Capacitance–voltage profiling of deuterium passivation and diffusion in diamond Schottky diodes

Capacitance–voltage measurements have been performed on deuterated boron-doped natural type IIb diamond. They demonstrate the electrical passivation of the boron acceptors, which was manifested by a persistent decrease in capacitance after deuteration. Bias annealing experiments have been carried out to determine the charge state of the diffusing deuterium. The differences between annealing with or without bias lead to the conclusion that boron–deuterium complexes dissociate at about 750 K and that the released deuterium is positively charged.     

Characterization of capacitance–voltage features of Ni/diamond Schottky diodes on oxidized boron-doped homoepitaxial diamond film

The electrical properties of Ni/diamond Schottky diodes fabricated on oxidized boron-doped homoepitaxial diamond film have been studied in order to investigate the electrical behavior of diamond-based electronic devices. The current–voltage (I–V) characteristics of the Ni–Schottky contacts to the boron-doped homoepitaxial diamond film show excellent rectification properties. The capacitance–voltage (C–V) features of the Ni/diamond Schottky diodes were characterized in the frequency range from 10⁻³ to 2×10⁵ Hz. The C–V measurements indicate that the space charge density (N_I) and built-in potential (V_d) values are approximately 6.0×10¹⁶ cm⁻³ and 1.25 V, respectively, and show weak frequency dependence in the range from 10⁻³ to 10⁴ Hz. Capacitance–frequency measurement at zero bias indicated that the degrading capacitance at high frequency (>10⁴ Hz) is primarily due to the high series resistance of the homoepitaxial diamond film.     

Preparation and effects of post-annealing temperature on the electrical characteristics of Li–N co-doped ZnSnO thin film transistors

In this study, transparent Li–N co-doped ZnSnO (ZTO: (Li, N)) thin film transistors (TFTs) with a staggered bottom-gate structure were fabricated by radio frequency magnetron sputtering at room temperature. Emphasis was placed on investigating the effects of post-annealing temperature on their physical and electrical properties. An appropriate post-annealing temperature contributes not only to achieving good quality thin films, but also to improving the electrical performance of the ZTO: (Li, N) TFTs. The ZTO: (Li, N) TFTs annealed at 675 °C showed the best electrical characteristics with a high saturation mobility of 26.8 cm²V⁻¹s⁻¹, a threshold voltage of 6.0 V and a large on/off current ratio of 4.5×10⁷.     

The effect of TiO2 particle size on the characteristics of Au–Pd/TiO2 catalysts

The nanocrystalline TiO₂ materials with average crystallite sizes of 9 and 15 nm were synthesized by the solvothermal method and employed as the supports for preparation of bimetallic Au/Pd/TiO₂ catalysts. The average size of Au–Pd alloy particles increased slightly from sub-nano (< 1 nm) to 2–3 nm with increasing TiO₂ crystallite size from 9 to 15 nm. The catalyst performances were evaluated in the liquid-phase selective hydrogenation of 1-heptyne under mild reaction conditions (H₂ 1 bar, 30 °C). The exertion of electronic modification of Pd by Au–Pd alloy formation depended on the TiO₂ crystallite size in which it was more pronounced for Au/Pd on the larger TiO₂ (15 nm) than on the smaller one (9 nm), resulting in higher hydrogenation activity and lower selectivity to 1-heptene on the former catalyst.     

Electrical response of microcellular EPDM rubber composites: complex dielectric modulus formalism and current–voltage characteristics

Electrical response of conductive carbon black (Vulcan XC 72)-reinforced microcellular EPDM rubber composites has been studied as a function of variation in blowing agent and filler loading in the frequency range of 10–10⁵ Hz. The data was analyzed by dielectric modulus formalism. The examined system exhibit a strong dependence of dielectric modulus on the applied frequency. A gradual increase of real part of dielectric modulus with frequency is observed for all fillers and blowing agent loadings. The imaginary part of the dielectric modulus exhibited one relaxation peak with frequency at each filler and blowing agent loading. With increase in filler loading the peak shifts toward higher frequency whereas, with blowing agent loading the relaxation peak shifts toward lower frequency. The relationship between real and imaginary part of dielectric modulus shows a semicircular trend followed by a linear increase for all filler and blowing agent loadings. Hence, the presence of non-Debye type of relaxations has been confirmed. The effect of variations in filler and blowing agent loading on current–voltage characteristics has also been investigated. It is observed that with increase in filler and blowing agent loading, the nonlinearity of the curves increases and the point from which this nonlinearity starts decreases to lower voltage values. It is also observed that the electrical current is free from time when the measuring voltage is low. But as the applied voltage increase to 30 and 40 V, the electrical current changes with time.     

Effects of carbothermal prereduction temperature and Co content on mechanical properties of WC–Co cemented carbides

WC–Co cemented carbides were prepared via an in situ synthesis method, including the carbothermal prereduction of WO₃ and Co₂O₃ to remove all oxygen and a subsequent carbonization-vacuum sintering process. The experimental results revealed that as the prereduction temperature increased from 1000 to 1200°C, the grain sizes of WC in WC–6Co and WC–12Co cemented carbides increased from .91 to 1.09 and .97 to 1.19 μm, respectively. Further, the fracture toughness of the sintered WC–6Co and WC–12Co cemented carbides increased from 9.97 to 10.83 and 11.11 to 18.30 MPa m^1/2, respectively. In contrast, the hardness of the WC–6Co and WC–12Co cemented carbides decreased from 1477 to 1368 and 1351 to 1184 HV₃₀, respectively. For a given prereduction temperature, an increase in Co content can improve the fracture toughness while lowering the hardness. In addition, an increase in the prereduction temperature or Co content led to an increase in the grain size of WC, which resulted in a transgranular fracture as the dominant mode.     

The preparation and characteristics of poly(methyl methacrylate–methylacrylate acid)/nano-ZnO composite latex particles

In this work, poly(methyl methacrylate-co-methylacrylate acid)/ZnO (poly(MMA–MAA)/ZnO) composite latex particle was synthesized by three steps The first step was to synthesize poly(MMA–MAA) copolymer latex particles by soapless emulsion polymerization. Following the first step, the second step was to polymerize MMA, MAA and 3,3-(trimethoxysilyl) propyl methacrylate (MPS) in the presence of poly(MMA–MAA) seed latex particles to form the poly(MMA–MAA)/poly(MMA–MAA–MPS) core–shell latex particles. In the third step, the poly(MMA–MAA)/poly(MMA–MAA–MPS) latex particles reacted with ZnO nanoparticles, which were synthesized by a traditional sol gel method, to form the polymer/inorganic poly(MMA–MAA)/poly(MMA–MAA–MPS)/ZnO composite latex. In this study, MPS with silanol groups essentially was used as the coupling agent to couple with ZnO nanoparticles, while the results of the study showed that there was not covalent bond existed between ZnO particles and polymer latex. The ZnO particles were adsorbed on the surface of polymer latex by electrostatic interaction. Besides, the linear poly(MMA–MAA)/crosslinking poly(MMA–MAA–MPS) core–shell latex particles which were synthesized in the second step were heated in the presence of ammonia to form the hollow poly(MMA–MAA–MPS) latex particles. The factors of heating time and concentration of crosslinking agent significantly influenced the morphology of hollow poly(MMA–MAA–MPS) latex particles.     

Influence of annealing temperature on the structural and anti-corrosion characteristics of sol–gel derived,spin-coated thin films

Recently, an aqueous particulate sol–gel process using metallic chloride precursors was introduced to synthesize zirconium titanate. In this paper, the effect of annealing temperature on the structural and corrosion protection characteristics of spin-coated thin films obtained from this sol–gel system was investigated. Based on scanning electron microscopy, transmission electron microscopy, atomic force microscopy, and spectroscopic reflectometry studies, it was found that the flatness and thickness of the thin films were decreased by increasing the annealing temperature. Also, the corrosion protection of stainless steel AISI 316L provided by the prepared coatings, as analyzed by electrochemical potentiodynamic polarization experiments in a simulated body fluid, was improved in this order: 500 °C-annealed sample<900 °C-annealed sample<700 °C-annealed sample, attributed to a compromise between the defect density and the adhesion of the films to the substrate.     

Corrosion protection properties of silica coatings formed by sol–gel method on Al: The effects of acidity,withdrawal speed,and annealing temperature

In this research, silica films were coated onto aluminum sheets using the sol–gel dip-coating method from acidic and basic solutions containing (C₂H₅O)₄Si, C₂H₅OH, H₂O, and catalysts. NH₃ and HNO₃ were used as catalysts in the acidic and basic solutions, respectively. The characteristics of the films were investigated as a function of the sol catalyst, withdrawal rate, and heat treatment temperature. Morphology of the coatings was studied by scanning electron microscopy (SEM). Corrosion behavior of coated and uncoated aluminum sheets was measured in 0.1 M NaCl. Findings indicated that SiO₂ coatings can offer proper protective properties against corrosive environments. Results also showed that conditions used to prepare the coatings significantly affect the morphology and thus, the corrosion protection of the silica films.     

The electrochemistry of nitrate—amide melts: The effects of melt acidity on the discharge characteristics of lithium anodes in room temperature nitrat

Lithium anodes immersed in “neutral” nitrate—amide melts rapidly form a relatively stable passivating film. Lithium anodes polarize rapidly on the application of current densities greater than approximately 0.5 mA cm⁻². The addition of small amounts of Brønsted-Lowry acids causes rapid depassivation. Once the added acid is consumed, the anode once again passivates. In highly acidic melts, the lithium anode corrodes at a rapid rate with the evolution of NH₃, along with smaller amounts of N₂O, CO₂ and H₂O. Current densities of 1–10 mA cm⁻² can be applied with minimal anodic polarization in the acidic melts. Test cells have shown that discharge lifetime and cell voltage/current density profiles are also regulated by melt acidity. Simple test cells using lithium anodes and cerium(IV) cathodes that have open circuit voltages greater than 4 V and that can be discharged at current densities of 0.1 mA cm⁻² with minimal polarization have been demonstrated.     

Electrocatalytic characteristics of Pt–Ru–Co and Pt–Ru–Ni based on covalently cross-linked sulfonated poly(ether ether ketone)/heteropolyacids composite membranes for water electrolysis

Membrane electrode assemblies (MEAs) of covalently cross-linked sulfonated poly(ether ether ketone) (CL-SPEEK)/heteropolyacids (HPAs) composite polymer with platinum-based alloys such as Pt–Ru–Co and Pt–Ru–Ni were prepared and their electrochemical properties for water electrolysis were investigated. The HPAs, which were used in the composite membranes, were tungstophosphoric acid (TPA) (the part of TPA data was permitted by the previous authors), molybdophosphoric acid (MoPA), and tungstosilicic acid (TSiA). The MEAs with Pt–Co, Pt–Ru–Co, and Pt–Ru–Ni in the anode catalyst layer were prepared by means of a non-equilibrium impregnation–reduction (I–R) method. The electrocatalytic properties of composite membranes, such as the cell voltage and coulombic charge in CV, were in the following order: CL-SPEEK/MoPA40 > CL-SPEEK/TPA30 > CL-SPEEK/TSiA40 (wt%). For the optimum cell applications of water electrolysis, the cell voltage of Pt/PEM/Pt–Ru–Co (Electrodeposited (Dep)-MoPA) MEA with a CL-SPEEK/MoPA40 membrane was 1.70 V at 80 °C and 1 A cm^?2, and this voltage carried a value lower than that of 1.81 V of Nafion 117. In addition, the observed activity of Pt–Ru–Co (75:12:13 by EDX) is a little higher than that of Pt–Ru–Ni (79:10:11 by EDX). The mean coulombic charge and activity enhancement of Pt–Ru–Co catalysts, with and without electrodeposition, showed the same CV profiles of the Pt–Ru–Co catalysts and were in the following order: Nafion 117 < CL-SPEEK/TSiA40 < CL-SPEEK/TPA30 < CL-SPEEK/MoPA40. The current density peak of electrodeposited electrodes was a little better than those of inactivated electrodes on the same membranes. The current peak by Pt–Ru–Co with CL-SPEEK/MoPA40 (Dep-MoPA) is more than about three times as high as those of Pt electrodes on the same membranes.     

Hydrogenation of Carbon Dioxide on Rh, Au and Au–Rh Bimetallic Clusters Supported on Titanate Nanotubes, Nanowires and TiO2

Supported gold, rhodium and bimetallic rhodium-core?Cgold-shell catalysts were prepared. The supports were TiO₂ as well as titanate nanotube and nanowire formed in the hydrothermal conversion of titania. The catalytic properties were tested in the CO₂ hydrogenation at 493?K. The amount and the reactivity of the surface carbonaceous deposit were determined by temperature-programmed reduction. The surfaces of the materials were characterized by X-ray photoelectron and low-energy ion scattering spectroscopy (LEIS). The surface forms during the catalytic reaction were identified by DRIFT spectroscopy. On the XP spectra of bimetallic catalysts the existence of highly dispersed gold particles could be observed besides the metallic form on all supports. Small Rh particles could also be identified on the titanate supports. LEIS spectra demonstrated that Rh-core?CAu-shell particles formed, since no scattering from Rh was detected. The main product of CO₂ hydrogenation was CH₄ on all catalysts. IR spectra revealed the existence of CO and formate species on the surface. In addition, a new band was observed around 1,770?cm^?1 which was assigned as tilted CO. It is bonded to Rh and interacts with a nearby the oxygen vacancy of the support. Agglomeration of highly dispersed Rh was observed on bimetallic samples induced by reaction or reactant.     

Influences of crystallization temperature on the structure,dielectric, and energy storage characteristics of KBaSrNb5O15-based glass–ceramics

Glass–ceramics capacitors have great application potential in pulsed power systems, due to ultrafast discharge speed and high dielectric breakdown strength (BDS). Here, lead-free niobate glass–ceramic dielectric materials were synthesized, and the effects of heat treatment temperature on the dielectric, ferroelectric, and energy storage properties of glass–ceramics were investigated comprehensively. The results exhibit that the dielectric permittivity first increases and then decreases as the crystallinity increases; however, the dielectric BDS diminishes. At the optimum crystallization temperature of 740°C, the maximum value of discharge energy density is 2.2 J/cm³ at 600 kV/cm, which is about 7.6 times that of mother glass. Furthermore, an ultrahigh power density of about 380.9 MW/cm³ and ultrafast discharge speed of about 11.2 ns were achieved simultaneously. Meanwhile, great thermal stability of charge–discharge property was verified in this glass–ceramics. According to P–E loops and dielectric test result, a high dielectric constant (∼207) and low dielectric loss (<0.005) as well as high energy storage efficiency of about 94.9% were achieved for G740 sample. The previous results make the obtained glass–ceramic as potential candidates in dielectric capacitors.     

The influence of temperature and interface strength on the microstructure and performance of sol–gel silica–epoxy nanocomposites

A series of silica–epoxy nanocomposites were prepared by hydrolysis of tetraethoxysilane within the organic matrix at different processing temperatures, i.e., 25 and 60 °C. Epoxy matrices reinforced with 2.0–10.0 wt% silica were subsequently crosslinked with an aliphatic diamine hardener to give optically transparent nanocomposite films. Interphase connections between silica networks and organic matrix were established by in situ functionalization of silica with 2.0 wt% γ-aminopropyltriethoxysilane (APTS). The microstructure of silica–epoxy nanocomposites as studied by transmission electron microscopy indicated the formation of very well-matched nanocomposites with homogeneous distribution of silica at relatively higher temperatures and in the presence of APTS. Thermogravimetric and static mechanical analyses confirmed considerable increase in thermal stability, stiffness, and toughness of the modified composite materials as compared to neat epoxy polymer and unmodified silica–epoxy nanocomposites. A slight improvement in the glass transition temperatures was also recorded by differential scanning calorimetry measurements. High temperature of hydrolysis during the in situ sol–gel process not only improved reaction kinetics but also promoted mutual solubility of the two phases, and consequently enhanced the interface strength. In addition, APTS influenced the size and distribution of the inorganic domain and resulted in better performance of the modified silica–epoxy nanocomposites.     

The effects of MCM-41’s calcination temperature on the structure and hydrodenitrogenation over NiW catalysts

MCM-41 was calcined at 500, 560, 600 or 650 °C. It was used as support for NiW catalysts of hydrodenitrogenation (HDN) for quinoline in order to investigate the influences of the MCM-41’s calcination temperature on the structure and the HDN performance of NiW catalysts. The NiW catalysts were characterized by XRD, N₂ adsorptiondesorption, XPS, Raman, HRTEM and Py-IR techniques. The results showed that the surface area (S _BET ), the average pore diameter (Dp) and the pore volume (Vp) of the MCM-41 increased with increase of the MCM-41’s calcination temperature. The high S _BET , Dp and Vp were beneficial for the high dispersion of W species, the formation of appropriate nature of W species and acid sites on the catalysts. The HDN activity followed the order of NiW-650≈NiW-600>NiW-560>NiW-500, while the relative selectivity of HDN pathways was similar for all the catalysts.     

Influence of the temperature dependence of the thermophysical properties of coal–water fuel on the conditions and characteristics of ignition

The results of an experimental study and mathematical simulation of the ignition of coal–water fuel (CWF) particles, the main thermophysical characteristics of which (thermal conductivity (λ), heat capacity (C), and density (ρ)) depend on temperature, are reported. Based on the results of the numerical study, the influence of changes in the thermophysical properties upon the heating of the main bed of fuel on the conditions and characteristics of its ignition was analyzed. The ignition delay times (t _i) of CWF particles were determined under the typical furnace conditions of boiler aggregates. As a result of the mathematical simulation of the process of CWF ignition, it was established that the temperature dependence of thermophysical characteristics can exert a considerable effect on the characteristics and conditions of ignition. In this case, it was found that the ignition of coal–water drops is possible under the conditions of their incomplete dehydration. A good agreement of the theoretical ignition delay times of the CWF particles and the experimental values of t _i was established.     

Oxidation and reduction effects of propane–oxygen on Pd–chlorine/alumina catalysts

Pd–chloride precursor salt was used to prepare Pd/Al₂O₃ catalysts. TPSR measurements showed three distinct reactions for the oxidation of propane on palladium surface under excess of hydrocarbon: complete oxidation, steam reforming and propane hydrogenolysis. Propane oxidation on palladium catalysts was related to the Pd²⁺ sites observed on Pd/Al₂O₃ through infrared of adsorbed carbon monoxide. In fresh catalysts reduced by H₂, the IR spectra showed the linear and bridge adsorbed CO species on the Pd⁰ surface. After propane reaction, a new band at 2130 cm^-1 related to CO adsorption on Pd²⁺ species was noted. Carbon monoxide species adsorbed on Pd⁰ were also observed in all samples after reaction. Our results suggest surface ratios of Pd⁰/PdO during the propane oxidation. On the other hand, time on stream conversions of the complete oxidation of propane were affected by either the water generated during the reaction or added as a reactant at 10 vol%. The water generated by the reaction helped to eliminate chlorine residues in the form of oxychloride species leading to an increasing of the activity. However, the presence of water into the reaction mixture caused a strong decreasing of the activity. The inhibition mechanism of propane oxidation in the presence of water consisted in the dissociative adsorption of water on palladium sites with the possible formation of palladium hydroxide (Pd–OH) at the surface, diminishing the number of active surface sites. Dynamic fluctuations into the reaction conditions supported the idea that a pseudo‐equilibrium adsorption–desorption of water was reached. After water removal or increasing in the reaction temperature the equilibrium was shifted to the direction of OH–Pd decomposition. This behavior suggests that the inhibitory effect of water is a reversible phenomenon, being a function of the amount of water and the reaction temperature. This revised version was published online in July 2006 with corrections to the Cover Date.     

Low‐temperature oxidation of methane to form formaldehyde: role of Fe and Mo on Fe–Mo/SiO2 catalysts, and their synergistic effects

The partial oxidation of methane with molecular oxygen was performed on Fe–Mo/SiO₂ catalysts. Iron was loaded on the Mo/SiO₂ catalyst by chemical vapor deposition of Fe₃(CO)₁₂. The catalyst showed good low‐temperature activities at 723–823 K. Formaldehyde was a major condensable liquid product on the prepared catalyst. There were synergistic effects between iron and molybdenum in Fe–Mo/SiO₂ catalysts for the production of formaldehyde from the methane partial oxidation. The activation energy of Mo/SiO₂ decreased with the addition of iron and approached that of the Fe/SiO₂. The concentration of isolated molybdenum species (the peak at 1148 K in TPR experiments) decreased as the ion concentration increased and had a linear relationship with the selectivity of methane to formaldehyde. The role of Fe and Mo in the Fe–Mo/SiO₂ catalyst was proposed: Fe is the center for the C–H activation to generate reaction intermediates, and Mo is the one for the transformation of intermediates into formaldehyde. Those phenomena were predominant below 775 K. This revised version was published online in July 2006 with corrections to the Cover Date.     

Temperature and alkaline hydroxide treatment effects on hydrogen sorption characteristics of multi-walled carbon nanotube–graphite mixture

Temperature and alkaline hydroxide treatment effects on the surface area and pore structure of the cathode deposit multi-walled carbon nanotube (MWCNT)–graphite mixture were investigated in a temperature range of 600–800 °C. Hydrogen sorption properties of the MWCNT–graphite mixture samples were studied by varying the alkaline hydroxide-activation temperature. Pore characterization of modified MWCNT–graphite mixture was performed with the observation of adsorption–desorption isotherms of N₂ at 77 K. Hydrogen sorption of the non-treated and treated MWCNT–graphite mixture was carried out using a volumetric apparatus at 77 K. The highest surface area of the sample was obtained as 275 m² g^?1 by treatments with KOH at 600 °C. The increase in the specific surface area of MWCNT–graphite sample mixture was about 13 times. The maximum amount of hydrogen adsorbed on the MWCNT–graphite sample mixture was found as 0.75 and 0.54 wt.% by chemical treatments with KOH at 600 °C and NaOH at 700 °C, respectively whereas it was 0.01 wt.% for the original sample. The hydrogen sorption capacity was enhanced considerably by KOH treatments at 600 °C.