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Unipolar resistive switching in sol-gel synthesized strontium titanate thin films
No full textWe report repeatable and robust unipolar resistive switching (URS) in strontium titanate (SrTiO3 similar to STO) thin films fabricated on conducting ITO coated glass substrate. The Atomic Force Microscopy (AFM) image of the top surface of the films suggests very smooth surface over a large area. The conduction mechanisms responsible for the resistive switching phenomenon were also thoroughly analyzed by current-voltage and impedance spectroscopy analysis. Frequency-dependent various impedance parameters were analyzed for each resistive states (high resistance state (HRS) and low resistive state (LRS)). The oxygen vacancies may be one of the dominating factors for robust URS phenomenon in the device. The presented Au/STO/ITO memory devices have exhibited long retention characteristics of >10(4) s and OFF/ON resistance ratio of >10(3) with a distinguishable SET and RESET voltage window of similar to 1 V
High field (up to 140 kOe) angle dependent magneto transport of Bi2Te3 single crystals
No full textWe report the angle dependent high field (up to 140 kOe) magneto transport of Bi2Te3 single crystals, a well-known topological insulator. The crystals were grown from melt of constituent elements via solid state reaction route by self-flux method. Details of crystal growth along with their brief characterisation up to 5 Tesla applied field was reported by some of us recently (Sultana et al 2017 J. Magn. Magn. Mater. 428 213). The angle dependence of the magneto-resistance (MR) of Bi2Te3 follows the cos (theta) function i.e., MR is responsive, when the applied field is perpendicular (tilt angle theta = 0 degrees and/or 180 degrees) to the transport current. The low field (+/- 10 kOe) MR showed the signatures of weak anti localisation character with typical nu-type cusp near origin at 5 K. Further, the MR is linear right up to highest applied field of 140 kOe. The large positive MR are observed up to high temperatures and are above 250% and 150% at 140 kOe in perpendicular fields at 50 K and 100 K respectively. Heat capacity C-P (T) measurements revealed the value of Debye temperature ((sic)D) to be 135 K. Angle resolved photoemission spectroscopy data clearly showed that the bulk Bi2Te3 single crystal consists of a single Dirac cone
Non-approximated series resistance evaluation by considering high ideality factor in organic solar cell
Get PDFThe quality performance analysis of any solar cell can only be predicted through the parameters extracted from its current-voltage characteristics. Herein, we demonstrate an efficient analytical method to calculate the series resistance of organic solar cells without any pre approximation. It has been shown that the inaccuracy in series resistance takes place due to the high ideality factor of the organic based solar cells, usually ranging from 2-5. Using a systemic approach, we solved the single diode solar cell model to determine the series resistance expression. The dependence of series resistance on ideality factor of the device and the reverse saturation current calculation through the illuminated current-voltage characteristics has been presented here for the first time. The entire method has been programmatically realized in MAT-LAB. The extracted parameters values have been compared to the other methods for the proof of validation and it shows good agreement where as some outputs are better resolved. Additionally, the effectiveness of the present method is also matched with NREL certified silicon solar cell (reference cell model 60623) parameter extracted from K24XX cell software provided with PET cell tester model, CT200AAA solar simulators. The present proposed method is not restricted to the organic solar cell only but it can also be applied for the other type of solar cell as well. Therefore, the proposed method shows the relevance in the present scenario of solar cell research and development
Distinction between double electromagnetically induced transparency and double Autler-Townes splitting in RF-driven four-level ladder Rb-87 atomic vapor
No full textIn this paper, the physical origin of interferences has been explored in a four-level cascade rubidium atom by simultaneous interaction with three energies; two optical fields and one radio frequency (RF) field. The atomic system is investigated by a combination of the analytical method introduced by Zhu et al (2010 Phys. Rev. A 81 053836) and resonant pole method introduced by Anisimov (2008 J. Mod. Opt. 55). A substantial amount of variation in the probe absorption has been observed in various regimes. The transition from electromagnetically induced transparency (EIT) to Autler-Townes spitting (ATS) is observed. It is found that a definite threshold value exists governing the crossover from EIT to ATS. The applied analytical method gives a clear insight into the nature of interferences; one may observe EIT as a consequence of destructive interference, whereas ATS is a consequence of constructive interference. Furthermore, a transition from single EIT to double electromagnetically induced transparency has been detected when the system is illuminated by RF-driving field in weak control regime. Further, transition from ATS to double Autler-Townes splitting has been observed in the strong control regime
Effect of HfO2 nitridation on structural, optical and electrical properties of GaN films grown on HfO2/Si(100) by laser molecular beam epitaxy
No full textGrowth of high quality III-nitride films on high-k oxide/Si substrates is crucial for the fabrication of nitride based metal-oxide-semiconductor devices. Here, we report the effect of nitridation of HfO2 surface on the physical properties of gallium nitride (GaN) films grown on HfO2 (5 nm)/p-Si(100) substrates using laser molecular beam epitaxy (LMBE) technique. The grazing incidence x-ray diffraction (GIXRD) measurements showed the prominent GaN growth along (0002) direction. It is observed that the HfO(2 )nitridation significantly improves the surface coverage of GaN film with larger grains of size in the range 200 similar to 250 nm. Room temperature photoluminescence (PL) spectroscopy exhibits a sharp, intense near band-edge emission line at 3.4 eV with negligible defect-related deep bands for the GaN film grown with HfO2 nitridation. Also, the current-voltage characteristics of Au/ GaN Schottky contacts show a reduced leakage current for HfO2 nitridation. Thus, the surface nitridation of HfO2 is found vital to improve the quality of GaN films for the development of GaN-on-Si technology
Effect of magnetic fullerene on magnetization reversal created at the Fe/C-60 interface
Get PDFProbing the hybridized magnetic interface between organic semiconductor (OSC) and ferromagnetic (FM) layers has drawn significant attention in recent years because of their potential in spintronic applications. Recent studies demonstrate various aspects of organic spintronics such as magnetoresistance, induced interface moment etc. However, not much work has been performed to investigate the implications of such OSC/FM interfaces on the magnetization reversal and domain structure which are the utmost requirements for any applications. Here, we show that non-magnetic Fullerene can obtain non-negligible magnetic moment at the interface of Fe(15 nm)/C-60(40 nm) bilayer. This leads to substantial effect on both the magnetic domain structure as well as the magnetization reversal when compared to a single layer of Fe(15 nm). This is corroborated by the polarized neutron reflectivity (PNR) data which indicates presence of hybridization at the interface by the reduction of magnetic moment in Fe. Afterwards, upto 1.9 nm of C-60 near the interface exhibits magnetic moment. From the PNR measurements it was found that the magnetic C-60 layer prefers to be aligned anti-parallel with the Fe layer at the remanant state. The later observation has been confirmed by domain imaging via magneto-optic Kerr microscopy
Effect of multiband transport on charge carrier density fluctuations at the LaAlO3/SrTiO3 interface
No full textMultiband transport in superconductors is interesting both from an academic as well as an application point of view. It has been postulated that interband scattering can significantly affect the carrier dynamics in thesematerials. In this articlewe present a detailed study of the electrical transport properties of the high-mobility two-dimensional electron gas residing at the interface of LaAlO3/SrTiO3, a prototypical multiband superconductor. We show, through careful measurements of the gate dependence of the magnetoresistance and resistance fluctuations at ultralow temperatures, that transport in the superconducting regime of this system has contributions from two bands which host carriers of very different characters. We identify a gate-voltage tunable Lifshitz transition in the system and show that the resistance fluctuations have strikingly different features on either side of it. At low carrier densities, resistance noise is dominated by number-density fluctuations arising from trapping-detrapping of charge carriers from defects in the underlying SrTiO3 substrate, characteristic of a single-band semiconductor. Above the Lifshitz transition, the noise presumably originates from interband scattering. Our paper highlights the importance of interband scattering processes in determining the transport properties of low-dimensional systems and projects resistance fluctuation spectroscopy as a viable technique for probing the charge carrier dynamics across a Lifshitz transition
Effect of Ethylene Glycol Doping on Performance of PEDOT: PSS/mu T-n-Si Heterojunction Solar Cell
No full textThis study reports effect of co-solvent doping in poly (3, 4-ethyelenedioxythiophene): poly(dimethyl sulfoxide) (PEDOT: PSS) over the performance of Ag/PEDOT: PSS/mu T-n-Si/In: Ga architecture based solar cell. PEDOT: PSS polymer is doped with varying concentration of ethylene glycol (EG). At 10% (volume) concentration performance of the device is highest with 4.69% power conversion efficiency. At higher or lower concentrations of ethylene glycol device performance deteriorates with sharp decline in short-circuit current density. Improvement in conductivity of the PEDOT: PSS polymer due to addition of co-solvent is the reason behind improvement in the performance of the device efficiency
Evaluation of uncertainty of measurement of shadow mask dot pitch using different approaches
No full textThe present paper discusses procedure for uncertainty of measurement evaluation in an experimental investigation to measure shadow mask dot pitch using laser interferometry. Here, we discuss evaluation of uncertainty of measurement in accordance to Law of propagation of uncertainties (GUM/LPU) and Monte Carlo Simulation (MCS) approaches. MCS has been recognized as an alternative approach to LPU in guide to measurement uncertainties (GUM) for evaluation of uncertainty of measurement and other related applications. A comparison of findings of GUM/LPU and MCS is made, which appears to be in good agreement. The present study attempts to investigate the suitability of MCS for evaluation of measurement of uncertainty in case of shadow mask dot pitch and reveals the significance of MCS in this regard
Fabrication of sensitive bioelectrode based on atomically thin CVD grown graphene for cancer biomarker detection
No full textMotivation behind the present work is to fabricate a cost effective and scalable biosensing platform for an easy and reliable detection of cancer biomarker Carcinoembryonic antigen (CEA). Here, we report the sensitive and selective detection of CEA using graphene based bio-sensing platform. Large sized (similar to 2.5 x 1.0 cm(2)), uniform, continuous, single and few layers graphene films have been grown on copper (Cu) substrate employing chemical vapor deposition (CVD) technique using hexane as a liquid precursor. Functional group has been created over Graphene/Cu substrate through pi-pi stacking of 1-pyrenebutanoic acid succinimidyl ester (PBSE). Further, to make the sensor specific to CEA, antibody of CEA (anti-CEA) has been covalently immobilized onto PBSE/Graphene/Cu electrode. Selective and sensitive detection of CEA is achieved by anti-CEA/PBSE/Graphene/Cu electrode through electrochemical impedance spectroscopy (EIS) measurements. Under optimal condition, the fabricated sensor shows linear response in the physiological range 1.0-25.0 ng mL(-1) (normal value similar to 5.0 ng mL(-1)), revealing sensitivity 563.4 Omega ng(-1) mL cm(-2) with a correlation coefficient of 0.996 and limit of detection (LOD) 0.23 ng mL(-1). In this way, one step electrode fabrication with high specific surface area provides a light weight, low cost, reliable and scalable novel biosensing platform for sensitive and selective detection of CEA. We believe that this bioelectrode equipped with specific recognition elements could be utilized for detection of other biomolecules too