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Amorphous YCrO3 (YCO) films were prepared on Pt/TiO2/SiO2/Si substrate by pulsed laser deposition in order to investigate resistive switching (RS) phenomenon. The Pt/YCO/Pt device showed stable unipolar RS with resistance ratio of ∼105 between low and high resistance states, excellent endurance and retention characteristics, as well as, non-overlapping switching voltages with narrow dispersions. Based on the x-ray photoelectron spectroscopy and temperature dependent switching characteristics, observed RS was mainly ascribed to the oxygen vacancies. Moreover, current-voltage characteristics of the device in low and high resistance states were described by Ohmic and trap controlled space-charge limited conduction mechanisms, respectively. [ABSTRACT FROM AUTHOR]

We report the crystal structure, dielectric, transport, and magnetic properties of Ni0.65Zn0.35Fe2O4. Rietveld refinement results of X-ray diffraction patterns confirm the phase formation of the material with cubic crystal structure (Fd3m). The frequency dependent ac conductivity behavior obeys the Jonscher's power law and is explained using the jump relaxation model. The observed behavior of temperature dependent bulk conductivity is attributed to the variable-range hopping of localized polarons. The correlation of polaron conduction and high permittivity behavior of NZFO is established on the basis of long range and short range conduction mechanisms. The complex impedance spectra clearly show the contribution of both grain and grain boundary effect on the electrical properties. [ABSTRACT FROM AUTHOR]

Forming free and thermally stable bipolar resistive switching behavior was observed in the memory devices composed of graphene oxide (GO) thin films on ITO coated glass substrate with Platinum (Pt) as the top electrode. The switching between the low resistance state and high resistance state showed a reliable and repeating behavior with an on/off ratio of 104 at room temperature. The Pt/GO/ITO device showed metallic and semiconducting characteristics in low and high resistance states, respectively, when resistance was measured as a function of temperature. Ohmic conduction was found to dominate in all regions of switching operation except for the high voltage regime of high resistance state where space charge limited conduction was found to be the main mechanism of current conduction. The device showed good endurance up to 104 s and retention characteristics up to 100 cycles with on/off ratio ∼104. The switching mechanism was found to be governed by migration of oxygen between GO layer and bottom ITO electrode, which was further confirmed by Raman Spectroscopy. The device exhibited stable bipolar switching characteristics with good retention and endurance properties at high temperatures up to 500 K. The graphene oxide based memory devices fabricated by simple chemical method have potential in the field of nonvolatile memory applications well above the room temperature. [ABSTRACT FROM AUTHOR]

A self-powered UV sensor with high responsivity was developed by coupling ZnO based piezoelectric nanogenerator and photodetector for uninterrupted real-time monitoring of UV radiation. Unlike conventional UV photodetectors, our approach couples a ZnO based metal-semiconductor-metal photodetector as a variable load resistor with a flexible ZnO:PVDF piezoelectric nanogenerator through impedance matching to realize self-powering of photodetector. The as fabricated UV photodetector exhibits a dark resistance of approximately 55 MΩ and change of resistance from 12 to 2 MΩ in response to UV illumination ranging from 1.5 to 14.5 mW/cm2. Under UV exposure of 1.5 mW/cm2, the output voltage of self-powered UV sensor drops from ∼14.6 V (dark) to ∼3.88 V. With increasing UV intensity from 1.5 to 14.5 mW/cm2, the output voltage gradually decreases from ∼3.88 to ∼1.04 V due to reduced ZnO photodetector resistance. This self-powered UV sensor exhibits excellent performance with a sensitivity of ∼93%, a voltage responsivity of 7.14 V (mW−1 cm−2), a response time of 0.67 s, and a recovery time of 4 s, which are better than the previous reports. The environmentally stable and biocompatible nature of ZnO based system makes it a promising candidate for self-powered real time ultraviolet remote sensing applications. [ABSTRACT FROM AUTHOR]

We report the switchable photovoltaic effects in graphene/BiFeO3/Pt heterostructures. Pure phase polycrystalline BiFeO3 films were deposited on Pt/TiO2/SiO2/Si substrates by pulse laser deposition. A bilayer graphene was transferred onto the BiFeO3 film which serves as transparent conducting electrodes. The heterostructures showed switchable photovoltaic effect depending on ferroelectric polarization directions indicating depolarization field induced separation of photogenerated carriers. The open circuit voltage (VOC) and short circuit current density (JSC) were measured to be ~ 110 mV, ~92 μA/cm² in positive polarity and similar values were obtained when the polarity was reversed. The JSC and VOC also showed rapid response (< 100 ms) as a function of light exposure time. [ABSTRACT FROM AUTHOR]

Multilevel resistive switching was observed in random access memory device using amorphous SmGdO3 (SGO) ternary oxide thin films. Non-volatile and stable 4-level resistance states with sufficient margin of resistance ratios were observed by varying compliance current which was attributed to compliance current dependent variation in size of conducting filaments. As fabricated Pt/SGO/Pt devices exhibited excellent switching parameters such as stable resistance ratios of reset (ON) to set (OFF) states, non-overlapping switching voltages, excellent data retention, and endurance. Temperature dependent variation of resistances of ON and OFF states of the device was studied to elucidate current conduction and resistive switching mechanisms. [ABSTRACT FROM AUTHOR]

Maxwell–Wagner relaxation dominated Al2O3/TiO2 nanolaminates (ATA NLs) have recently demonstrated their potential for high-density energy storage applications. In this report, we have unraveled the defect-mediated transport mechanisms prevailing in Al2O3/TiO2 sub-nanometric laminates. Temperature-dependent ac conductivity measurements revealed the signature of small polaron hopping in TiO2 active layers and trap-assisted tunneling transport through Al2O3 barrier layers, which was corroborated by resonant photoelectron spectroscopy and temperature-dependent current–voltage measurement. The polaronic defect states, found ∼1 eV below the Fermi level, served as the hopping centers and leakage paths for current. The signature of quantum tunneling transport and the negative differential conductance observed toward higher electric field was attributed to the splitting of delocalized minibands. These transport properties of Al2O3/TiO2 nanolaminates will help in tailoring these materials for next-generation storage capacitors. [ABSTRACT FROM AUTHOR]

We report the photovoltaic properties of doped ferroelectric [Bi0.9La0.1][Fe0.97Ti0.02Zr0.01]O3 (BLFTZO) thin films. Polycrystalline BLFTZO films were fabricated on Pt/TiO2/SiO2/Si substrates by pulsed laser deposition technique. Al-doped ZnO transparent top electrodes complete the ZnO:Al/BLFTZO/Pt metal-ferroelectric-metal capacitor structures. BLFTZO showed switchable photoresponse in both polarities. The open circuit voltage (VOC) and short circuit current (JSC) were found to be ~0.022 V and ~650 μA/cm², respectively after positive poling, whereas significant difference in VOC ~ 0.018V and JSC ~ 700 μA/cm² was observed after negative poling. The observed switchable photocurrent and photovoltage responses are explained on the basis of polarization flipping in BLFTZO due to the applied poling field. [ABSTRACT FROM AUTHOR]

With the rapid development of new device miniaturization technology, there is invigorated interest in magnetic nanostructures for potential application in novel multifunctional devices. In continuation to our search for a suitable magnetic material having Curie temperature (Tc) well above room temperature for multifunctional applications, we have studied the dielectric, optical, magnetic, and resistance switching characteristics of Ni0.65Zn0.35Fe2O4 (NZFO) thin films. The observation of only (004) reflection in the X-ray diffraction patterns confirms the c-axis orientation and high quality growth of NZFO thin films. The presence of mixed valences of Fe2+/Fe3+ cations is probed by X-ray photon spectroscopy, which supports the cationic ordering-mediated large dielectric response. Our investigations reveal NZFO to be an indirect band gap material (~1.8eV) with a direct gap at ~2.55eV. These nanostructures exhibit high saturation magnetization and a low coercive field with a ferrimagnetic-paramagnetic phase transition of ~713K. Magnetic force microscopy studies revealed the stripe-like domain structure of the investigated thin films. In addition, these thin films exhibit reliable and repeatable unipolar resistive switching characteristics. The observed high dielectric permittivity with low loss tangent, large magnetization with soft magnetic behavior, striped magnetic domain structure and reliable resistance switching in NZFO thin films above room temperature suggest potential application in memory, spintronics, and multifunctional devices. [ABSTRACT FROM AUTHOR]

High-pressure synchrotron based angle dispersive x-ray diffraction (ADXRD) studies were carried out on SmGdO3 (SGO) up to 25.7 GPa at room temperature. ADXRD results indicated a reversible pressure-induced phase transition from ambient monoclinic to hexagonal phase at ∼8.9 GPa. The observed pressure-volume data were fitted with the third order Birch-Murnaghan equation of state yielding zero pressure bulk modulus Bo=132(22) and 177(9) GPa for monoclinic (B-type) and hexagonal (A-type) phases, respectively. Pressure dependent micro-Raman spectroscopy further confirmed the monoclinic to hexagonal phase transition at about 5.24 GPa. The mode Grüneisen parameters and pressure coefficients for different Raman modes corresponding to each individual phases of SGO were calculated using pressure dependent Raman mode analysis. [ABSTRACT FROM AUTHOR]

We report magnetoelectric coupling and Raman spectroscopic studies on [(1 - x)Pb(Fe0.5Nb0.5) O3-xNi0.65Zn0.35Fe2O4] (x=0.20) PFN-NZFO composite. Apart from the presence of zone centre Raman active modes of the parent compound, some new peaks are observed in the low frequency region. The electric field controlled peak position (∼48 cm-1) suggests that this mode is of magnetic origin. From temperature dependent Raman scattering studies, temperature coefficients for phonons of different symmetries were estimated. Our measurements on electrical control of magnetic order and magnetic control of electrical order confirmed the existence of converse and direct magnetoelectric coupling in this composite at room temperature. [ABSTRACT FROM AUTHOR]

We report unipolar resistive switching suitable for nonvolatile memory applications in polycrystalline BiFeO3 thin films in planar electrode configuration with nonoverlapping Set and Reset voltages, On/Off resistance ratio of ~104 and good data retention (verified for up to 3,000 s). We have also observed photovoltaic response in both high and low resistance states, where the photocurrent density was about three orders of magnitude higher in the low resistance state as compared to the high resistance state at an illumination power density of ~100 mW/cm². Resistive switching mechanisms in both resistance states of the planar device can be explained by using the conduction filament (thermo-chemical) model. [ABSTRACT FROM AUTHOR]

Lanthanum hexaboride films have been deposited on a tungsten tip by pulsed laser deposition technique. The field emission studies have been performed in the conventional field emission geometry. The Fowler-Nordheim plot obtained from the current-voltage characteristic is found to be linear in accordance with the quantum mechanical tunneling phenomenon. A current density of 1.2×104 A/cm2 is drawn from the deposited tip. The field enhancement factor is calculated to be 5537 cm-1, indicating that the field emission is from nanoscale protrusions present on emitter surface. The emission current-time plots show the very good stability of the emitter. [ABSTRACT FROM AUTHOR]