Evidence for unpinned magnetic flux vortices above theIctransition in the 2223-phase high-Tcsuperconductor

A similarity in the dc voltage-current (V-I) curves for both direct and alternating transport currents is used to propose that unpinned flux vortices are generated above theI _ctransition for dc transport currents, when Abrikosov flux vortices begin to penetrate the superconductor. Two methods can be used to give a dc voltage drop for an ac transport current: (1) if there is a slight dc offset voltage in the ac current which favors vortex loop collapse as in a traditional dcI _ctest, or (2) if an asymmetric transverse magnetic field is present which favors vortex loop collapse for current in one direction over the reverse direction.     

The role of the HfO2–TiN interface in capacitance–voltage nonlinearity of Metal-Insulator-Metal capacitors

The high-k Metal-Insulator-Metal (MIM) capacitor Back-End-of-Line (BEOL) integration into mixed signal and Radio Frequency (RF) circuits is characterized by the effort toward optimizing the capacitance voltage linearity. This letter is focused on the role of the TiO_xN_y-based interfacial layer with respect to Capacitance–Voltage C(V) curves of Au/HfO₂/TiN MIM capacitors. The correlation between the quadratic capacitance–voltage variation and interfacial layer thickness is demonstrated. The quadratic voltage coefficient of the dielectric stack can be reduced by increasing the thickness of the TiO_xN_y layer.     

Non-exponential photocurrent growth and decay in Safranine-T dye doped solid state polymer photoelectrochemical cell

In the present communication photoconductivity has been studied in Safranine-T dye doped solid state polymer photoelectrochemical cell (PEC). The cell contains a blend made of Safranine-T dispersed in polyvinyl alcohol (PVA), polyethylene oxide (PEO) complexed with ammonium perchlorate (NH₄ClO₄), ethylene carbonate (EC) and propylene carbonate (PC). A thin layer of this blend is sandwiched between two ITO coated glass plate electrodes. The photoresponse is observed in our system illuminated by a tungsten lamp in presence of an external bias voltage. Photocurrent changes with the applied bias voltage and the typical change is about 1.68 A for a device area of 0.64 cm² at a bias voltage of 1.5 V and at an incident intensity of about 40 mW/cm² which indicates a sensitivity of $0.66 × 10^–4 A/W. In the present work the dark current–voltage (I-V) characteristic and the variation of the photocurrent with time have been investigated. At low operating voltage the I-V characteristic is ohmic while at high bias voltage an exponential distribution of trap centers gives a good fit to the dark I-V characteristic. The experimental results show a non-exponential growth and decay of photocurrent with rich structure which may indicate a dispersive transport in such disordered amorphous systems. The dispersive transport model has been applied to explain qualitatively the experimental findings of this non-exponential photocurrent behaviour. The experimental data are fitted with a power law function as I _ph (t) t for photocurrent growth and I _ph (t) t ^– for decay where I _ph (t) is photocurrent and and are some constants at a particular bias voltage. The observed slow response speed of the device may be due to slow diffusion of ions as well as the immobilization of charge carriers at deep traps. The present investigation will be helpful to understand the performance of the device and the charge transport mechanism in dye doped solid state polymer electrolyte cell.     

Molecular Switch Controlled by Pulsed Bias Voltages

Recent experiments have shown that the current–voltage characteristics (I–V) of BPDN‐DT (bipyridyl‐dinitro oligophenylene‐ethynylene dithiol) can be switched in a very controlled manner between “on” and “off” traces by applying a pulse in a bias voltage, V_bias. Here, the polaron formation energies are calculated to check a frequently held belief, namely, that the polaron formation can explain the observed bistability. These results are not consistent with such a mechanism. Instead, a conformational reorientation is proposed. The molecule carries an intrinsic dipole moment, which couples to V_bias. Ramping V_bias exerts a force on the dipole that can reorient (“rotate”) the molecule from the ground state (“off”) into a metastable configuration (“on”) and back. By elaborated electronic structure calculations, a specific path for this rotation is identified through the molecule's conformational phase space. It is shown that this path has sufficiently high barriers to inhibit thermal instability but that the molecule can still be switched in the voltage range of the junction stability. The theoretical I–Vs qualitatively reproduce the key experimental observations. A proposal for the experimental verification of the alternative mechanism of conductance switching is presented.     

Growth and characterization of HfO2 high-k gate dielectric films by laser molecular beam epitaxy (LMBE)

The HfO₂ gate dielectric films were fabricated by the laser molecular beam epitaxy (LMBE) technique. High-resolution transmission electron microscopy (HRTEM) observation showed that under optimized condition, there is no detectable SiO₂ interfacial layer in the as-deposited film and a SiO₂ interfacial layer of about 0.4 nm was formed at the Si interface due to the post deposition annealing. Capacitance–voltage (C–V) measurement of the film revealed that the equivalent oxide thickness was about 1.3 nm. Such a film showed very low leakage current density of 1.5 × 10⁻² A cm⁻² at 1 V gate bias from the current–voltage (I–V) analysis. The conduction mechanisms as a function of temperature T and electric field E were also systematically studied.     

A new composition of ceramic varistor: SnO2 doped with (Co,Nb, Al)

A new ceramic voltage sensor based on SnO₂ doped with Co, Nb and Al has been successfully synthesized by ceramic route. The ceramic compact exhibited excellent non-linear current-voltage (I-V) characteristics withα ≈ 24 andE _1mA ≈ 700 V/mm. NCL Communication no. 6345     

Cobalt selenide thin film: photovoltaic and impedance spectral studies by simple chemical grown technique

A thin film of cobalt selenide is deposited on the fluorescence tin oxide-coated glass surface material using a simple chemical growth technique. In this article, we report on the study of photoelectrochemical characteristics (PEC), including current–voltage, capacitance–voltage characteristics, photovoltaic power output, and spectral response in dark and light conditions. For the above parameter study, we prepared using cobalt selenide and carbon electrode (using polysulfide as electrolyte), the battery configuration is expressed as n-CoSe/NaOH (1 M)?+?Na₂S (1 M)?+?S (1 M)/C (graphite). The performance of the cobalt selenide thin film material the resulted values of respective series (R_S) and shunt (R_Sh) resistance 2.280 kΩ and 1.224 Ω, respectively. The efficiency and fill factor of these PEC cells were found to be 0.899 and 28.72%. The junction ideality value are found to be (n_D) is 0.69 in the dark and 2.72 in the light (n_L). The M–S plots are constructed using C^?2 against applied bias voltage (with respect to SCE) for CoSe PEC cell. The positive slope of the M–S plot confirms n-type conductivity of the CoSe films. The carrier density values of the samples obtained from the M–S plots varied from 3.48?×?10¹⁴ cm^?3.

     

Resistive hysteresis in BiFeO3 thin films

Capacitor-like Au/BiFeO₃/SrRuO₃ thin film with (1 1 1) orientation was grown on the SrTiO₃ (1 1 1) substrate by radio frequency magnetic sputtering. It shows a resistive switching behavior, where a stable hysteresis in current–voltage curve was well developed by applying an optimum voltage at room temperature, and it reached the saturation at a bias voltage of 8 V. The Child's law in V_max → 0 direction and the interface-limited Fowler–Nordheim tunneling in 0 → V_max direction, together with the polarization reversal in the BiFeO₃ barrier, are shown to involve in the observed resistive hysteresis.     

The influence of thermally activated flux creep on the ac response of a hard superconductor

A theoretical and experimental study is presented of the influence of thermally activated flux creep on the ac response of a type II superconductor in the mixed state. The theory describes the ac response of a cylindrical superconductor in the mixed state in an axial dc magnetic field and a superposed parallel ac field of low amplitude and low frequency. Thermally activated flux creep gives rise to flux motion at the peak and the valley of the sinusoidal ac applied field and a frequency-independent phase shift of the voltage induced in a pickup coil wound about the sample. The instantaneous voltage at the peak or valley of the ac applied field is related to the critical-current density J _c and the pinning-energy barrier normalized by the temperature U/kT. The ac loss voltage and the voltage waveform were measured for a cold-worked NbZr sample. For temperatures T below 4.2 K, the measured values of kT/U are nearly proportional to the temperature. Both J _c and U were observed to depend on magnetic field history.Research sponsored by the Division of Materials Science, U.S. Department of Energy, under contract W-7405-eng-26 with the Union Carbide Corporation.     

Oxidation of sputtered Zr thin film on Si substrate

Oxidation of sputtered Zr thin film on Si substrate has been investigated by varying oxidation times (5–60 min) at 500 °C. Fourier transform infrared spectroscopy indicated the existence of ZrO₂ by showing spectra of Zr–O. Vibration mode of Si–O and Zr–O–Si are also detected for all samples oxidized at different duration. This suggested the existence of SiO _x and Zr _x Si _y O _z compounds and they might be located at interfacial layers (ILs) between ZrO₂ and Si. Cross-sectional image of high resolution transmission electron microscopy taken from 60-min oxidized sample showed that both ZrO₂ and IL thickness is ~3.5 nm. Time-of-flight secondary-ion-mass spectroscopy suggested that Zr _x Si _y O _z may be formed after oxidized for 15 min. The proposed IL is consisted of a mixture of Zr _x Si _y O _z and SiO _x . A physical model has been established to explain the observation. Electrical characterization shows that capacitance–voltage curves have small hysteresis and their flatband voltages are shifted to a negative bias. Effective dielectric constant values of the investigated oxides are in the range of 4.22–5.29. Leakage current density–breakdown voltage characteristic shows that 5-min oxidized sample has the lowest dielectric breakdown voltage if compared with the other samples.     

Power factor definition in single phase system with arbitrary waveform according to similarity

Abstract

A new definition of power factor, which is suitable for an arbitrary waveform of voltage and current in a single‐phase system, is presented according to similarity between voltage and current waveforms. The similarity is described in infinite dimensions real vector space, and the power factor is defined as the multiplication of rootmean‐ square (RMS) value factor λ _RMS and phase factor λ_?. The new definition is compatible with IEEE Trial‐Use Standard 1459–2000, and can be a useful reference for power factor measurement, power factor correction and power compensation.     

Test results and analyses of conductor short samples for China first PF conductor

The first China PF conductor sample (CNPF1) which was made of one single cable section with hairpin configuration and without bottom joint was fabricated with Chinese NbTi strands and assembled at ENEA and CEA according to the requirements of the SULTAN test facility. The sample was equipped with temperature sensors and voltage taps at CEA according to the test program. The test program included DC performance, cyclic loading, AC loss, and MQE test. The sample exhibited a good performance which fit well with the requirement in the procurement arrangement (PA). But most of the current sharing temperature (T_cs) tests showed a suddenly voltage take-off or fast voltage transition with take-off electric field below the threshold of 10 μV/m. The temperature could be considered as quench temperature (T_q) but not exactly T_cs. At 35 kA and background field of 3.5 T, the temperature T_q was 6.94 K. Even after 2000 cycles at the condition of 6.5 T and 19 kA, the T_q remained unchanged.     

Achieving Fast Charge Separation and Low Nonradiative Recombination Loss by Rational Fluorination for High‐Efficiency Polymer Solar Cells

Four low‐cost copolymer donors of poly(thiophene‐quinoxaline) (PTQ) derivatives are demonstrated with different fluorine substitution forms to investigate the effect of fluorination forms on charge separation and voltage loss (V_loss) of the polymer solar cells (PSCs) with the PTQ derivatives as donor and a A–DA'D–A‐structured molecule Y6 as acceptor. The four PTQ derivatives are PTQ7 without fluorination, PTQ8 with bifluorine substituents on its thiophene D‐unit, PTQ9, and PTQ10 with monofluorine and bifluorine substituents on their quinoxaline A‐unit respectively. The PTQ8‐ based PSC demonstrates a low power conversion efficiency (PCE) of 0.90% due to the mismatch in the highest occupied molecular orbital (HOMO) energy levels alignment between the donor and acceptor. In contrast, the devices based on PTQ9 and PTQ10 show enhanced charge‐separation behavior and gradually reduced V_loss, due to the gradually reduced nonradiative recombination loss in comparison with the PTQ7‐based device. As a result, the PTQ10‐based PSC demonstrates an impressive PCE of 16.21% with high open‐circuit voltage and large short‐circuit current density simultaneously, and its V_loss is reduced to 0.549 V. The results indicate that rational fluorination of the polymer donors is a feasible method to achieve fast charge separation and low V_loss simultaneously in the PSCs.     

Effects of high temperature electron irradiation on trench-IGBT

The degradation of the electrical properties of IGBTs (Insulated-Gate Bipolar Transistors) by 2-MeV electron irradiation at high-temperatures was studied. The irradiation temperatures were 25, 100, 200 and 300^∘C, and the fluence was fixed at 10¹⁵ e/cm². For most experimental conditions, the threshold voltage (V_TH) is observed to recover partially during 100^∘C and the saturation voltage (V_CEsat) increase is most pronounced at 100^∘C. It is shown that in this irradiation temperature range, the temperature dependency of the voltage shift due to the radiation-induced interface traps (Δ V_it) and the voltage shift due to the radiation-induced oxide traps (Δ V_ot) are different, which suggests a possible degradation mechanism for these phenomena. It is tentatively suggested that the diffusion of hydrogen released from the gate by the 2-MeV electrons passivates the interface traps during the high temperature irradiation.     

Photoelectrochemical applications of In<Subscript>2</Subscript>Se<Subscript>3</Subscript> thin films by chemical deposition

Indium selenide films have been synthesized by chemical bath deposition method onto stainless steel plate. The configuration of fabricated cell is n-In₂Se₃| NaOH(1 M) + S(1 M) + Na₂S(1 M) |C_(graphite). Characterization of the photoelectrochemical cell was carried out by studying X-ray diffraction, current–voltage and capacitance–voltage characteristics in the dark, barrier height measurements, power output, photoresponse and spectral response. The study shows that the In₂Se₃ thin films are n-type semiconductor. The junction ideality factor was found to be 3.24. The flat band potential and the barrier height were found to be 0.720 V and 0.196 eV, respectively. From the study of power output characteristics, open circuit voltage, short circuit current, fill factor and efficiency were found to be 310 mV, 20 μA, 37.64 and 0.61%, respectively. Photoresponse studies show that the lighted ideality factor is 2.78. Maximum current was observed at 575 nm.     

Electrical-thermal switching effect in high-density polyethylene/graphite nanosheets conducting composites

The nonlinear response in high-density polyethylene/graphite nanosheets conducting composites under increasing applied voltage is investigated. Under sufficient applied constant voltage, the resistance increases initially due to Joule heating effect and then eventually reaches a steady value with a characteristic thermal relaxation time τ _h , which decreases as the applied field increases. The switch value, namely the ratio of the resistance under steady condition to the resistance of sample in linear regime, gradually increases with the increasing applied field. The threshold voltage (V ₀) at which the resistance start to increase with time scales with linear regime resistance (R ₀) of the sample as with the exponent x = 0.78 ± 0.05. All the curves of R/R ₀ vs. V/V ₀ collapse to a similar curve with the function R/R ₀ = 1 + α(V/V ₀) ^θ . The results reveal that the threshold voltage value decreases with increasing graphite nanosheets content in the composites.     

Effect of the frequency and temperature on the complex impedance spectroscopy (C–V and G–V) of p-ZnGa2Se4/n-Si nanostructure heterojunction diode

X-ray diffraction pattern and AFM results confirm the nanostructure of p-ZnGa₂Se₄/n-Si. The unit cell lattice parameters, the crystallite size L, the dislocation density δ, and the main internal strain ε were calculated. The temperature and frequency-dependent electrical characteristics of the Al/p-ZnGa₂Se₄/n-Si/Al heterojunction diode (HJD) have been investigated to determine the interface states which are responsible for the non-ideal behavior of the characteristics of the diode. The capacitance–voltage (C–V), conductance–voltage (G–V), and series resistance–voltage (R _s–V) characteristics of the diode have been analyzed in the frequency range of 5 kHz–1 MHz and temperature range of 303–423 K. The interfaces states of the diode were determined using conductance–voltage technique. The interface state density profile for the diode was obtained as a function of temperature and frequency. The values of the built-in potential V _bi, the doping concentration N _d and the barrier height φ _b(C–V) of the diode were calculated at different temperatures and frequencies. Our experimental results revealed that both the series resistance and interface state density values must be taken into account in studying the impedance spectroscopy of HJD to stand up their performance for electronic applications characteristics.     

Solution-Processed Organic Solar Cells with High Open-Circuit Voltage of 1.3 V and Low Non-Radiative Voltage Loss of 0.16 V

Compared with inorganic or perovskite solar cells, the relatively large non-radiative recombination voltage losses (ΔV_non-rad) in organic solar cells (OSCs) limit the improvement of the open-circuit voltage (V_oc). Herein, OSCs are fabricated by adopting two pairs of D–π–A polymers (PBT1-C/PBT1-C-2Cl and PBDB-T/PBDB-T-2Cl) as electron donors and a wide-bandgap molecule BTA3 as the electron acceptor. In these blends, a charge-transfer state energy (E_CT) as high as 1.70–1.76 eV is achieved, leading to small energetic differences between the singlet excited states and charge-transfer states (ΔE_CT ≈ 0.1 eV). In addition, after introducing chlorine atoms into the π-bridge or the side chain of benzodithiophene (BDT) unit, electroluminescence external quantum efficiencies as high as 1.9 × 10⁻³ and 1.0 × 10⁻³ are realized in OSCs based on PBTI-C-2Cl and PBDB-T-2Cl, respectively. Their corresponding ΔV_non-rad are 0.16 and 0.17 V, which are lower than those of OSCs based on the analog polymers without a chlorine atom (0.21 and 0.24 V for PBT1-C and PBDB-T, respectively), resulting in high V_oc of 1.3 V. The ΔV_non-rad of 0.16 V and V_oc of 1.3 V achieved in PBT1-C-2Cl:BTA3 OSCs are thought to represent the best values for solution-processed OSCs reported in the literature so far.     

Novel Tunnel‐Contact‐Controlled IGZO Thin‐Film Transistors with High Tolerance to Geometrical Variability

Thin insulating layers are used to modulate a depletion region at the source of a thin‐film transistor. Bottom contact, staggered‐electrode indium gallium zinc oxide transistors with a 3 nm Al₂O₃ layer between the semiconductor and Ni source/drain contacts, show behaviors typical of source‐gated transistors (SGTs): low saturation voltage (V_{D_SAT} ≈ 3 V), change in V_{D_SAT} with a gate voltage of only 0.12 V V^?1, and flat saturated output characteristics (small dependence of drain current on drain voltage). The transistors show high tolerance to geometry: the saturated current changes only 0.15× for 2–50 µm channels and 2× for 9‐45 µm source‐gate overlaps. A higher than expected (5×) increase in drain current for a 30 K change in temperature, similar to Schottky‐contact SGTs, underlines a more complex device operation than previously theorized. Optimization for increasing intrinsic gain and reducing temperature effects is discussed. These devices complete the portfolio of contact‐controlled transistors, comprising devices with Schottky contacts, bulk barrier, or heterojunctions, and now, tunneling insulating layers. The findings should also apply to nanowire transistors, leading to new low‐power, robust design approaches as large‐scale fabrication techniques with sub‐nanometer control mature.