Thin films of GeC deposited using a unique hollow cathode sputtering technique

Experimental results on thin films of the new material Ge_xC_1−x, deposited by a unique dual plasma hollow cathode sputtering technique are presented here. The (Ge, C) system is extremely promising since the addition of C to Ge has reduced the lattice dimensions enough to allow a lattice match to silicon, while increasing the bandgap close to that of c-Si. The most important contribution of this work shows that by the non-equilibrium growth conditions present using the hollow cathode technique, one can grow Group IV materials which cannot otherwise be grown using normal CVD or MBE processes. The sputtering is accomplished by igniting a DC plasma of the Ar and H₂ gases which are fed through Ge and C nozzles, cylindrical tubes 30 mm in length with an 8 mm OD and a 3 mm ID.     

Analysis of semiconductor thin films deposited using a hollow cathode plasma torch

The hollow cathode plasma torch has been used for several years. One of the major applications has been the deposition of dielectric thin films. However, this technique has also been used to deposit metals where high-speed deposition is needed. It has proven to be useful in deposition of coatings onto the inside of substrates of complex shape, high-speed etching, and deposition of thin films at atmospheric pressure. In recent years, we have adapted the technique to deposit high-quality amorphous and polycrystalline semiconducting films. A large variety of measurement techniques have been employed to determine the film properties and the results are reported here.     

Effect of cathode active materials produced by a wet-type jet mill on lithium cell performance

We prepared slurries by dispersing LiMn₂O₄ and LiCoO₂ into toluene or NaPO₃ aqueous solution. The slurries were then milled with a high-pressure wet-type jet mill to form fine particles. In estimating the performance of Li cells containing the materials, we found that the cell capacity improved with a decrease in the materials’ particle size. Maximum cell capacity was obtained using materials produced by milling NaPO₃ slurry to reduce the particle diameter to 2-3 μm. Such the maximum value was disappeared by treating the materials with toluene. The treatment, however, did not provide remarkable increase in the cell capacity. We found that the cell cycle life tended to increase with a decrease in the mean diameter of the material particles.     

Thin films of a-SiGe:H with device quality properties prepared by a novel hollow cathode deposition technique

Using a novel hollow cathode plasma-jet reactive sputtering system in which an intense plasma, ignited in an Ar/H₂ flow, is directed through silicon and germanium nozzles, a series of a-SiGe:H thin films have been prepared on silicon and on glass substrates. These films have been optically characterized by infrared (IR) spectroscopy, surface Raman spectroscopy and spectroscopic ellipsometry (335–1000 nm). Total hydrogen concentrations, as determined by FTIR, varied with deposition conditions and ranged from 2.5×10²¹ to 1.6×10²² atom cm⁻³ and correlated with secondary ion mass spectrometry (SIMS) elemental analyses to within 10%. The ellipsometric spectra of the films have been fitted with a modified Tauc–Lorentz model for the determination of film properties, including thickness (ranging from 400 to 1100 nm) along with film uniformity and surface roughness. Conductivity measurements in the dark and under simulated AM1 solar illumination have indicated that the films grown exhibit device-quality properties. The light-to-dark conductivity ratio has consistently been greater than 1000 for films with bandgaps down to 1.3 eV. Relationships between deposition parameters, light-and-dark conductivity properties, and chemical structural features are discussed.     

New insight into the discharge process of sulfur cathode by electrochemical impedance spectroscopy

In this paper, the electrochemical reactions of sulfur cathode during discharge–charge process were investigated by EIS technique combining with XRD, SEM and EDS methods. The discharge process of the sulfur cathode could be divided into two discharge regions. These are the first discharge region (2.5–2.05 V) where the reduction of elemental sulfur to form soluble polysulfides and further reduction of the soluble polysulfides occurs, and the second discharge region (2.05–1.5 V) where the soluble polysulfides are reduced to form a Li₂S solid film covered over the carbon matrix. It was found that the EIS can distinguish the individual contributions of charge transfer resistances, ion diffusion impedance and properties originating from Li₂S film in the frequency domain of 100 kHz to 100 mHz. During the upper voltage plateau, the impedance of interfacial charge transfer dominates the reduction reaction, while during the lower voltage plateau, the mass transport in the cathode is a control step. It was also proved that the solid Li₂S appeared at the beginning of the lower voltage plateau region and became denser during the following discharge process.     

Failure analysis of novel microhollow cathode discharge microplasma reactors

Compact fuel cells are one logical progression for portable power in comparison to batteries since fuel cells have much higher energy densities. However, fuel cells have not fully entered the portable power market as they require a readily available hydrogen feed. Microplasmas offer a way to produce hydrogen portably. Microplasma reactors developed from standard semiconductor fabrication techniques, specifically microhollow cathode discharge (MHCD) devices, have been tested by our group in reforming various hydrocarbons.     

Characteristics and pathways of hydrogen produced by pulsed discharge in ethanol-water mixtures

Hydrogen produced by pulsed discharge in ethanol-water mixtures is optimized in this work. A needle-balls configuration is designed, which is fit for situ hydrogen production in transportation. The energy yield of hydrogen can attain 141.3 gH₂/kWh, which is better than most existing methods. The high energy yield attributes to the special discharge characteristics. During the discharge, shock waves make the balls jumping in the reactor that increase the randomness and local strength of discharge. The microscopic pathway of pulsed discharge in ethanol-water mixtures is also analyzed by the comparison of rate constants. The main products can be analyzed from the microscopic pathway. In addition, CH₃CHO, CH₂O are important intermediates, which may be good additives for increasing hydrogen yield.     

空心阴极气流溅射法快速沉积具有高活性光催化作用的TiO_2薄膜(下)

<正>图4a和4b分别为在UV-近红外光谱,刚沉积和经后退火工艺两种情况下的Ti O2膜。以上两种情况在可见光区域透射比几乎相同,与后退火无关。O2流量为10~50 sccm时,沉积的Ti O2膜在可见光区域具有的高透射比约为0.70。图5a为Ti O2膜在暗处停留60 min后,相应乙醛(CH3CHO)浓度与UV照射时间的关系。O2流量为10 sccm时,沉积的Ti O2膜相应CH3CHO     

Performance and emission characteristics of diesel fuel produced from waste plastic oil obtained by catalytic pyrolysis of waste polypropylene

Waste plastic oil derived from kaoline catalyzed pyrolysis of waste polypropylene is blended with diesel fuel, tested as an alternative fuel in a diesel engine, and its performance characteristics are analyzed and compared with diesel fuel operation. It is observed that the engine could operate with maximum 50% waste plastic oil blended diesel. An engine showed better performance up to 30% blend, but beyond 50% blend it gave a vibration. The results showed a stable performance with brake thermal efficiency similar to that of diesel and its value is higher up to 80% of full load. All emissions are considerably higher than that of the diesel baseline especially at high load and blend.     

Influence of the cathode porosity on the discharge performance of the lithium-oxygen battery

By varying the ratio between the amount of carbon and Kynar binder in the cathode of a lithium-oxygen battery, it could be shown that an increasing amount of binder resulted in a decrease in the discharge capacity, mainly as a result of the decrease in the cathode porosity. It was shown that the Kynar binder blocked the majority of the pores with a width below 300 Å as determined by studying the pore volume and pore size distribution by nitrogen adsorption. Three carbonate based electrolytes (PC, PC:DEC (1:1), and EC:DEC (2:1) with 1 M LiPF₆) were tested with the various cathode film compositions. Generally, the PC:DEC and EC:DEC based electrolytes provided higher capacities than PC. The results indicated that the air electrode composition and its effect on the porosity of the cathode, as well as electrolyte properties, are important when optimizing the discharge capacity.     

Experimental characterization of anode heating by electron emission from a multi-walled carbon nanotube

The steady-state temperature distribution in a thin anode bombarded by an electron beam field emitted from an individual multi-walled carbon nanotube is measured with an infrared camera, and this distribution is compared to that predicted by a numerical model. By assuming the electron distribution in the beam follows a Gaussian distribution, a good fit to the anode temperature profile is obtained and this fit provides an estimate of the beam spreading radius. Results indicate the electron beam narrows as the emission current increases. A heat flux on the anode surface as high as 0.35 W/cm² has been measured, corresponding to an electron beam radius of approximately 1.22 mm.     

Cooling by evaporation of flowing water over a hollow roof

This paper discusses the thermal modelling of the technique for cooling buildings by means of open evaporation of water over the roof. A comparative study of cooling by means of (i) a roof pond, (ii) a water spray and (iii) moving water over the roof is presented. The influences of parameters such as wind speed, relative humidity and water flow velocity on the performance of the system are numerically examined.     

Field emission from ZnO nanostructures prepared by electrodeposition

Abstract

ZnO nanostructures were synthesised on nickel metallic wires using electrodeposited method in a mixed solution of zinc nitrate [Zn(NO₃)₂] and sodium hydroxide (NaOH). Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used for characterisation. The XRD patterns revealed the formation of a wurtzite phase of ZnO only. The SEM images showed that the formation of ZnO nanostructures could be adjusted by increasing the electrolyte concentration. Field emission measurements demonstrated that ZnO nanopillars with befitting density exhibited the lowest turn on field and the highest current density. The ZnO nanostructures with field emission performance may have potentials in the future of vacuum electronic devices.     

Characterisation of charge and discharge behaviour of lithium ion batteries with olivine based cathode active material

This paper gives insight to the physical processes taking part during the two-phase transition in lithium intercalation compounds. The behaviour of olivine based electrodes is in the special focus of this work. These electrodes exhibit phase juxtaposition within the electrode particles over a wide state of charge (SOC) range. Measurements were made to explore effects related to the formation of distinct phase sequences within the particles. Asymmetric charge characteristics, a load history dependency of the internal resistance and a voltage effect related to the disappearance of certain phase regions (the later on called vanishing phase effect) were identified. Moreover, these measurements give evidence to the existence of stable phase regions inside the electrode active material. An intuitive model is given to visualize the phase regions within spherical olivine particles. Therefore an analytical approach is developed in order to take the geometry of the particles, the ion permeability as well as the size distribution of the particles in consideration. According to the developed approach and the obtained measurement results, an enhanced cell equivalent electrical circuit is evaluated, considering phase shell development effects.     

Hydrogen production by electrolysis of a phosphate solution on a stainless steel cathode

The catalytic properties of phosphate species, already shown on the reduction reaction in anaerobic corrosion of steels, are exploited here for hydrogen production. Phosphate species work as a homogeneous catalyst that enhances the cathodic current at mild pH values. A voltammetric study of the hydrogen evolution reaction is performed using phosphate solutions at different concentrations on 316L stainless steel and platinum rotating disk electrodes. Then, hydrogen is produced in an electrolytic cell using a phosphate solution as the catholyte. Results show that 316L stainless steel electrodes have a stable behaviour as cathodes in the electrolysis of phosphate solutions. Phosphate (1 M, pH 4.0/5.0) as the catholyte can equal the performance of a KOH 25%w solution with the advantage of working at mild pH values. The use of phosphate and other weak acids as catalysts of the hydrogen evolution reaction could be a promising technology in the development of electrolysis units that work at mild pH values with low-cost electrodes and construction materials.     

Ethanol production from agroindustrial biomass using a crude enzyme complex produced by Aspergillus niger

This study investigates ethanol production from simultaneous fermentation and saccharification (SFS) and separated hydrolysis and fermentation (SHS) using enzyme complexes produced by Aspergillus niger strains (ATCC 16404, ATCC 1057, ATCC 9029). The enzyme complexes were produced by solid-state fermentation (SSF) on inexpensive and readily available agroindustrial products: rice byproduct (composed of AFEX-treated rice rust and rice bran), whey and sugarcane bagasse. The ethanol was produced by Saccharomyces cerevisiae Y904 using whey and rice byproduct as the substrate and the enzyme complex produced by A. niger. The best result for solid-state fermentation (40 U/g of dry substrate, A. niger ATCC 16404) was obtained in a 0.5 L rotating drum bioreactor at 40 °C filled half filled with solid biomass composed of rice byproduct (86% wt/wt), whey (12% wt/wt) and CaCl₂ (2.0% wt/wt). The best result for ethanol fermentation (11.7 g/L of ethanol) was obtained after 12 h of SFS at pH 4.5 and 35 °C. A comparative study of ethanol production by Trichoderma reesei CCT 2768 and A. niger ATCC 16404 complexes under the same optimised SFS and SSF conditions was also performed, revealing that ethanol production by the A. niger enzyme complex was 2.25 times higher than that by T. reesei. These findings suggest that the ethanol production using crude enzymatic complexes produced by A. niger and agroindustrial biomass described in this paper is very promising in terms of disposal of the whey produced by cheese-making and other dairy food processing.     

Detailed investigation of flame transmission from a vessel to a discharge duct

The present paper deals with a problem of explosion initiated in a vessel and vented through a duct. On the basis of numerical simulation (CFD) and visualization by means of high speed camera it completes and discusses the existing results and hypotheses (especially those presented in the work of Ponizy and Leyer [1]) concerning the process of enhancement of vessel pressure rise during such an explosion. In particular, numerical simulation indicates that a secondary explosion in the duct, known as a “burn-up”, which is responsible for higher reduced explosion pressures during ducted venting, has its source in a highly turbulent zone generated at the duct entrance by the flame itself independently of the shape of the vessel/duct passage. Camera images confirm the hypothesis that the flame penetrating into the duct is strongly torn in this turbulent zone and mixed with fresh gases. On the other hand, these images show that the reverse flow created by the burn-up returns back to the vessel some amount of rapidly burning gases, which contributes to the vessel pressure increase in the same degree that the blockage of the outflow from the vessel and the intensification of combustion of the unburned mixture previously left in the vessel.     

Production of hydrogen from hydrogen sulfide assisted by dielectric barrier discharge

Hydrogen production by non-thermal plasma (NTP) assisted direct decomposition of hydrogen sulfide (H₂S) was carried out in a dielectric barrier discharge (DBD) reactor with stainless steel inner electrode and copper wire as the outer electrode. The specific advantage of the present process is the direct decomposition of H₂S in to H₂ and S and the novelty of the present study is the in-situ removal of sulfur that was achieved by operating DBD plasma reactor at ∼430 K. Optimization of various parameters like the gas residence time in the discharge, frequency, initial concentration of H₂S and temperature was done to achieve hydrogen production in an economically feasible manner. The typical results indicated that NTP is effective in dissociating H₂S into hydrogen and sulfur and it has been observed that by optimizing various parameters, it is possible to achieve H₂ production at 300 kJ/mol H₂ that corresponds to ∼3.1 eV/H₂, which is less than the energy demand during the steam methane reforming (354 kJ/mol H₂ or ∼3.7 eV/H₂).     

Heating and cooling of a building by double hollow concrete slab

This paper presents the thermal performance, in the heating and cooling of a building, of a double hollow concrete slab, one of whose faces is exposed to solar radiation and ambient air while the other is in contact with room air at constant temperature. A blackwened network of pipes is laid on the top surface and glazed sutiably. the flow rate of water / air through pipes is kept constant. It is seen that there is a time difference of 10-12 h between the maximum/ minimum of the thermal flux extering the room and the solair temperature for any flow rate. the heat flux inside the room is reduced appreciably for higher infiltration when there is no water flow to heat the building. the effect of a water film on the performance of the wall/roof has also been discussed and found to be more effective for the reduction of the heat flux coming into the building.