic resonance study of EFG grown europium doped lithium fluoride (LiF) crystals
No full textEuropium (Eu) doped LiF crystals have been grown by the Edge-defined film fed growth (EFG) technique. The designing and installation of the furnace used for the growth of the crystals have been discussed in detail. In the present study, Eu (Eu2O3) has been doped in LiF in different concentration (0.02-0.2 wt %). X-ray diffractometry (XRD) and Energy Dispersive X-ray (EDX) spectroscopy confirms the incorporation of Eu in LIF. The influence of Eu on LiF has been investigated through photoluminescence (PL), thermoluminescence (TL) and electron paramagnetic resonance (EPR) in as-grown and annealed crystals. PL emission spectra shows the presence of both Eu3+ and Eu2+ form in the as-grown crystals which is confirmed by EPR results. Whereas, in annealed crystals, Eu is present predominantly as Eu2+ form. This suggests that growing crystals at high temperature (similar to 900 degrees C) in argon gas atmosphere through EFG technique favours the reduction of Eu3+ -> Eu2+. This reduction phenomenon has been explained on the basis of charge compensation model. n. study of the LT: Eu (0.02-0.2 wt %) crystals has been done after irradiation with Co-60 gamma rays. In this study, it has been observed that the TL intensity as well as glow curve structure of LiF: Eu crystals are a strong function of Eu concentration. The maximum TL is observed at Eu concentration of 0.05 wt% at which a well defined glow curve structure with a prominent peak at 185 degrees C and a small peak at 253 degrees C. Beyond this concentration (0.05 wt %), n. intensity decreases due to aggregation of defects in the host. The peak at 185 degrees C in LiF: Eu (0.05 wt %) is certainly due to the presence of Eu2+ associated defects which is also supported by the PL spectra. It has been observed that Eu doping have a key role in creation of more defect levels which lead to the increased number of electron and hole traps. Further, trapping parameters are analysed using glow curve deconvolution method to have an insight study of TL phenomena. Further, TL glow curve structure of as-grown and annealed crystal are distinct which may be attributed to the nature of defect traps formed inside the LiF
Transition from n- to p-type conduction concomitant with enhancement of figure-of-merit in Pb doped bismuth telluride: Material to device development
No full textThe majority of industrial, automobile processes, electrical appliances emit waste heat in the low-temperature range (<573 K), hence efficient thermoelectric materials operating in this range are highly needed. Bismuth telluride (Bi2Te3) based alloys are conventional thermoelectric material for the low-temperature application. The pure Bi2Te3 sample synthesized in this work exhibits n-type conduction. We demonstrate that by small doping of Pb at Bi site a transition in electrical transport form n- to p-type is observed. The figure-of-merit (ZT) of n-type Bi2Te3 is similar to 0.47 and optimized Bi1.95Pb0.05Te3 exhibit p-type conduction with enhanced ZT of similar to 0.63 at 386 K. The conversion efficiency of Bi1.95Pb0.05Te3 based single thermoelement with hot pressed Ni/Ag electrical contacts was found to be similar to 4.9% for a temperature difference (Delta T) of 200 K. The efficiency was further enhanced to similar to 12% (at Delta T similar to 494 K) in the segmented thermoelement consisting of Bi1.95Pb0.05Te3 and (AgSbTe2)(0.15)(GeTe)(0.85) (i.e. TAGS-85)
Single layer graphene: an alternative electrode material for ferroelectric liquid crystal based displays
No full textWe made comparative investigations on indium tin oxide (ITO) and single-layer graphene (SLG)-coated glass substrate as electrodes, specially for ferroelectric liquid crystal (FLC)-based system. We experimentally examined the comparative behaviour of important electro-optical FLC parameters for ITO- and SLG-based sample cells. The parameters are observed to be almost similar for both the cells. Interestingly, the value of threshold voltage is observed lower in SLG-based cell in comparison to that of conventional ITO/ITO cell. The presented results will definitely add a step to prove the suitability of graphene to be used as transparent electrodes in FLC-based display devices
Large bandgap reduced graphene oxide (rGO) based n-p(+) heterojunction photodetector with improved NIR performance
No full textIntegration of two-dimensional reduced graphene oxide (rGO) with conventional Si semiconductor offers novel strategies for realizing broadband photodiode with enhanced device performance. In this quest, we have synthesized large bandgap rGO and fabricated metal-free broadband (300-1100 nm) back-to-back connected np-pn hybrid photodetector utilizing drop casted n-rGO/p(+)-Si heterojunctions with high performance in NIR region (830 nm). With controlled illumination, the device exhibited a peak responsivity of 16.7 AW(-1) and peak detectivity of 2.56 x 10(12) Jones under 830 nm illumination (11 mu Wcm(-2)) at 1 V applied bias with fast response (similar to 460 mu s) and recovery time (similar to 446 mu s). The fabricated device demonstrated excellent repeatability, durability and photoswitching behavior with high external quantum efficiency (similar to 2.5 x 10(3)%), along with ultrasensitive behavior at low light conditions