Homoepitaxial diamond p–n+ junction with low specific on-resistance and ideal built-in potential

We have realized low specific on-resistance and ideal built-in potential simultaneously for a (111)-oriented homoepitaxial diamond p–n⁺ junction. As the p–n⁺ junction, the heavily phosphorus doped n⁺-type layer, which shows variable range hopping conduction, was formed on the (111)-oriented boron doped p-type one. By using this hopping conduction, the resistivity of the n⁺-type layer becomes lower by three orders of magnitude than that of a lightly P-doped layer. Current density–voltage characteristics showed a rectification ratio of 10⁶ at ± 15 V at room temperature. The current density and the specific on-resistance at forward bias voltage of 15 V at room temperature are over 100 A/cm² and 8 × 10^− 2 Ωcm², respectively. This low specific on-resistance corresponds to the lower resistivity of the n⁺-type layer by three orders of magnitude than that of conventional lightly P-doped n-type layer. The existence of the space-charge layer at the vicinity of the p–n⁺ junction was confirmed from capacitance–voltage (C–V) characteristics. From C⁻²–V characteristics at 200 °C, the built-in potential was estimated as approximately 4.4 eV, which is identical to that of conventional diamond p–n junction.     

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.     

Electrical and light-emitting properties from (111)-oriented homoepitaxial diamond p–i–n junctions

We have succeeded in fabricating a (111)-oriented diamond p–i–n junction with high crystalline quality intrinsic layer and with low series resistance. The series resistance of this diamond p–i–n junction was improved by decreasing the resistivity and specific contact resistance of n-type layer, which is allowed to inject higher current while maintaining lower junction temperature. Current density–voltage characteristics showed a rectification ratio of 10⁶ at ± 15 V at room temperature. A clear ultraviolet emission at around 235 nm due to free exciton recombination was observed at a forward current, while the broad visible light emission from deep levels was significantly suppressed. Moreover, stronger excitonic emission by two orders of magnitude than that of (001)-oriented diamond p–i–n junctions with high series resistance was realized.     

A reaction model for the electrochemical production of p-anisidine

The work examines the possibility of a simple reaction model describing a complex organic electrosynthesis, such as the formation of p-anisidine. The experimental results obey the linear relationships of the model and in consequence the kinetic constants obtained in this way define reaction behaviour. The paper demonstrates how such a model can play a useful role in the design of pilot plant experimentation. Results from a parallel plate cell fit prediction from the model.Nomenclature [X] Concentration of species X (kmol m^–3) - b Slope of Tafel plot (mV^–1) - E Electrode potential (mV) - F Faraday (C g-equiv^–1) - F Faraday based on k-equiv = 10³F (C k-equiv^–1) - i _A Partial current density for the primary reaction (A m^–2) - i _B Partial current density for the consecutive secondary reaction (A m^–2) - i _H Partial current density for the parallel secondary reaction (A m^–2) - i Total current density=i _A+i _B+i _H (A m^–2) - k Reaction rate constant (A m^–2 per kmolm^–3) - k _H Rate constant for the parallel secondary electrode reaction (A m^–2) - k _I Individual mass transfer coefficient (m s^–1) - N Flux (kmol m^–2 s^–1) - r Reaction rate (kmol m^–2 s^–1) Sufixes A Appertaining to primary electrode reaction or species A - B Appertaining to consecutive secondary electrode reaction or species B - b In the bulk of the electrolyte - H Parallel secondary electrode reaction - s Near the electrode surface     

Thermally stable solar-blind diamond UV photodetector

Thermally stable, deep-ultraviolet (DUV) photodetectors are developed by fabricating a semi-transparent tungsten carbide (WC) or hafnium nitride (HfN) Schottky contact and an annealed Ti/WC Ohmic contact on a boron-doped homoepitaxial p-type diamond layer. Thermal annealing at 500 °C improves the rectifying current–voltage characteristics of the photodiode, resulting in a dramatic enhancement (by a factor of 10³) of DUV responsivity at 220 nm. The discrimination ratio between DUV and visible light is measured to be as large as 10⁶ at a reverse bias voltage as small as 2 V, and it remains almost constant after annealing at 500 °C for 5 h. The short-circuit photocurrent of the HfN Schottky photodiode gradually decreases as the annealing temperature increases, which is well explained by the dependence of the depletion layer width beneath the contact interface on the annealing temperature. In contrast, the short-circuit photocurrent of the WC photodiode is rapidly reduced as the temperature increases. The B doping is found to affect the time response property and reducing the B concentration significantly reduces the response time. Metal carbide and nitride contacts for diamond are thus useful for developing a thermally stable diamond UV photodetector.     

Electron emission from CVD diamond p-i-n junctions with negative electron affinity during room temperature operation

We successfully observed electron emission from hydrogenated diamond p-i-n junction diodes with negative electron affinity during room temperature operation. The emissions started when the applied bias voltage produced flat-band conditions, where the capacitance-voltage characteristics showed carrier injection in the i-layer. In this low current injection region, the electron emission efficiency (η) of the p-i-n junction diodes (p is top layer) was about 5 × 10^− 5, while that of the n-i-p diodes (n is top layer) was about 10^− 8. With increasing diode current, both diodes showed an increase in η and a nonlinear increase in emission current. In the high current injection region with high diode current of 5-50 mA, both diodes had an emission current of almost 10 μA, where η of a p-i-n junction diode was 0.18%, while that of a n-i-p junction diode was 0.02%.Note that η, which corresponds to the electron emission mechanism, depended on the diode current level.     

Anodic substitutions in emulsions under phase transfer catalysis conditions. I. Cyanation of dimethoxybenzenes

An emulsion electrolysis technique in the two-phase system water-dichloromethane containing NaCN and a phase transfer agent (PTA) has been examined with 1,2- and 1,3-dimethoxybenzenes as a function of various parameters (nature of Q⁺, X^–, anodic potential, cyanide ion concentration in the organic phase, preparative current potential curves). The anodic cyanation results indicate that the anode wetting phenomena, the extraction of cyanide ion and the competitive oxidation of X^– are the determining factors. It is shown that the best criterion for a successful anodic cyanation is to operate under conditions of maximum coverage of the anode by the organic layer. Among all the PTA studied (cetyltrimethylammonium bromide,nBu4N⁺HSO ₄ ^– ,nBuP⁺₃Br^–, benzethonium chloride and A 336), A 336, a very hydrophobic PTA, affords the best chemical (81%) and current (77%) yields with 1,2,-dimethoxybenzene.     

The influence of mass transport on the deposit morphology and the current efficiency in pulse plating of copper

The morphology of copper deposits formed by pulse plating from an acid sulphate electrolyte is investigated. The steady and non-steady state conditions of mass transport are controlled by use of a rotating hemispherical electrode. Below the limiting pulse current density (i _pl), granular deposits are observed. Abovei _pl, regardless of the individual values of the pulse parameters, dendritic deposits are formed. Measured current efficiencies are compared with a theoretical model, which predicts a rapid decrease of the efficiency with the increasing ofi _p/i _pl fori _p/i _pl greater than one, wherei _p is the applied pulse current density. For a given set of pulse parameters, the measured current efficiency increases with the deposit thickness due to the increase of the effective surface area. This effect is particularly important for dendritic deposits.Nomenclature A apparent (effective) surface area (cm²) - A ₀ geometrical surface area (cm²) - D diffusion coefficient (cm²s^–1) - i current density (A cm^–2) - i _l limiting current density (A cm^–2) - i _p pulse current density (A cm^–2) - i _pl pulse limiting current density (A cm^–2) - i _m average current density in pulse plating (A cm^–2) - N _p dimensionless numberN _p=i _p/i _pl - N _m dimensionless numberN _m=i _m/i _l - t _p pulse time (s) - t_p relaxation time (s) - duty cycle, =t _p/(t _p+t_p) - (steady state) diffusion layer thickness (cm) - _p pulsating diffusion layer thickness (cm) - current efficiency - kinematic viscosity (cm²s^–1) - rotation rate (rad s^–1)     

Highly oriented growth of n-type ZnO films on p-type single crystalline diamond films and fabrication of high-quality transparent ZnO/diamond heterojunction

We present the results on the fabrication and characterization of high-quality transparent heterojunction between n-type ZnO film and p-type diamond single crystalline film on the substrate of diamond bulk single crystal. The results indicated that the current density of the fabricated p-n junction reaches 110 A/m² when the forward bias voltage is 2.5 V, and the turn-on voltage value is about 0.75 V and agreement with the expected value. Moreover, a good rectification characteristic and transparent in the visible light range was obtained in the device.     

Decomposition of NO on Na+-modified MgO evidenced by ESR and temperature programmed desorption (TPD)

The decomposition of NO to N₂O is accompanied by the formation of O^– over a Na⁺-modified MgO surface at moderated temperatures. The importance of the interaction of (Na⁺) _n (n2) clusters and MgO surface is highlighted.     

EPR study of hydrogen-related defects in boron-doped p-type CVD homoepitaxial diamond films

Boron-doped p-type single crystalline chemical vapor deposition (CVD) homoepitaxial diamond films were investigated by electron paramagnetic resonance (EPR). Carbon dangling bond defects, which were accompanied by a nearby hydrogen atom, were observed in boron-doped p-type CVD diamond films on a IIa substrate similar to those observed in undoped diamond. This result suggested that the energy level position of the defects is located below the Fermi energy of boron-doped diamond, at around 0.3 eV above the valence-band top. The reason why the Fermi energy could be changed by the incorporation of boron atoms at low density (10¹⁶–10¹⁷/cm³) in the film in spite of the existence of the large defect density of EPR centers (10¹⁸/cm³) is thought to be that the singly occupied electron states of defects are located near the band edge. As for the thermal annealing effect of the defects, it was revealed that the concentration of the defects and the mobility of the p-type film did not change after annealing up to 1200 °C which is much higher than the temperature of boron–hydrogen pair dissociation.     

Cathodic reduction of hypochlorite during reduction of dilute sodium chloride solution

Sodium chloride solutions of concentration 15 and 30 g dm^–3 were electrolysed in a flow-through electrolyser with a titanium/TiO)₂/RuO₂ anode at current densities 1059–4237 A m^–2. The current yield for the reduction of hypochlorite on a stainless steel cathode was found to be 13–32% at 7 g dm^–3 NaClO, in agreement with that calculated on the basis of the Stephan-Vogt theory. Migration of ions was taken into account, the diameter of hydrogen bubbles was set equal to 0.04 mm and the coverage of the electrode with the bubbles was estimated as = 0.897. The results of calculations show that the reduction rate of hypochlorite at low NaCl concentrations is lowered by migration. Literature data for the reduction of hypochlorite are in accord with the current yield calculated on the basis of the Stephan-Vogt theory using = 0.787 and = 0.949.List of symbols C _i ^o concentration of species i in the bulk (mol m^–3) - C _i ^s concentration of species i at the cathode surface (mol m^–3) - d _B bubble diameter (m) - D _e equivalent diameter (characteristic dimension) (m) - D _i diffusion coefficient of species i (m² s^–1) - f _G gas evolution efficiency - F Faraday constant (96 487 C mol^–1) - j total current density (Am^–2) - j _B current density for gas evolution (Am^–2) - j _{c, lim} limiting current density for cathodic reduction of ClO^– (A m^–2) - j _{c, r} critical current density (A m^–2) - L length of electrode (m) - M migration correction factor - n _B number of electrons exchanged in gas evolution - n _ClO ^– number of electrons exchanged in reduction of ClO^– - N _i flux of species i (mol m^–2 s^–1) - Q charge passed (C) - P _t total gas pressure (Pa) - Re Reynolds number (Equation 14) - Re _B Reynolds number (Equation 17) - Sc Schmidt number (Equation 13) - Sh Sherwood number (Equation 12) - Sh _B Sherwood number (Equation 15) - T absolute temperature (K) - u _i mobility of ion i (m² s^–1 V^–1) - _B fictitions linear velocity of gas formation (ms^–1) - _el rate of electrolyte flow (ms^–1) - V volume of the electrolyte in the system (m³) - V _{H 2} content of hydrogen in gas phase (%) - V _{O 2} content of oxygen in gas phase (%) - y _i current yield (differential) for production of species i (%) - y _r current yield (differential) for reduction of ClO^– and ClO ₃ ^– (%) - Y _ClO–,r current yield (differential) for reduction of CIO^– (%) - Y _i integral current yield for production of species i (%) - z _i charge number of ion i Greek symbols thickness of Nernst diffusion layer (m) - _c thickness of convective diffusion layer (m) - _B thickness of diffusion layer controlled by gas evolution (m) - dynamic viscosity (m² s^–1) - time (s) - coverage of electrode surface with gas bubbles - Galvani potential (V) - correction function (Equation 11)     

Kinetics and mechanism for the hydrothermal decomposition of sodium amalgam promoted on graphite electrodes containing iron

The kinetics for the hydrothermal decomposition of sodium amalgam was studied in the presence of water and caustic soda on graphite electrodes containing iron.Regression analysis of over 1000 data points in a linear regression analysis yielded the following rate expression, explaining 89% of the variance in the data, leaving 11% of the variance unexplained: r=–d(Na)/dt=187.8 (T)^–2/3 exp (– 196.9/RT) (Na)^3/4 (NaOH)^–1/5.The decomposition rate of sodium amalgam is strongly limited by the rate of diffusion of sodium metal atoms in the mercury, and also the activity of water at the active cathodic sites on the catalyst. The activation energy for charge transfer for this process is low at 196.9 cal mol^–1 or 8.5 mV.The range of variables studied was: temperature –25, 50 and 85° C; caustic concentration –10, 30 and 50 wt.%; amalgam concentration –0.1,0.2 and 0.3 mol.%, and finally with iron concentrations in the graphite matrix of – 215.9, 929.5 and 6180 ppm.List of symbols R 1.987 cal (K mol)^–1 = ideal gas law constant - ¯R M-M distance between nearest neighbours in the crystal lattice of the electrode used to calculate the Madelung constant - r i/nF = –d(Na)/dt = reaction rate giving loss of amalgam in mol min^–1 - T (273 + ° C) = absolute temperature (K) - (Na) C _Na = moll^–1 = concentration of sodium in mercury - (NaOH) C _NaOH = moll^–1 = concentration of sodium hydroxide in water solution - Z⁺, Z^– charges on cation and anion, respectively - (M) active centre on the iron promoter catalyst - i total net current density - i ₊ anode partial current density - i _– cathode partial current density - i ₀ exchange current density, ati ₊ =i _– =i ₀, where 0, and the mutually compensating anodic and cathodic current densities are present at the equilibrium potential - overpotential on the electrode,E-E ⁰ - A Arrhenius coefficient, constant - diffusion coefficient of sodium metal in mercury in cm² min^–1 - ¯K rate constant, temperature and activation energy dependent - k rate constant, independent of temperature and activation energy - a _Na (Na) =C _Na = activity of sodium in mercury and to a good approximation equal to its concentration - a _w activity of water in presence of caustic - x distance normal to the catalyst surface (cm) - dx change in distance normal to the catalyst surface - t time at which sample is collected and reaction is quenched - t₀ initial time zero - a, b the order of the reaction, or the exponential power to which the concentration is raised, as opposed to the molecularity of the reaction, or the molecules/collision. The order is empirical and the molecularity is theoretical - Y ln(- d [Na]/dt) = lnk +nlnTE _a/RT +aln(Na) +bln(NaOH), the linear least squares curve fitting program equation - B _0,1,2,3,4 coefficients for the linear least squares curve fitting program - x _i sample measurementi - d x _i-¯X = deviation from the average - standard deviation, d²/¯n - ² variance, or the mean squared deviation from the mean, d ²/¯n - ¯X arithmetic mean,x ₁ +x ₂ + ... x_n/¯n - ¯n total number of measurements.     

AFM and XPS studies of a homoepitaxial diamond (001) surface nitrided using 500-eV N2+ ion beam

A homoepitaxially grown p-type diamond (001) surface was nitrided by irradiation with a 500-eV N₂⁺ ion beam. X-Ray photoelectron spectra (XPS) were taken in situ during the nitridation. The C1s and N1s XPS spectra were divided into three (A, ∼284.7; B, ∼285.6; and C, ∼287.3 eV) and four (D, ∼398.4; E, ∼399.5; F, ∼401.0; and G, ∼403.3 eV) components, respectively. The A component of the C1s core level originated from the diamond substrate lying under the nitrogen penetration zone. The B and C components came from the nitrogen-diluted layer and from the carbon nitrides, respectively. The composition ratio of nitrogen/carbon in the C phase, N_D+F/C_C, was 0.71. The N_all/C_B+C ratio was 0.25. The morphology of the surface was also measured in air by atomic force microscope (AFM). It was found that grain-like material covered the surface after nitridation. A typical grain size was approximately 50 nm in diameter with a height of 5 nm. However, the grains themselves were not carbon nitrides. The crystallinity of the nitride was investigated using reflection high-energy electron diffraction (RHEED), but the formation of β-C₃N₄ could not be confirmed from the RHEED patterns, due to overlapping with the twin structures of diamond.     

Mass transfer and structure of asbestos and non-asbestos diaphragms for chlorine and caustic production

Models and equations describing aspects of diaphragm performance are discussed in view of recent experiences with non-asbestos diaphragms. Excellent control of wettability and, therefore, of the amount of gases inside the diaphragm, together with chemical resistance to the environment during electrolysis, was found to be an essential prerequisite to performances of non-asbestos diaphragms that are comparable to those of asbestos diaphragms. Equations, derived and supported by experimental evidence from previous work, are shown to describe and predict hydrodynamic permeability and ohmic voltage drop of diaphragms, even in cases where the amount of gases inside the diaphragm slowly increases during electrolysis. Current efficiency is observed to be only dependent to a slight extent on the effective electrolyte void fraction inside the diaphragm. Major effects that determine current efficiency at 2 kA m^–2 and 120 gl^–1 caustic are shown to be diaphragm thickness, pore diameter distribution and the number of interconnections between pores inside the diaphragm. A discussion on design of the structure of non-asbestos diaphragms is presented.Nomenclature B permeability coefficient (m²) - c _i,x concentration of ionic species i at position x (mol m^–3) - c _k concentration of hydroxyl ions in catholyte (mol m^–3) - CE current efficiency - d thickness of diaphragm (m) - thickness of layer (m) - D _i ionic diffusion coefficient of species i (m²s^–1) - D _e dispersion coefficient (m²s^–1) - electrolyte void fraction - E potential inside diaphragm (V) - F Faraday constant, 96487 (C mol^–1 of electrons) - F _j,i flux of ionic species i in the stagnant electrolyte inside small pores of layer j - H hydrostatic head (N m^–2) - i flux of current =j/F (mol m^–2s^–1) - j current density (A m^–2) - k _i,l constant representing diffusion in diaphragm (m²s^–1) - k ₂ constant representing migration in diaphragm (m^–1) - v _p hydraulic pore radius according to [15] (m) - N number of layers - N _j,i flux of ionic species i in layer j (mol m^–2s^–1) - P hydrodynamic permeability (m³ N^–1s^–1) - R gas constant, 8.3143 (J mol^–1 K^–1) - density of liquid (kg m^–3) - R ₀ electric resistivity of electrolyte (ohm m) - R _d electric resistivity of porous structure filled with electrolyte (ohm m) - R _m resistance of the diaphragm (ohm m²) - R _a resistance of anolyte layer (ohm m²) - R _e resistance of electrodes (ohm m²) - s specific surface of porous structure (m^–1) - s ₀ standard specific surface of solids in porous structure (m^–1) - tortuosity defined according toR _d/R ₀=/ - T absolute temperature (K) - u superficial liquid velocity (m s^–1) - U cell voltage (V) - dynamic viscosity (N s m^–2) - v kinematic viscosity (m²s^–1) - x diaphragm dimensional coordinate (m) - y radial coordinate inside pores (m) Paper presented at the meeting on Materials Problems and Material Sciences in Electrochemical Engineering Practice organised by the Working Party on Electrochemical Engineering of the European Federation of Chemical Engineers held at Maastricht, The Netherlands, September 17th and 18th 1987.     

Preparation of solid polymer electrolyte composites: investigation of the ion-exchange process

The rate of ion-exchange between an aqueous solution of platinum tetramine and a Nafion^® 117 membrane in H⁺ form is studied. Experimental data are collected using extended X-ray absorption fine structure (EXAFS) spectroscopy in dispersive mode. Results are obtained for various platinum tetramine concentrations in the solution and different hydrodynamic regimes at the membrane-solution interface. A shift from a layer diffusion controlled rate (L) to a membrane diffusion controlled rate (M) is observed when the salt concentration and the stirring of the solution are increased. Time dependent fractional concentration in platinum tetramine inside the membrane are computed for the two limiting cases of diffusion (L and M). Good agreement is found between experimental and simulated data. The role of the rate of ion-exchange on the electrochemical performances of electrode-membrane-electrode composites for water electrolysis applications is discussed.List of symbols A surface of the membrane contacting the solution (1.0 cm²) - A _Pt geometrical area of the platinum RDE (cm²) - C _i concentration of species i in the bulk solution (mol cm^–3) - C _i ^/* concentration of species i in the membrane (mol cm^–3) - C ^– sulfonate concentration in the membrane (mol cm^–3) - C ₀ concentration at the membrane-solution interface (mol cm^–3) - D _i diffusion coefficient of species i in the solution (cm² s^–1) - D _i ^/* diffusion coefficient of species i in the membrane (cm² s^–1) - F Faraday (96 500 C mol^–1) - I _L limiting current of diffusion (A) - K equilibrium constant = at equilibrium = 48 (298 K) - l diffusion layer thickness (cm) - L diameter of the cell (1.2cm) - n number of electron exchanged (2) during the electrooxidation of [Pt(NH₃)₄]²⁺ - N _i fractional concentration of species i in the membrane = z _i C _i ^*/C ^– - Re Reynolds number defined as l/ - Sc Schmidt number defined as /D - t _1/2 time at which 50% of the ion-exchange is achieved - velocity of the solution (cm s^–1) - V volume of the membrane (0.01 cm³) - z _i charge beared by species i - kinematic viscosity of the solution (0.0114 cm² s^–1) assumed to be equal to that of pure water at 298 K - membrane thickness (cm) - rotation speed of the RDE (rad s^–1)     

Investigations in platinum metal group electrochemistry: II The Pd(II)-Pd° reduction

The Norbide boron carbide electrode has been satisfactorily applied to polarographic studies of Pd(II)–Pd° and some other systems involving deposition of metal. By its means the following thermodynamic and kinetic data have been established: standard oxidation-reduction potentials, Pd²⁺–Pd°, 0.91 V; Ag⁺–Ag°, 0.805 V; stability constants, PdCl ₄ ^2– , log ₄, 9·38; logK ₄, 1·44; Pd(SO₄) ₂ ^2– , log ₂, 3·16; activation energies, Pd²⁺–Pd°:Q _D, 18·6; Q°, 188 kJ mole^–1. Analytical applications have been briefly examined.List of symbols A Area of the working electrode - (A°) Apparent frequency factor of the Arrhenius relationship - n Nominally the product of the transfer coefficient, , and the number of electrons,n, involved in an electrochemical process. In practice it is the value obtained from the slopeRT/anF of the lineE v. ln(i ₁–i)/i orv. ln(i ₁–i) - _j Product of dissociation constants of successive complexes:K ₁×K ₂×...×K _j - C ₀ Bulk concentration in the aqueous phase of species undergoing electrochemical reduction or oxidation - D ₀ Diffusivity of that species in the aqueous phase immediately adjacent to the electrode surface - Thickness of a diffusion layer - E _1/2 Half-wave potential, at whichi=i ₁/2 in a polarographic wave of the formE=E _1/2+RT/anF ln(i ₁–i)/i - E _mid Potential at whichi=i ₁/2 in a wave of the formE=E _mid+RT/anF ln(i ₁–i)/i - E _1/2 Displacement of half-wave potential caused by complexing of reducing species - _1/2 Overpotential at the half-wave potentialE _1/2 - _mid Overpotential atE _mid - f Activity coefficient, e.g.f _Pd ^2+(x=0) the activity coefficient of Pd²⁺ species in the aqueous phase at the electrode surface - i ₁ Limiting current - i Current at any stage of the electro-chemical processes governed byE v. ln(i ₁–i)/i relationships - j Number of complexing ligands associated with a cation—e.g. for PdCl ₃ ^– =3 - Q Arrhenius activation energy of the electrochemical process of a reduction at a working electrode [8] - Q _D Arrhenius activation energy of the diffusion stage of an electrochmical reduction [8]     

Significance of logarithmic throwing index: a theoretical approach

An expression for the metal distribution ratio in electroplating systems as a function of the primary current density ratioL in the formM=L [W(1–r)/(1+K)] is derived.W,r andK are three dimensionless parameters related to the current efficiency ratio, the concentration polarization and activation polarization during the metal discharge. The function [W(1–r)/1+K] is compared with 1/A, the logarithmic throwing index empirically determined by Chin. The metal distribution ratio calculated by the use of the above formula is compared with the experimentally observed values. The close agreement between the two within an accuracy of 10% proves the validity of the equation derived. The logarithmic throwing power of electroplating systems is thus confirmed on theoretical grounds.Nomenclature A Logarithmic Throwing Index —inverse of the slope of the plot of logM versus logL - b Tafel slope. Slope of the equation =a + b logi - d_n Current efficiency in percent for metal deposition at near cathode - d _f Current efficiency in percent for metal deposition at far cathode - E The overall cell potential - E _n The potential drop in the electrolyte between the anode and near cathode - E _f The potential drop in the electrolyte between the anode and far cathode - e _a Dynamic anode potential - e _n Dynamic potential at the near cathode at a current densityi _n - e _f Dynamic potential at the far cathode at a current densityi _n - f a fraction = - i The average current density (A dm^–2) - i _n The primary current density at the near cathode when there is no polarization(A dm^–2) - i _f The primary current density at the far cathode when there is no polarization(A dm^–2) - i _n The secondary current density at the near cathode (A dm^–2) - i _f The secondary current density at the far cathode (A dm^–2) - i _{H n} The partial cathode current density at the near cathode for parallel cathodic reactions other than metal discharge (A dm^–2) - i _{H f} The partial cathode current density at the far cathode for parallel cathodic reactions other than metal discharge (A dm^–2) - i _{M n} The partial cathode current density for metal discharge at the near cathode - i _{M f} The partial cathode current density for metal discharge at the far cathode - K A dimensionless parameter =b/2.3E _f - l Linear Ratio =l _f/l _n ori _n i _f - l _n Linear distance of the near cathode (cm) - l _f Linear distance of the far cathode (cm) - M Metal distribution ratio - m _n Weight of metal deposited on the near cathode - m _f Weight of metal deposited on the far cathode - R Secondary current distribution ratio=i _n/i_f - r A dimensionless parameter related toK andf and given byf=(1/L) ^r/K - W A dimensionless parameter related current efficiency ratioR ^W–1 =d _n/d_f - Specific resistivity of the electrolyte( cm^–2) - _n The overpotential at the near cathode (V) - _f The overpotential at the far cathode - i ₀ The exchange current density     

Preparation, characterization and activity evaluation of p–n junction photocatalyst p-CaFe2O4/n-ZnO

p–n junction photocatalyst p-CaFe₂O₄/n-ZnO was prepared by ball milling of ZnO in H₂O doped with p-type CaFe₂O₄. The structural and optical properties of the p–n junction photocatalyst p-CaFe₂O₄/n-ZnO were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV–vis diffuse reflection spectrum (DRS) and fluorescence emission spectra. The photocatalytic activity of the photocatalyst was evaluated by photocatalytic degradation of methylene blue (MB). The results showed that the photocatalytic activity of the p-CaFe₂O₄/n-ZnO was higher than that of ZnO. When the amounts of doped p-CaFe₂O₄ were 0.0 wt.% and 1.0 wt.%, the photocatalytic degradation efficiencies were 50.1 and 73.4%, respectively. Effect of ball milling time on the photocatalytic activity of the photocatalyst was also investigated. The mechanisms of influence on the photocatalytic activity were also discussed by the p–n junction principle.     

Electrical properties of thick boron and nitrogen contained CVD diamond films

The acceptor and donor defects of thick (approx. 0.4 mm) free-standing boron and nitrogen containing microwave plasma CVD polycrystalline diamond films were investigated. Charge-based deep level transient spectroscopy (Q-DLTS) was applied to study impurity-induced defects, their density and energy distribution in the energy range of 0.01 eV≤E−E_v≤1.1 eV above the valence band. It was shown, that differential capacitance–voltage, and Hall effect measurements combined with DLTS data can be used to determine the degree of compensation, and the concentration of compensating donors (mostly the positively charged single-substitutional nitrogen (N⁺)) in p-type CVD polycrystalline diamond films. It was found, that incorporated boron atoms induce three levels of electrically active defects. Two of them with concentration (2–3)×10¹⁶ cm⁻³ each have activation energies of 0.36 and 0.25 eV with capture cross-sections of 1.3×10⁻¹³ and 4.5×10⁻¹⁹ cm², respectively. The third type of defect has an activation energy of 0.02 eV, capture cross-section 3×10⁻²⁰ cm² and concentration 10¹⁵ cm⁻³, this shallow trap being a probable general caterer of holes in low-doped films. The total concentration of electrically active uncompensated acceptors in all p-type diamond samples was approximately 2×10¹⁷ cm⁻³ with hole concentration of approximately 1.5×10¹⁴ cm⁻³ and hole mobility in the range of 30–40 cm² V⁻¹ s⁻¹ at room temperature. If assumed that compensating donors are mostly nitrogen, the films contained no less than 3×10¹⁶ cm⁻³ of N⁺.