Non-ohmic conduction and electrical switching under pressure of the charge transfer complexo-tolidine-iodine

The current voltage characteristics ofo-tolidine-iodine, with stoichiometry 1:1 grown from benzene, have been studied under high pressures upto 6 GPa atT=300 K andT=77 K. The characteristics show a pronounced deviation from ohmicity beyond a certain current for all pressures studied. At room temperature, beyond a threshold field the system switches from a low conductingOFF state to a high conductingON state with σON/σOFF ∼ 103. TheOFF state can be restored by the application of an a.c. pulse of low frequency. The temperature dependence of the two states studied indicates that theOFF state is semiconducting while theON state, beyond a certain applied pressure is metallic. The characteristics atT=77 K do not show any switching.

Negative differential resistance in GaN nanocrystals above room temperature

Negative differential resistance (NDR) has been observed for the first time above room temperature in gallium nitride nanocrystals synthesized by a simple chemical route. Current-voltage characteristics have been used to investigate this effect through a metal-semiconductor-metal (M-S-M) configuration on SiO2. The NDR effect is reversible and reproducible through many cycles. The threshold voltage is similar to 7 V above room temperature.

Some investigations on secondary breakdown in p-n junctions considering the effect of thermally generated carriers

The V-I characteristic of a p-n junction under breakdown is calculated taking the thermally generated carriers into account. The current density distributions computed under different conditions have been given. The light emission and other characteristics reported by Chiang and Lauritzen and others have been explained.

In-situ one-step hydrothermal synthesis of a lead germanate-graphene composite as a novel anode material for lithium-ion batteries

Lead germanate-graphene nanosheets (PbGeO3-GNS) composites have been prepared by an efficient one-step, in-situ hydrothermal method and were used as anode materials for Li-ion batteries (LIBs). The PbGeO3 nanowires, around 100–200 nm in diameter, are highly encapsulated in a graphene matrix. The lithiation and de-lithiation reaction mechanisms of the PbGeO3 anode during the charge-discharge processes have been investigated by X-ray diffraction and electrochemical characterization. Compared with pure PbGeO3 anode, dramatic improvements in the electrochemical performance of the composite anodes have been obtained. In the voltage window of 0.01–1.50 V, the composite anode with 20 wt.% GNS delivers a discharge capacity of 607 mAh g−1 at 100 mA g−1 after 50 cycles. Even at a high current density of 1600 mA g−1, a capacity of 406 mAh g−1 can be achieved. Therefore, the PbGeO3-GNS composite can be considered as a potential anode material for lithium ion batteries.

Aqueous colloidal stability evaluated by zeta potential measurement and resultant TiO2 for superior photovoltaic performance

Controlling the morphological structure of titanium dioxide (TiO 2) is crucial for obtaining superior power conversion efficiency for dye-sensitized solar cells. Although the sol-gel-based process has been developed for this purpose, there has been limited success in resisting the aggregation of nanostructured TiO2, which could act as an obstacle for mass production. Herein, we report a simple approach to improve the efficiency of dye-sensitized solar cells (DSSC) by controlling the degree of aggregation and particle surface charge through zeta potential analysis. We found that different aqueous colloidal conditions, i.e., potential of hydrogen (pH), water/titanium alkoxide (titanium isopropoxide) ratio, and surface charge, obviously led to different particle sizes in the range of 10-500 nm. We have also shown that particles prepared under acidic conditions are more effective for DSSC application regarding the modification of surface charges to improve dye loading and electron injection rate properties. Power conversion efficiency of 6.54%, open-circuit voltage of 0.73 V, short-circuit current density of 15.32 mA/cm2, and fill factor of 0.73 were obtained using anatase TiO 2 optimized to 10-20 nm in size, as well as by the use of a compact TiO2 blocking layer.

Space-charge limited conduction in doped polypyrrole devices

Doping dependent current-voltage (I-V) and capacitance-voltage (C-V) measurements were carried out on polypyrrole devices in metal-polymer-metal sandwich structure. Temperature dependent I-V measurements infer that space-charge limited conduction (SCLC) with exponential trap distribution is appropriate for the moderately doped samples, whereas trap-free SCLC is observed in lightly doped samples. Trap densities and energies are estimated, the effective mobility is calculated using the Poole-Frenkel model, and the mobility exhibits thermally activated behavior. Frequency dependent capacitance-voltage characteristics show a peak near zero bias voltage, which implies that these devices are symmetric with a negligible barrier height at the metal-polymer interface. Low frequency capacitance measurements have revealed a negative capacitance at higher voltages due to the processes associated with the injection and redistribution of space-charges. (C) 2010 American Institute of Physics.

Heteroepitaxial Yba2cu3o7-X-Prba2cu3o7-X-Yba2cu3o7-X Weak Links Grown By Laser Deposition

Summary form only given. The authors have developed a controllable HTSC (high-temperature superconductor) weak-link fabrication process for producing weak links from the high-temperature superconductor YBa2Cu3O7-x (YBCO), using PrBa2Cu3O7-x (PBCO) as a lattice-matched semiconducting barrier layer. The devices obtained show current-voltage characteristics similar to those observed for low-temperature superconductor/normal-metal/superconductor (SNS) devices. The authors found good scaling of the critical currents Ic with area, A, and scaling of the resistances Rj with 1/A; the typical values of the IcRj product of 3.5 mV are consistent with traditional SNS behavior. The authors observed Shapiro steps in response to 100-GHz millimeter-wave radiation and oscillation of the DC supercurrent in a transverse magnetic field, thus demonstrating that both the AC and DC Josephson effects occur in these devices.

Varistors based on polycrystalline ZnO:Cu

Sintered, polycrystalline ZnO ceramics with copper as the only additive exhibit highly nonlinear current‐voltage characteristics. Increasing nonlinearity index (α=4–45) with Cu concentration of 0.01–1 mol % is also variable with respect to ceramic processing methods. Incorporation of Cu in the ZnO lattice is indicated from the electron probe microanalysis and the photoluminescence spectra. Cu acceptors are compensated by holes in the grain boundary layers, whereas the concentration of intrinsic donors is higher in the grain interior. The presence of positive charges leads to thinning of the depletion region, resulting in nonlinear characteristics.

Microstructure related influence on the electrical properties of pulsed laser ablated (Ba, Sr)TiO3 thin films

The microstructural dependence of electrical properties of (Ba, Sr)TiO3(BST) thin films were studied from the viewpoint of dc and ac electrical properties. The films were grown using a pulsed laser deposition technique in a temperature range of 300 to 600 degrees C, inducing changes in grain size, structure, and morphology. Consequently, two different types of films were realized, of which type I, was polycrystalline, multigrained, while type II was [100] oriented possessing a densely packed fibrous microstructure. Leakage current measurements were done at elevated temperatures to provide evidence of the conduction mechanism present in these films. The results revealed a contribution from both electronic and ionic conduction. In the case of type I films, two trapping levels were identified with energies around 0.5 and 2.73 eV, which possibly originate from oxygen vacancies V-O and Ti3+ centers, respectively. These levels act as shallow and deep traps and are reflected in the current-voltage characteristics of the BST thin films. The activation energy associated with oxygen vacancy motion in this case was obtained as 1.28 eV. On the contrary, type II films showed no evidence of deep trap energy levels, while the identified activation energy associated with shallow traps was obtained as 0.38 eV. The activation energy obtained for oxygen vacancy motion in type II films was around 1.02 eV. The dc measurement results were further elucidated through ac impedance analysis, which revealed a grain boundary dominated response in type I in comparison to type II films where grain response is highlighted. A comparison of the mean relaxation time of the two films revealed three orders of magnitude higher relaxation time in the case of type I films. Due to smaller grain size in type I films the grains were considered to be completely depleted giving rise to only grain boundary response for the bulk of the film. The activation energy obtained from conductivity plots agree very well with that of dc measurements giving values 1.3 and 1.07 eV for type I and type II films, respectively. Since oxygen vacancy transport have been identified as the origin of resistance degradation in BST thin films, type I films with their higher value of activation energy for oxygen ion mobility explains the improvement in breakdown characteristics under constant high dc field stress. The role of microstructure in controlling the rate of degradation is found useful in this instance to enhance the film properties under high electric field stresses. (C) 2000 American Institute of Physics. [S0021-8979(00)00418-7].

Superconducting gap in Nb seen by point contact spectroscopy

The nonlinear current voltage characteristics of a point contact convey information about various excitations in the metal. We have made a poin~ contact study on a superconductor to see the band gap and on a normal metal to see Ihe transport characteristics.

Spectroscopic and electrical properties of SiO2 films prepared by simple and cost effective sol-gel process

Amorphous SiO2 thin films were prepared on glass and silicon substrates by cost effective sol-gel method. Tetra ethyl ortho silicate (TEOS) was used as the precursor material, ethanol as solvent and concentrated HCl as a catalyst. The films were characterized at different annealing temperatures. The optical transmittance was slightly increased with increase of annealing temperature. The refractive index was found to be 1.484 at 550 nm. The formation of SiO2 film was analyzed from FT-IR spectra. The MOS capacitors were designed using silicon (1 0 0) substrates. The current-voltage (I-V), capacitance-voltage (C-V) and dissipation-voltage (D-V) measurements were taken for all the annealed films deposited on Si (1 0 0). The variation of current density, resistivity and dielectric constant of SiO2 films with different annealing temperatures was investigated and discussed for its usage in applications like MOS capacitor. The results revealed the decrease of dielectric constant and increase of resistivity of SiO2 films with increasing annealing temperature. (C) 2010 Elsevier B.V. All rights reserved.

Structural and electrical properties of radio frequency magnetron sputtered tantalum oxide films: Influence of post-deposition annealing

The as-deposited and annealed radio frequency reactive magnetron sputtered tantalum oxide (Ta2O5) films were characterized by studying the chemical binding configuration, structural and electrical properties. X-ray photoelectron spectroscopy and X-ray diffraction analysis of the films elucidate that the film annealed at 673 K was stoichiometric with orthorhombic beta-phase Ta2O5. The dielectric constant values of the tantalum oxide capacitors with the sandwich structure of Al/Ta2O5/Si were in the range from 14 to 26 depending on the post-deposition annealing temperature. The leakage current density was < 20 nA cm(-2) at the gate bias voltage of 0.04 MV/cm for the annealed films. The electrical conduction mechanism observed in the films was Poole-Frenkel. (C) 2010 Elsevier Ltd. All rights reserved.

Preparation and characterization of multiwall carbon nanotube/polypyrrole coaxial fibrils

Multiwall carbon nanotube (MWNT)/polypyrrole (PPy) fibrils were fabricated by template-free in situ electrochemical deposition of PPy over MWNTs, and characterized by electron microscopy and electrical measurements. Scanning and transmission electron microscopy studies reveal that PPy coating on the surface of nanotube is quite uniform throughout the length, with the possibility of forming unique Y-junctions. Current (I)-voltage (V) characteristics at various temperatures show nonlinearity due to tunneling and hopping contributions to transport across the barriers. AC conductivity measurements (300-4.2 K) show that the onset frequency scales with temperature, and the nanoscale connectivity in MWNT/PPy fibrils decreases with the lowering of temperature. (C) 2011 Elsevier B.V. All rights reserved.

Study of the electrical properties of pulsed laser ablated (Ba0.5Sr0.5)TiO3 thin films

The laser ablated barium strontium titanate (BST) thin films were characterized in terms of composition, structure, microstructure and electrical properties. Films deposited at 300 degrees C under 50 mTorr oxygen pressure and 3 J cm(-2) laser fluence and further annealed at 600 degrees C in flowing oxygen showed a dielectric constant of 467 and a dissipation factor of 0.02. The room-temperature current-voltage characteristics revealed a space charge limited conduction (SCLC) mechanism, though at low fields the effect of the electrodes was predominant. The conduction mechanism was thoroughly-investigated in terms of Schottky emission at low fields, and bulk-limited SCLC at high fields. The change over to the bulk-limited conduction process from the electrode-limited Schottky emission was, attributed to the process of tunneling through the electrode interface at high fields resulting into the lowering of the electrode contact resistance and consequently giving rise to a bulk limited conduction process. The predominance of SCLC mechanism in the films suggests that the bulk properties are only revealed if the depletion width at the electrode interface is thin enough to allow the tunneling process to take place. This condition is only favorable if the him thickness is high or if the doping concentration is high enough. In the present case the film thickness ranged from 0.3 to 0.7 mu m which was suitable to show the transition mentioned above. (C) 1999 Elsevier Science S.A. All rights reserved.

Electrical characterization of Ba(Zr0.1Ti0.9)O-3 thin films grown by pulsed laser ablation technique

In situ annealed thin films of ferroelectric Ba(Zr0.1Ti0.9)O-3 were deposited on platinum substrates by pulsed laser ablation technique. The as grown films were polycrystalline in nature without the evidence of any secondary phases. The polarization hysteresis loop confirmed the ferroelectricity, which was also cross-checked with the capacitance-voltage characteristics. The remnant polarization was about 5.9 muC cm(-2) at room temperature and the coercive field was 45 kV. There was a slight asymmetry in the hysteresis for different polarities, which was thought to be due to the work function differences of different electrodes. The dielectric constant was about 452 and was found to exhibit low frequency dispersion that increased with frequency, This was related to the space-charge polarization. The complex impedance was plotted and this exhibited a semicircular trace, and indicated an equivalent parallel R - C circuit within the sample. This was attributed to the grain response. The DC leakage current-voltage plot was consistent with the space-charge limited conduction theory, but showed some deviation, which was explained by assuming a Poole-Frenkel type conduction to be superimposed on to the usual space-charge controlled current. (C) 2002 Elsevier Science B.V. All rights reserved.