Influence of iodine on the electrical properties of magnesium phthalocyanines thin film devices

The influence of iodine on the electrical properties of sandwich structures of magnesium phthalocyanine (Mg Pc) thin films with gold and aluminium electrodes has been investigated. The various electrical properties and different electrical parameters of the iodine-doped Mg Pc thin film devices have been estimated and compared with the values of normal Mg Pc devices from the analysis of the current-voltage characteristics. Generally samples showed an asymmetric conductivity both under forward and reverse bias. From our study we found that iodine doped Mg Pc films showed an enhanced electrical conductivity of nearly ten times that of typical Mg Pc. At low voltages the films showed an ohmic conduction with a hole concentration of P₀ = 6.34 × 10¹⁸ m⁻³ and hole mobility μ = 9.16 × 10⁻⁵ m ² V⁻¹ s⁻¹, whereas at higher voltage levels the conduction is dominated by space charged limited conduction (SCLC) with a discrete trapping level of 1.33 × 10²² m⁻³ at 0.63 eV above the valance band edge. The ratio of the free charges to trapped charges (trapping factor) for the doped samples was found to be 1.07 × 10⁻⁷. Furthermore the reverse conduction mechanisms have also been investigated. From the current limitations in the reverse condition a strong rectifying behaviour was evident which was attributed to Poole-Frankel emission with a field-lowering coefficient of value 2.24 × 10⁻⁵ eV m^1/2 V^−1/2.     

Thin porous anodic alumina films: Interface trap density determination

The electrical properties of thin porous alumina films in the form of MOS structures were studied with dielectric spectroscopy at room temperature. The thickness of the samples was found to be approximately 95 nm with a cross section area of 1.6×10⁻³ cm².C-V andG-V measurements were performed by applying a loop sweep voltage 2.0 V to −5.0 V. Correction to the measurements were performed by considering a series resistanceR _S and leakage currentI _DC. TheC-V results show hysteresis effects due to the presence of positive charges in porous alumina. These charges may be are attributed to the residual electrolyte during the anodization process in the sample preparation. Three distinct regions in theC-V results are observed, namely the inversion, the depletion and the accumulation regions. In the voltage region, where depletion of carriers is observed,C-f andG-f measurements were recorded in the frequency range 1 Hz to 10⁶ Hz. The conductance method was applied for the calculation of the density D_it of carriers, trapped in the interface between insulator and semiconductor, and of the response time τ_it as a function of the applied bias voltage were performed. The values obtained for D_it and τ_it are of the order of 3×10¹² eV⁻¹ cm⁻² and 10⁻³ s, respectively, and they are voltage dependent. Paper presented at the Patras Conference on Solid State Ionics — Transport Properties, Patras, Greece, Sept. 14 – 18, 2004.     

Bacto agar-based gel polymer electrolyte

The biopolymer of a Bacto agar-based gel polymer electrolyte (GPE) was prepared by addition of NaI and I₂ as redox couple. The prepared GPE was characterized using impedance spectroscopy and X-ray diffraction (XRD) in order to determine its electrical and structural properties, respectively. An optimized ionic conductivity of 12.41 × 10⁻⁴ S cm⁻¹ was achieved for the samples containing 1.6 M NaI and 50 μL I₂. Meanwhile, XRD revealed that the addition of NaI and I₂ altered agar properties and formed an amorphous structure. Linear sweep voltammetry showed that the electrochemical stability window of the sample had a working voltage of 2.0 V.     

Structural and electrical properties of pure and H<Subscript>2</Subscript>SO<Subscript>4</Subscript> doped (PVA)<Subscript>0.7</Subscript>(NaI)<Subscript>0.3</Subscript> solid polymer electrolyte

Solid polymer electrolytes (SPE) based on poly-(vinyl alcohol) (PVA)_0.7 and sodium iodide (NaI)_0.3 complexed with sulfuric acid (SA) at different concentrations were prepared using solution casting technique. The structural properties of these electrolyte films were examined by X-ray diffraction (XRD) studies. The XRD data revealed that sulfuric acid disrupt the semi-crystalline nature of (PVA)_0.7(NaI)_0.3 and convert it into an amorphous phase. The proton conductivity and impedance of the electrolyte were studied with changing sulfuric acid concentration from 0 to 5.1 mol/liter (M). The highest conductivity of (PVA)_0.7(NaI)_0.3 matrix at room temperature was 10⁻⁵ S cm⁻¹ and this increased to 10⁻³ S cm⁻¹ with doping by 5.1 M sulfuric acid. The electrical conductivity (σ) and dielectric permittivity (ε′) of the solid polymer electrolyte in frequency range (500 Hz–1 MHz) and temperature range (300–400) K were carried out. The electrolyte with the highest electrical conductivity was used in the fabrication of a sodium battery with the configuration Na/SPE/MnO₂. The fabricated cells give open circuit voltage of 3.34 V and have an internal resistance of 4.5 kΩ.     

Negative space charge and electric field intensity in polymeric insulators at low temperatures

The effect of negative space charge accumulation due to injection of electrons from cathode microprotrusions on the steady-state and transient electric field distributions in polymer dielectrics is discussed. An isolated microprotrusion is modeled by a spherical capacitor in which an electrode of smaller radius is the cathode. The calculations include the fact that the distribution of negative space charge depends on the rate of capture and liberation of electrons by traps, while the activation energy of this process depends on the electric field intensity. An exponential energy distribution is proposed for the traps. It is shown that significant electrical overvoltages can only appear near the cathode microtips immediately after switching on the voltage. In the course of 10⁻⁶–10⁻⁵ s, the coefficient of electrical overvoltage drops to a few units and approaches its steady-state value. The region of significant electrical overvoltage is localized, and is the same order as the dimensions of the microtip. Fiz. Tverd. Tela (St. Petersburg) 40, 1167–1172 (June 1998)     

Impacts of Ti on electrical properties of Ge metal–oxide–semiconductor capacitors with ultrathin high-k LaTiON gate dielectric

Ge Metal–Oxide–Semiconductor (MOS) capacitors with LaON gate dielectric incorporating different Ti contents are fabricated and their electrical properties are measured and compared. It is found that Ti incorporation can increase the dielectric permittivity, and the higher the Ti content, the larger is the permittivity. However, the interfacial and gate-leakage properties become poorer as the Ti content increases. Therefore, optimization of Ti content is important in order to obtain a good trade-off among the electrical properties of the device. For the studied range of the Ti/La₂O₃ ratio, a suitable Ti/La₂O₃ ratio of 14.7% results in a high relative permittivity of 24.6, low interface-state density of 3.1×10¹¹ eV⁻¹ cm⁻², and relatively low gate-leakage current density of 2.0×10⁻³ A cm⁻² at a gate voltage of 1 V.     

Improvement of plasma-sprayed YSZ electrolytes for solid oxide fuel cells by alumina addition

Atmospheric plasma spray is a fast and economical process for deposition of yttria-stabilized zirconia (YSZ) electrolyte for solid oxide fuel cells. YSZ powders have been used to prepare plasma-sprayed thin ceramic films on the metallic substrate employing plasma spray technology at atmospheric pressure. Alumina doping was employed to improve the structural characteristics and electrical properties of YSZ. The effect of alumina addition from 1 to 5 wt.% on the properties of plasma-sprayed YSZ films was investigated. It was found that the gas permeability of the Al-doped YSZ electrolyte layer reached a level of 8.6 × 10⁻⁷ cm⁴ gf⁻¹ s⁻¹, which is a necessary value for the practical operation of solid oxide fuel cells. Alumina doping considerably increased the ionic conductivity of plasma-sprayed YSZ. The open circuit voltage of the alumina-doped YSZ coating was approximately equal to the theoretical value for dense YSZ material.     

Investigation of temperature-dependent electrical properties of p-VOPc/n-si heterojunction under dark conditions

An organic/inorganic heterojunction p-VOPc/n-Si was fabricated and its electrical properties were investigated. Temperature-dependent dark current–voltage (I–V) characteristics of the heterojunction exhibited rectification behaviour with a rectification ratio of 405 at ±1 V and room temperature. The current–voltage characteristics of the cell showed ohmic conduction at low voltages followed by a space charge-limited current (SCLC) conduction dominated by an exponential trap distribution at higher voltages. At room temperature, the series and shunt resistances were found to be approximately 1.4 and 100 kΩ, respectively. Diode ideality factor n was found to be 3.2 at room temperature and dropped to 1.9 at 363 K. Room temperature mobility of vanadyl phthalocyanine (VOPc) was extracted from the I–V characteristics in the SCLC region and was found approximately 15.5 × 10⁻³ cm² V⁻¹ s⁻¹. The effective barrier height, Ф_B, was estimated as 0.77 eV. The effect of temperature, on various heterojunction parameters was recorded under dark conditions and at temperatures ranging from 300 to 363 K.     

Initial operation at liquid-helium temperature of the M =2270 kg Al 5056 gravitational-wave antenna of the Rome group

Summary We report on the cooling at liquid-helium temperature of our 2270 kg 5056 Al bar at CERN. The liquid-helium container had been filled up to 1500 liters ensuring to keep the antenna cold for more than one month. The antenna is equipped with a resonant capacitive transducer operating at constant electrical charge with a FET low-noise amplifier. The transducer is tuned to the antenna within less than I Hz and the two normal-mode frequencies are ν₋=908.160 Hz and ν₊=924.234 Hz with an applied electrical field in the transducer of 10⁶ V/m. The corresponding overall merit factors areQ ₋=5.20·10⁶ andQ ₊=7.25·10⁶. The transducer has been tested up to an electrical field of 6·10⁶ V/m: in this condition we have βQ≈10⁴. The antenna has been in operation for several weeks giving, for the Brownian noise, values in agreement with the calculated values. We report also on the results of tests performed on a DC SQUID, whose input was connected to a commercial capacitor via a transformer with turn ratio of 1000. Supported in part by Japan Society for the Promotion of Science.     

The characteristics of high current amorphous silicon diodes

Amorphous siliconp−n junctions with various doping profiles have been prepared by the glow discharge technique and the effect of the barrier profile on electrical properties investigated. Current densities of up to 40 A cm⁻² with rectification ratios of 10⁴–10⁵ were obtained withn ⁺−ν−p ⁺ structures. The diode quality factor has also been investigated, both in the dark and under illumination.