Electrical characterization of phosphorus-doped n-type homoepitaxial diamond layers

Electrical properties of phosphorus (P)-related donors have been investigated for P-doped homoepitaxial diamond layers grown by microwave plasma CVD. Temperature-dependent current–voltage (I–V), capacitance–voltage (C–V) measurements and frequency-dependent C–V measurements have been carried out with lateral dot-and-plane (with ring-shaped gap) Schottky barrier diodes. N-type Schottky junction properties were obtained. The ideality factor and the rectification ratio of the Schottky junction were obtained to be 1.9 and 1.7×10⁵ at ±10 V and 473 K, respectively. Frequency-dependent measurements on these Schottky barrier diodes have shown that the capacitance is reduced at high frequency, most likely due to the inability of deep centers to maintain an equilibrium ionization state under a high-frequency modulation. C–V measurements deduced that the net donor concentration was 6.2×10¹⁷ cm⁻³ and the corresponding built-in potential was 4.0 eV, when the P concentration was 8.3×10¹⁷ cm⁻³. Phosphorus electrical activity was 0.75 in the P-doped diamond layer. The carrier thermal activation energy (the donor level) was evaluated to be 0.6 eV from the relation between the net donor concentration and the carrier concentration.     

Defect studies and photoelectrical properties of phosphorus doped amorphous carbon films

This paper reports on the successful deposition of n-type phosphorus doped carbon (n-C:P) thin films and fabrication of n-C:P/p-Si cells by pulsed laser deposition (PLD) using graphite target at room temperature. The cell performances have been tested in the dark for the current–voltage (I–V) rectifying curve and I–V working curve under illumination when exposed to AM 1.5 SUN illumination condition (100 mW/cm², 25 °C). The cells fabricated using 7% of phosphorus by weight percentages in the graphite target (Pwt%) show the highest energy conversion efficiency, η=1.14% and fill factor, FF=41%. The quantum efficiency of the cells is observed to improve with Pwt%. The dependence of Pwt% on the optical and physical properties of the deposited films and the photovoltaic characteristic of the n-C:P/p-Si heterojunction cells are discussed.     

Investigation of specific contact resistance of ohmic contacts to B-doped homoepitaxial diamond using transmission line model

In this study, metal (Ti/Pt/Au) contacts to mesa of boron-doped (boron concentration: 10¹⁸ cm⁻³) homoepitaxial diamond were fabricated by metal deposition followed by thermal annealing at 450 °C. Specific contact resistance was determined by characterizing the current–voltage (I–V) relations from transmission line model (TLM) measurement. The specific contact resistances determined from linear TLM corresponding to different lengths of rectangular contacts were in the order of 10⁻⁴ Ω cm². The results suggest that it is possible to reduce the specific contact resistance to 10⁻⁵–10⁻⁶ Ω cm², which would satisfy the operational requirements of diamond electronic devices, provided the dopant concentration in diamond can be increased to 10¹⁹–10²⁰ cm⁻³.     

Synthesis of nitrogen incorporated diamond-like carbon thin films using microwave surface-wave plasma CVD

Nitrogenated diamond-like (DLC:N) carbon thin films have been deposited by microwave surface wave plasma chemical vapor deposition on silicon and quartz substrates, using argon gas, camphor dissolved in ethyl alcohol composition and nitrogen as plasma source. The deposited DLC:N films were characterized for their chemical, optical, structural and electrical properties through X-ray photoelectron spectroscopy, UV/VIS/NIR spectroscopy, Raman spectroscopy, atomic force microscope and current–voltage characteristics. Optical band gap decreased (2.7 to 2.4 eV) with increasing Ar gas flow rate. The photovoltaic measurements of DLC:N / p-Si structure show that the open-circuit voltage (V_oc) of 168.8 mV and a short-circuit current density (J_sc) of 8.4 μA/cm² under light illumination (AM 1.5 100 mW/cm²). The energy conversion efficiency and fill factor were found to be 3.4 × 10^{− 4}% and 0.238 respectively.     

A study of relaxation processes in Li---MnO2 cells

We analyze the decay of voltage V with time t after a current pulse has been applied to a Li---MnO₂ cell. We plot −tdV/dt and t²d²V/dt² and show that we can resolve two distinct processes in the relaxation of the voltage. We show that the faster decay process is associated with diffusion in the electrolyte, both in the separators and in the pores of the cathode. The peak of the larger time constant appears to be associated with the cathode particles themselves. We calculate an upper bound for the diffusion constant of Li in MnO₂ to be 6 × 10⁻¹² cm²s^−1.     

Effect of neutron irradiation on the structural,mechanical, and thermal properties of jute fiber

This article describes the effect of neutron irradiation on jute fiber (Corchorus olitorius). The jute fibers (4.0 tex) were irradiated by fast neutrons with an energy of 4.44 MeV at different fluences ranging from 2 × 10⁹ to 2 × 10¹³ n/cm². An important aspect of neutron irradiation is that the fast neutrons can produce dense ionization at deep levels in the materials. Structural analysis of the raw and irradiated fibers were studied by small‐angle X‐ray scattering (SAXS), X‐ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy. Thermal analysis carried out on the raw and irradiated fibers showed that the thermal stability of the fibers decreased after irradiation. The mechanical properties of the jute fibers were found to decrease after irradiation. The SAXS study showed that the average periodicity transverse to the layer decreased after irradiation, which may have been due to the shrinkage of cellulosic particles constituting the fiber. The residual compressive stress developed in the fiber after irradiation resulted in a decrease in crystallite size as supported by our XRD analysis. Observation with SEM did not indicate any change produced in the surface morphology of the fiber due to irradiation. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Mass transfer enhancement by the counter-electrode gases in a new cell design involving a three-dimensional gauze electrode

Limiting currents and mass transfer coefficients were measured for the electrodeposition of copper from an acidified solution of copper sulphate at an array of closely packed screens stirred by oxygen. The oxygen evolved at a horizontal lead anode placed below the screen array. Variables studied were: oxygen discharge rate, electrolyte concentration and number of screens per array. For a single-screen electrode, oxygen discharge was found to increase the mass transfer coefficient according to the equation logK =a + 0.377 logV. The mass transfer coefficient was found to decrease slightly with increasing number of screens per array, the decrease becoming pronounced when the number of screens per array reached six. A new cell design involving an array of closely packed screens as a working electrode stirred by the counter-electrode gases is described and its merits and disadvantages are pointed out.List of symbols a constant - I limiting current (A) - Z number of electrons involved in the reaction - F the Faraday (96 500 C) - K mass transfer coefficient (cm s^–1) - C concentration of copper sulphate (mol l^–1) - V oxygen discharge rate (cm³cm^–2s^–1)     

The role of mass transfer in the kinetics of anodic dissolution of gas-evolving metallic surfaces

The rate of anodic dissolution of copper in phosphoric acid above the potential where oxygen evolution takes place was studied. Variables investigated were oxygen discharge rate, phosphoric acid concentration and electrode position. The mass transfer coefficient of the anodic dissolution of copper in phosphoric acid was related to the oxygen discharge rate and the physical properties of the solution by the equations for a vertical electrode:k=aV ^0.2(/u)^0.93 for a horizontal electrode:k=aV ^0.21(/u)^0.93 List of symbols k mass transfer coefficient (cm s^–1) - V oxygen discharge rate, (cm³cm^–2min^–1) - a constant - I current consumed in copper dissolution(A cm^–2) - Z number of electrons involved in the reaction - F Faraday's constant - C Solubility of copper phosphate in H₃PO₄,(mol cm^–3) - N rate of copper dissolution, (g-ion cm^–2s^–1) - diffusion layer thickness (cm) - r bubble radius (cm) - g acceleration of gravity (cm s^–2) - ¯V rise velocity of O₂ bubble (cm s^–1) - u viscosity (poise) - density (g cm^–3)     

Enhanced mass transfer at the rotating cylinder electrode: III. Pilot and production plant experience

Enhanced mass transfer at a rotating cylinder electrode, due to the development of surface roughness of a metal deposit, has been studied in a range of commercial and pilot scale reactors known as ECO-CELLS. The data obtained for relatively restricted ranges of process parameters show reasonable agreement with the more definitive data obtained under laboratory conditions. With scale-up factors of approximately six times in terms of the rotating cylinder diameter, enhanced mass transfer factors of up to 30 times are reported (in comparison with hydrodynamically smooth electrodes) due to the development of roughened deposits during the process of metal extraction from aqueous solution.Nomenclature a, b, c constants in Equation 15 - A active area of rotating cylinder (cm²) - C (bulk) concentration of metal (mol cm^–3 or mg dm–3) - c concentration change over reactor (mol cm^–3 or mg dm^–3) - C _IN,C _OUT,C _CELL inlet, outlet and reactor concentrations of metal (mol cm^–3 or mgdm^–3) - d diameter of rotating cylinder (cm) - D diffusion coefficient (cm₂ s_–1) - f _R fractional conversion - F Faraday constant=96 500 A s (mo1^–1) - I current (A) - I _L limiting current (A) - I _o useful current (A) - j _D ^' mass transport factor (=St Sc ^c) - K constant in Equation 27 - K _L mass transport coefficient (cm s^–1) - m slope of Fig. 8 (s^–1) - M molar mass of copper = 63.54 g mol^–1 - n number of elements in the cascade - N volumetric flow rate (cm^{3 –1}) - P Reynolds number exponent for powder formation (Equation 28) - R total cell resistance (Q) - t time (s) - U peripheral velocity of cylinder (cm s^–1) - V _cell cell voltage (V) - V _R,V _T effective cell, reservoir volume (cm³) - W electrolytic power consumption (W) - x velocity index in Equation 27 - z number of electrons - Re Reynolds number=Ud/v - Sc Schmidt number=v/D - St Stanton number=K _L/U - gu kinematic viscosity (cm² s^–1) - cathode current efficiency - rotational speed (revolutions min^–1) - peak to valley roughness (cm)     

Usability of diamond detectors for spectrometric measurements of lost alpha particles

Measurement of energy of the lost alpha particles (‘escaping alpha particles’) from the thermonuclear reaction in the tokamak is important to obtain information on the energetic balance in future thermonuclear reactors which will be used in power plants. A synthetic high purity CVD monocrystalline diamond detector has been tested in aspect of its potential application for spectrometric diagnostic of the lost alphas of which maximum energy from the thermonuclear reaction is equal to 3.5 MeV. Spectrometric properties of the diamond detector (Diamond Detector, Ltd.) of the 50 μm thickness have been performed using alpha particles of defined energies. The energy calibration and the study on the energy resolution have been carried out using a triple alpha particle isotopic source AMR33 (²³⁹Pu + ²⁴¹Am + ²⁴⁴Cm) with the alpha energy peaks at ca. 5.2, 5.5 and 5.8 MeV, the (²¹²Bi + ²¹²Po) isotopic source of energy 6.0 and 8.7 MeV and a van de Graaff accelerator delivering a well defined monoenergetic alpha beam, changed between 0.4 and 2 MeV. A 14 MeV neutron generator has been employed as a source of alpha particles from D–T reaction accompanied by another induced radiation to test the behaviour of the diamond detector under such conditions.     

Computer simulation of high-discharge-rate battery systems

Simulations were carried out for a proposed two-dimensional high-discharge-rate cell under load with an interelectrode gap of the order of 100 m. A finite difference program was written to solve the set of coupled, partial differential equations governing the behaviour of this system. Cell dimensions, cell loads, and kinetic parameters were varied to study the effects on voltage, current and specific energy. Trends in cell performance are noted, and suggestions are made for development of cells to meet specific design criteria. Modelling difficulties are discussed and suggestions are made for improvement.Nomenclature A surface area of unit cell (cm²) - A _k conductivity parameter (cm^{2 –1} mol^–1) - b Tafel slope (V) - c concentration (mol cm^–3) - c ₀ concentration of bulk electrolyte (mol cm^–3) - D diffusivity (cm² s^–1) - D _h lumped diffusion parameter (J s cm^–2 mol^–1) - D _s lumped diffusion coefficient (A cm² mol^–1) - E rest potential of electrode (V) - F Faraday constant (96 500 C mol^–1) - i current density (A cm^–2) - I total current for unit cell (A) - i ₀ exchange current density (A cm^–2) - N flux of charged species (mol cm² s^–1) - R gas constant (8.314 J mol^–1 K^–1) - R _ext resistance external to cell () - t time (s) - T temperature (K) - t ₀ transference number - u mobility (cm² mol J^–1 s^–1) - V volume of an element in the cell (cm³) - V _ext voltage external to cell (V) - z charge on an ion - _c concentration overpotential (V) - _s surface overpotential (V) - conductivity (^–1 cm^–1) - stoichiometric coefficient - electric potential in solution (V)     

Electrochemical performance of Li3V2(PO4)3/C cathode material using a novel carbon source

Polyethylene glycol (PEG, mean molecular weight of 10,000) has been used to prepare a Li₃V₂(PO₄)₃/C cathode material by a simple solid-state reaction. The Raman spectra shows that the coating carbon has a good structure with a low I_D/I_G ratio. The images of SEM and TEM show that the carbon is dispersed between the Li₃V₂(PO₄)₃ particles, which improves the electrical contact between the corresponding particles. The electronic conductivity of Li₃V₂(PO₄)₃/C composite is 7.0 × 10⁻¹ S/cm, increased by seven orders of magnitude compared with the pristine Li₃V₂(PO₄)₃ (2.3 × 10⁻⁸ S/cm). At a low discharge rate of 0.28C, the sample presents a high discharge capacity of 131.2 mAh/g, almost achieving the theoretical capacity (132 mAh/g) for the reversible cycling of two lithium. After 500 cycles, the discharge capacity is 123.9 mAh/g with only 5.6% fading of the initial specific capacity. The Li₃V₂(PO₄)₃/C material also exhibits an excellent rate capability with high discharge capacities of 115.2 mAh/g at 1C and 106.4 mAh/g at 5C.     

Effect of anodically evolved gas bubbles on the rate of cathodic mass transfer in a vertical cylinder cell

Mass transfer coefficients were measured for the deposition of a copper from acidified copper sulphate solution at a vertical cylinder cathode stirred by oxygen evolved at a coaxial vertical cylinder lead anode placed upstream from the cathode and flush with it. The cathodic mass transfer coefficient was increased by a factor of 2.75–6.7 over the natural convection value depending on the rate of oxygen discharge at the lead anode and height of the cathode. The data were correlated by the equation:J=0.66(F_rR_e)^–0.21 An electrochemical reactor built of a series of vertical coaxial annular cells stirred by the counter electrode gases is proposed as offering an efficient way of stirring with no external stirring power consumption.Nomenclature a, b, c constants - C concentration of copper sulphate, mol cm^–3 - d cylinder diameter, cm - D diffusivity, cm² s^–1 - F Faraday's constant - g acceleration due to gravity, cm² s^–1 - h electrode height, cm - i current density at the oxygen generating anode, A cm^–2 - I _L limiting current density, A cm^–2 - K mass transfer coefficient, cm s^–1 - P gas pressure, atm - R gas constant, atm cm³ mol^–1 K^–1 - T temperature, K - u solution viscosity, poise - V oxygen discharge rate as defined by Equation 9, cm³ cm^–2 s^–1 or cm s^–1 - Z number of electrons involved in the reaction - J mass transferJ factor (S _tS_c ^0.66) - S _t Stanton number (K/V) - S _c Schmidt number (v/D) - S _h Sherwood number (Kh/D) - R _e Reynold's number (/Vh/u) - F _r Froude number (V ² /hg) - G_r Grashof number [gh ³/v² (1–)] - density of the solution, g cm^–3 - kinematic viscosity, cm² s^–1 - void fraction of the gas in the liquid-gas dispersion     

Mass transfer behaviour of gas-evolving particulate-bed electrode

Rates of mass transfer for the cathodic reduction of potassium ferricyanide at a particulate bed of graphite supported on a horizontal nickel disc were studied under H₂-evolving conditions. Variables studied were: H₂ discharge rate, particle size and bed height. The rate of mass transfer was found to increase to a maximum in the presence of the bed which was about 4.5 times compared to that of the supporting disc. The rate of mass transfer was found to increase with H₂ discharge rate, particle size and bed height. Polarization was measured for beds of different particle size and it was found that the presence of the bed increased polarization especially at relatively high current densities, the increase in polarization was independent of particle size of the bed. Comparison with an O₂-evolving particulate electrode was made and possible practical applications were pointed out.Symbols K mass transfer coefficient (cm s^–1) - V H₂ discharge rate (cm³cm^–2s^–1) - I current consumed in reducing potassium ferricyanide (A) - A supporting disc area (cm²) - F Faradays constant (96 500 C mol^–1) - C Potassium ferricyanide concentration (mol cm^–3) - Z number of electrons involved in the reaction     

Effect of neutron irradiation on the mechanical properties of graphite fiber-based composites

Polymer and carbon composite materials reinforced with K-1100 ultra-high modulus fibers were subject to testing of their radiation resistance. Mechanical tests have been carried out, prior and after neutron irradiation at a dose of 7.1×10¹⁷ n/cm² (E>0.5 MeV) for organic matrix composite and 7.3×10¹⁷ n/cm² (E>0.5 MeV) for carbon matrix composite, to assess the radiation resistance. Flexural strength, deformation at break, Young’s modulus and dimensional changes were measured. Microstructure of the composites before and after irradiation was analyzed. The results showed that neutron irradiation causes significant changes in mechanical properties of composites with organic and carbon matrix and a slight variation in their dimensions. Stronger effects in mechanical properties changes for composites with carbon matrix were observed.     

The Influence of Gamma Irradiation Dose on the Formation of Radiation Defects in xCu2Se · (1 – x)As2Se3 Glasses

The defects generated under exposure to gamma radiation at a temperature of 77 K in glasses lying along the xCu₂Se · (1 – x)As₂Se₃ quasi-binary join are studied by the electron paramagnetic resonance (EPR) method. The intensity of EPR signals (I) of radiation-induced defects associated with dangling bonds of atoms in the glass network is examined as a function of the gamma irradiation dose (D = 10⁴–1.5 × 10⁵ Gy). Unlike the As₂Se₃ glass, for which the signal intensity increases almost linearly with an increase in the irradiation dose, the curves I(D) for ternary glasses are characterized by saturation dependent on the copper content in the network. The saturation of the dependences I(D) at a high copper content is explained by the formation of regions with an increased Cu content and the enhancement of the electron–phonon interaction, which prevents the stabilization of dangling bonds in the glass network. The concentration of NO₂ paramagnetic molecules formed by nitrogen and oxygen uncontrollable impurities increases linearly with an increase in the irradiation dose.     

A particulate vortex bed cell for electrowinning: operational modes and current efficiency

The process of electrowinning of copper ions from dilute solutions has been used as a model system to assess the performance of a vortex bed cell with a three-dimensional cathode of conducting particles. Experiments were carried out under three conditions: with constant cell voltage, with constant cell current throughout the process and with exponential decrease of the operating current with time in order to underfollow the limiting current. Results from a batch recirculating system indicate that exponential decrease of operating current with time effects an improvement in current efficiency over a wide range of concentration.Nomenclature specific surface area of particles (cm^–1) - C, C _i concentration of Cu²⁺ ions at the momentt, and initial concentration, respectively (M) - d _p particle diameter (cm) - F Faraday number (96 487 A s mol^–1) - i current density (Am^–2) (calculated for the surface area of the particles) - i _av average current density obtained in the constant cell voltage process (Am^–2) - I _L(t),I _L o limiting current at timet, and initial limiting current, respectively (A) - k _L mass transfer coefficient (cm s^–1) - n number of electrons transferred in the process - Q volumetric flow rate (dm³ s^–1) - R universal gas constant (J mol^–1 K^–1) - t time (s) - T temperature (K) - U cell voltage (V) - V volume of electrolyte (cm³) - v _o volume of particles (cm³) - overpotential (V) - _e current efficiency - , _o bed porosity and porosity of the fixed bed, respectively - =V/Q residence time (s) - see Fig. 2     

Radiation Resistance and Mechanical Stability of SiO2–BaO-Based Glass Coatings for Space Solar-Cell Panels

The influence of proton irradiation (energy, 18 MeV; beam current, 300 nA) with doses of 5 × 10¹⁴, 10¹⁵, and 5 × 10¹⁵ cm^–2 on samples of SiO₂–BaO-based glass coatings is investigated. The absorption, photoluminescence, and gamma luminescence spectra of the studied samples and their microhardness are measured. It is found that proton irradiation leads to a twofold increase in the microhardness. An insignificant increase in the optical absorption is revealed in the near-ultraviolet range (200–400 nm). This increase is accompanied by a decrease in the intensity of both light scattering in the wavelength range 400–900 nm and photoluminescence. The intensity of broadband gamma luminescence with a maximum at a wavelength of 500 nm increases with increasing proton irradiation dose. This means that excitonic radiative recombination impedes the formation of structural defects and their associated color centers. The combined effect of proton irradiation and solar electromagnetic radiation (gamma and visible light rays) accompanied by temperature changes in the range 80–470 K can provide an increase in the radiation resistance and mechanical stability of glass coatings used for solar-cell panels and their longer service life even under conditions of increased solar activity.     

A comparative study of the effect of different drag-reducing polymers on electrochemical mass transfer

The effect of Polyox, Separan and CMC drag-reducing polymers on the rate of electrochemical mass transfer was studied using the cathodic reduction of K₃Fe(CN)₆ in neutral media at a rotating cylinder cathode. Reynolds number and polymer concentration were varied over the ranges 764–10470 and 10–200 ppm respectively. Under these conditions it was found that the three polymers reduce the rate of mass transfer by a maximum of 47%, 30%, and 17% for Polyox, Separan and CMC, respectively. Mass transfer data in the three polymer solutions was correlated by the following equations: for Polyox: (St)=0.051(Re)^–0.3 (Sc)^–0.644 (u/u ₀ ^–0.7 for Separan: (St)=0.065(Re)^–0.3 (Sc)^–0.644 (u/u ₀)^–0.7 for CMC: (St)= 0.075(Re)^–0.3 (Sc)^–0.644) (u/u ₀)^–0.5 List of symbols I limiting current density (A cm^–2) - Z number of electrons involved in the reaction - F Faraday's constant - K mass transfer coefficient (cm s^–1) - V linear velocity of the cylinder (cm s^–1) - D diffusion coefficient (cm²s^–1) - v kinematic viscosity (cm²s^–1) - d diameter of the cylinder (cm) - u, u ₀ viscosity of solutions with and without polymer respectively (P) - density (g cm^–3) - c concentration of Fe(CN) ₆ ^3– (mol cm^–3) - (St) Stantonnumber=K/V - (Sc) Schmidt number=v/D - (Re) Reynolds number=Vd/u     

First In Situ Raman Study of Vanadium Oxide Based SO2 Oxidation Supported Molten Salt Catalysts

In situ Raman spectroscopy at temperatures up to 500°C is used for the first time to identify vanadium species on the surface of a vanadium oxide based supported molten salt catalyst during SO₂ oxidation. Vanadia/silica catalysts impregnated with Cs₂SO₄ were exposed to various SO₂/O₂/SO₃ atmospheres and in situ Raman spectra were obtained and compared to Raman spectra of unsupported model V₂O₅–Cs₂SO₄ and V₂O₅–Cs₂S₂O₇ molten salts. The data indicate that (1) the V^V complex V^VO₂(SO₄)₂ ^3– (with characteristic bands at 1034 cm^–1 due to (V=O) and 940 cm^–1 due to sulfate) and Cs₂SO₄ dominate the catalyst surface after calcination; (2) upon admission of SO₃/O₂ the excess sulfate is converted to pyrosulfate and the V^V dimer (V^VO)₂O(SO₄)₄ ^4– (with characteristic bands at 1046 cm^–1 due to (V=O), 830 cm^–1 due to bridging S–O along S–O–V and 770 cm^–1 due to V–O–V) is formed and (3) admission of SO₂ causes reduction of V^V to V^IV (with the (V=O) shifting to 1024 cm^–1) and to V^IV precipitation below 420°C.