Showing papers in "Journal of Physics D in 2001"
TL;DR: In this article, the authors present a review of the charge carrier transport in zinc oxide and show that a physical limit due to ionized impurity scattering is reached for homogeneously doped layers, which can be attributed to the clustering of charge carriers connected with increased scattering due to the Z-2 dependence of the scattering cross section on the charge Z.
Abstract: Heavily doped zinc oxide films are used as transparent and conductive electrodes, especially in thin film solar cells. Despite decades of research on zinc oxide it is not yet clear what the lower limit of the resistivity of such films is. Therefore, the electrical parameters of zinc oxide films deposited by magnetron sputtering, metal organic chemical vapour deposition and pulsed laser ablation are reviewed and related to the deposition parameters. It is found that the lowest resistivities are in the range of 1.4 to 2×10-4 Ω cm, independently of the deposition method. The highest reported Hall mobilities are about 60 cm2 V-1 s-1. The thin film electrical data are compared with the corresponding values of single crystalline zinc oxide and with that of boron and phosphorous doped crystalline silicon. From this comparison it can be seen that the dependence of the Hall mobilities on the carrier concentration n are quite similar for silicon and zinc oxide. In the region n>5×1020 cm-3, which is most important for the application of zinc oxide as a transparent and conductive electrode, phosphorous doped silicon has a mobility only slightly higher than zinc oxide. The experimental data on the electron and hole mobilities in silicon as a function of the impurity concentration have been described by a fit function (Masetti et al 1983), which can also be applied with different fitting parameters to the available zinc oxide mobility data. A comparison of the experimental data with the well known ionized impurity scattering theories of Conwell-Weisskopf (1946) and Brooks-Herring-Dingle (1955) shows that these theories are not able to describe the data very well, even if the non-parabolic band structure is taken into account. As in the case of silicon, an additional reduction of the mobility also occurs for zinc oxide for concentrations n>5×1020 cm-3, which can be ascribed qualitatively to the clustering of charge carriers connected with increased scattering due to the Z-2 dependence of the scattering cross section on the charge Z of the scattering centre. The presented review of the charge carrier transport in zinc oxide indicates that a physical limit due to ionized impurity scattering is reached for homogeneously doped layers. Due to the universal nature of this limitation it is suggested that it also applies to the other important materials indium-tin (ITO) and tin oxide. Experiments are proposed to overcome this limit.
735 citations
TL;DR: In this paper, the physical aspects of a cross-disciplinary science and technology field: the microwave processing of materials are reviewed, including the absorption of electromagnetic waves, heat transfer and the electrodynamics of single and multimode microwave cavities.
Abstract: This article reviews the physical aspects of a cross-disciplinary science and technology field: the microwave processing of materials. High-temperature microwave processing has a clear industrial perspective in such areas as the production of advanced ceramics, the deposition of thermal barrier coatings, the remediation of hazardous wastes etc. This review starts with the relevant fundamental notions regarding the absorption of electromagnetic waves, heat transfer and the electrodynamics of single- and multimode microwave cavities. Useful formulae, estimates, and interrelations between process variables are presented. This is followed by a review of process examples illustrating the specific features of microwave processing: reduction in energy consumption and process duration, rapid and controllable heating, peculiar temperature distribution, and selectivity of energy deposition. Much attention is given to the advantages of higher-frequency millimetre-wave processing, which include the enhanced absorption in many materials of industrial interest, improved uniformity of electromagnetic energy and temperature, and the possibility of surface treatment. The phenomenon of microwave process rate enhancement is addressed in connection with the problem of the non-thermal microwave effect on mass transport in solids. Both experimental and theoretical approaches to the identification of the mechanism responsible for this effect are illustrated. Finally, the physical and technical factors influencing microwave technology scaleup and transfer to industry are discussed.
462 citations
TL;DR: In this paper, the authors proposed two methods for obtaining the atomic-like background for the x-ray absorption fine structure (XAFS): the methods of smoothing spline and of Bayesian smoothing.
Abstract: We propose two methods for obtaining the atomic-like background for the x-ray absorption fine structure (XAFS): the methods of smoothing spline and of Bayesian smoothing. Both are capable of using the prior information, calculated or experimental, about the background. The XAFS signals obtained by these techniques are shown to be significantly corrected in comparison with standard methods. The method of Bayesian smoothing is the only method that gives the errors of approximation of the atomic-like background by an artificial smooth function. These errors are shown to be the main source of the uncertainty of the XAFS function.
460 citations
TL;DR: In this paper, the merits of gas sensors for high-volume applications are discussed, including the identification of solvents and the present state of food aroma detection, as well as their application in monitoring of combustibles, especially methane, and the early detection of fires.
Abstract: Gas sensors directed to high-volume applications are discussed. Mainly semiconductor sensors cover this sector, but the merits of competing devices are shown in comparison. Chemical and physical function is elucidated by spectroscopic results and molecular calculations. Important applications, e.g. monitoring of combustibles, especially methane, and the early detection of fires, are presented as illustrations. Progress in microelectronics has enhanced the development of electronic noses. An early example of such noses, the identification of solvents and also the present state of food aroma detection are described.
421 citations
TL;DR: In this paper, a review of arc cathode spots, mainly based on the investigation of arcs in a vacuum with cold cathodes, is given, and experiments are presented that study the temporal and spatial behaviour of the spots with high time and space resolution of less than 10 ns and less than 5 µm, respectively.
Abstract: A review is given on arc cathode spots, mainly based on the investigation of arcs in a vacuum with cold cathodes. For the latter and after a short description of general features and theoretical concepts, experiments are presented that study the temporal and spatial behaviour of the spots with high time and space resolution of less than 10 ns and less than 5 µm, respectively. With the help of these observations the various spot types described in the literature are ordered into three levels: level A corresponding to the proper spot with typical diameters of 50-100 µm, level B associated with spot fragments having a size of 10-20 µm and level C comprising a substructure of the fragments. The structures undergo periodic fluctuations of brightness and position with characteristic times that can be arranged in a hierarchy from a few nanoseconds through about 100 µs. The analysis of these fluctuations shows that the spot operates in cycles that include both extremely non-stationary periods with time constants of less than 10 ns and more stationary periods in the microsecond range. In the presence of an external magnetic field, the latter periods lead to unstable plasma configurations that give rise to retrograde motion. Finally, for vacuum arc spots the basic parameters are summarized. After that, the peculiarities of spots in gases with cold electrodes are discussed, followed by a presentation of spots with hot cathodes at high pressures.
362 citations
TL;DR: In this paper, the authors used spatio-temporal cross-correlation spectroscopy (CCS) to carry out diagnostic measurements of barrier discharge (BD) in air at atmospheric pressure.
Abstract: The technique of spatially resolved cross-correlation spectroscopy (CCS) is used to carry out diagnostic measurements of the barrier discharge (BD) in air at atmospheric pressure. Quantitative estimates for electric field strength E(x,t) and for relative electron density ne(x,t)/nemax are derived from the experimentally determined spatio-temporal distributions of the luminosity for the spectral bands of the 0-0 transitions of the second positive system of N2 (λ = 337.1 nm) and the first negative system of N2+ (λ = 391.5 nm). These results are used to test the validity of some physical models of electrical breakdown in a BD. The influence of the spatio-temporal structure of the discharge on the chemical kinetics of ozone synthesis is studied by means of a semi-empirical method based on the results of spatially resolved CCS measurements.
323 citations
TL;DR: In this article, the two-photon resonances of atomic hydrogen (λ = 2×205.1 nm), atomic nitrogen, krypton, and xenon were investigated.
Abstract: The two-photon resonances of atomic hydrogen (λ = 2×205.1 nm), atomic nitrogen (λ = 2×206.6 nm) and atomic oxygen (λ = 2×225.6 nm) are investigated together with two selected transitions in krypton (λ = 2×204.2 nm) and xenon (λ = 2×225.5 nm). The natural lifetimes of the excited states, quenching coefficients for the most important collisions partners, and the relevant ratios of the two-photon excitation cross sections are measured. These data can be applied to provide a calibration for two-photon laser-induced fluorescence measurements based on comparisons with spectrally neighbouring noble gas resonances.
277 citations
TL;DR: An atmospheric pressure non-equilibrium plasma (APNEP) has been developed in the UK by EA Technology Ltd and is currently being investigated in collaboration with the University of Surrey as mentioned in this paper.
Abstract: An atmospheric pressure non-equilibrium plasma (APNEP) has been developed in the UK by EA Technology Ltd and is currently being investigated in collaboration with the University of Surrey. The main focus is the use of atmospheric pressure plasmas to modify the surfaces of commercially important polymers including polyolefins, poly(ethylene terephthalate) and poly(methyl methacrylate). These surface modifications include surface cleaning and degreasing, oxidation, reduction, grafting, cross-linking (carbonization), etching and deposition. When trying to achieve targeted surface engineering, it is vital to gain an understanding of the mechanisms that cause these effects, for example, surface functionalization, adhesion promotion or multi-layer deposition. Hence comparisons between vacuum plasma treated surfaces have also been sought with a view to using the extensive vacuum plasma literature to gain further insight. In this paper, we will introduce the APNEP and compare the key characteristics of the plasma with those of traditional vacuum plasma systems before highlighting some of the surface modifications that can be achieved by using atmospheric plasma. Data from the analysis of treated polymers (by spectroscopy, microscopy and surface energy studies) and from direct measurements of the plasma and afterglow will be presented. Finally, our current understanding of the processes involved will be given, particularly those that are important in downstream surface treatments which take place remote from the plasma source.
270 citations
TL;DR: In this article, the authors illustrate the use of an atmospheric plasma to enhance the adhesion characteristics of low-density polyethylene (LDPE) and poly(ethylene terephthalate) (PET).
Abstract: An atmospheric pressure non-equilibrium plasma (APNEP) developed in the UK by EA Technology Ltd is currently being investigated in collaboration with the University of Surrey. Of the many applications of surface modification that can be induced using plasmas, adhesion enhancement is one of the most commercially important. In this paper, we illustrate the use of an atmospheric plasma to enhance the adhesion characteristics of low-density polyethylene (LDPE) and poly(ethylene terephthalate) (PET). The polymers were treated in the remote afterglow region of an atmospheric pressure plasma to avoid the thermal effects that can cause degradation for thermally sensitive materials when placed in direct contact with the plasma. Reactive (oxygen containing) and inert (oxygen free) atmospheric plasmas rapidly impart adhesion enhancement by a factor of two to ten as measured by 180° peel tests. However, extended exposure to the atmospheric plasma does not impart additional adhesion enhancement as the surface is ablated revealing the underlying polymer with poor adhesive characteristics. In contrast, vacuum plasma treated LDPE and PET show increased adhesion with extended plasma treatment. An adhesion enhancement in excess of two to three orders of magnitude was found to be achievable for vacuum plasma treatment times greater than 10 min.
269 citations
TL;DR: Micro-thermal analysis as mentioned in this paper is a technique that uses a near-field thermal probe to exploit the benefits of using thermal excitation to select regions of a solid sample by means of surface or sub-surface imaging (atomic force microscopy or scanning thermal microscopy).
Abstract: The terms micro-thermal analysis and micro-spectroscopic analysis are used to include any form of localized characterization or analysis combined with microscopy that uses a near-field thermal probe to exploit the benefits of using thermal excitation. Individual regions of a solid sample are selected by means of surface or sub-surface imaging (atomic force microscopy and/or scanning thermal microscopy), so as to add spatial discrimination to four well-established methods of chemical fingerprinting, namely thermomechanometry, calorimetry, spectroscopy and analytical pyrolysis. We begin by describing the state of the art of scanning microscopy that uses resistive thermal probes, followed by an account of the various techniques of micro-thermal analysis. Modern materials technology is increasingly concerned with the control of materials at the mesoscale. The ability to add an extra dimension of, say, chemical composition information to high-resolution microscopy, or microscopic information to spectroscopy, plays an increasingly useful part in applied research. Micro-thermal analysis is now being used commercially to visualize the spatial distribution of phases, components and contaminants in polymers, pharmaceuticals, foods, biological materials and electronic materials. This review outlines various applications that have been described in the literature to date, the topics ranging from multi-layer packaging materials and interphase regions in composites, to the use of the technique as a means of surface treatment.
255 citations
TL;DR: In this paper, a temporally dynamic model for diffuse DBDs is introduced, from which equations were derived which allowed the calculation of internal electrical quantities in the discharge gap from measured external electrical quantities.
Abstract: Dielectric barrier discharges (DBDs) are self-extinguishing discharges due to charge accumulation on dielectric surfaces. In order to take advantage of these surface charges also at a low repetition frequency, high-voltage unipolar square pulses (amplitude up to 15 kV, rise and fall time less than 20 ns) are applied to drive DBDs. For electrical diagnostics of this novel excitation method, a temporally dynamic model for diffuse DBDs is introduced, from which equations were derived which allow the calculation of internal electrical quantities in the discharge gap from measured external electrical quantities. It was found, following a primary discharge at the rising front or at the top of the voltage pulse, that a secondary discharge is induced at the end of the falling voltage flank without simultaneously consuming energy from the external circuit. The energy needed is provided by the accumulated surface and space charges left by the primary discharge, which are totally or partially lost under normal low-frequency sine or square wave excitation. Secondary discharges are observed in a wide range of electrode configurations, gases and gas pressures for both homogeneous and filamentary discharges. In the case of filamentary modes, secondary discharges are found to develop along the remaining channels of the preceding primary discharges. Experiments for ozone synthesis show an improved energy efficiency of 8-9 eV per ozone molecule, which is about 30% better than that achieved with sine wave excitation.
TL;DR: In this article, a review summarizes current understanding of the sputtering process and the origin of the above dependences and describes how, if only a surface gradient related mechanism dominates, the evolution of surface geometry can be accurately predicted.
Abstract: Energetic ion bombardment of solid targets can lead to the production of atomic recoils and defects within the solid and the ejection or sputtering of atoms from the surface with the consequent erosion of the solid. The yield of sputtered atoms per ion depends on a number of ion and target parameters but, particularly, on the gradient of the surface with respect to the incident ion flux, the surface curvature and higher spatial derivatives of the height. As a result of these dependences of the local erosion rate, the morphology of a surface can be modified. But, in addition, surface atomic relaxation effects which may be mediated by the irradiation can occur and so the evolution of the surface may be complex. If the nature of these, often competing, processes is understood and can be suitably controlled by selection of experimental conditions, ion beam erosion can be employed to generate useful surface geometries. This review briefly summarizes current understanding of the sputtering process and the origin of the above dependences and describes how, if only a surface gradient related mechanism dominates, the evolution of surface geometry can be accurately predicted. The higher-order and surface relaxation processes are then considered in both a deterministic approach and in a stochastic approach and these are shown to lead to fine spatial scale modifications to evolving surfaces. In both these areas, the physical models are supported by experimental observations. It is then shown how the lowest and higher orders and competing mechanisms can be selected in order to produce the desired surface morphologies in several application areas, including depth profiling of impurities in solids, ion milling and polishing, and the creation of repetitive surface structures.
TL;DR: In this article, a Fourier series analysis of the dielectrophoretic force on a particle generated by this type of electrode array, for both dielectrophicoresis and travelling wave dielectricis, is presented.
Abstract: In alternating current electrokinetics, electric fields are used to generate forces on particles. Techniques have been applied for the manipulation of particles and the measurement of their dielectric properties. The fields are typically generated by microelectrode structures fabricated on planar surfaces. One particular design, using interdigitated bar electrodes, is used both in dielectrophoretic field flow fractionation and travelling wave dielectrophoresis. This paper presents a Fourier series analysis of the dielectrophoretic force on a particle generated by this type of electrode array, for both dielectrophoresis and travelling wave dielectrophoresis. Simple expressions are derived for the force at a distance of the order of the electrode spacing from the electrodes. A full analytical expression is given for the dielectrophoretic force in two dimensions. Comparisons are made with previously published experimental observations.
TL;DR: In this paper, the nonlinear optical parameters of Au, Ag, Pt and Cu colloidal solutions using the Z-scan method and third-harmonic generation (THG) are presented.
Abstract: The investigations of the nonlinear optical parameters of Au, Ag, Pt and Cu colloidal solutions using the Z-scan method and third-harmonic generation (THG) are presented. The nonlinear refractive indices, nonlinear absorption coefficients and Kerr-induced nonlinear susceptibilities (χ(3)(-ω;ω,-ω,ω)) of these solutions on the wavelengths of picosecond and nanosecond Nd:YAG laser radiation (λ = 1064 nm) and its second harmonic (λ = 532 nm) have been measured. A tenfold increase of nonlinear susceptibilities on the wavelength of 532 nm in comparison with λ = 1064 nm is shown for these colloidal metals. The application of colloidal metals as optical limiters of picosecond and nanosecond radiation (λ = 1064 nm and 532 nm) was studied. The influence of aggregation of colloidal clusters on optical limiting in these media was considered. It was shown that the appearance of the long-wave wing of absorption at the final stages of aggregation led to the nonlinear absorption of picosecond pulses. The investigations of the THG of picosecond Nd:YAG laser radiation in colloidal metals (Pt and Cu) are presented. THG efficiency was found to be 7×10-7 for colloidal platinum. Nonlinear susceptibilities χ(3)(-3ω;ω,ω,ω) of colloidal platinum and copper were measured to be (1.5±0.75)×10-14 esu and (1±0.5)×10-14 esu, respectively.
TL;DR: In this article, a simple model for the dependence of thermal lensing and degradation in beam quality on the transverse intensity profile of the pump beam is presented, and the role of energy transfer upconversion as a mechanism for additional heat loading under non-lasing conditions is considered.
Abstract: Degradation in beam quality due to aberrated thermal lensing and depolarization loss due to stress induced birefringence in end-pumped edge-cooled solid-state lasers are investigated. A simple model for the dependence of thermal lensing and degradation in beam quality on the transverse intensity profile of the pump beam is presented. Experimental measurements of thermal lensing, degradation in beam quality and depolarization loss in a diode-bar-end-pumped Nd:YAG rod support the main predictions of the model and, in addition, show that there can be significant extra heating under non-lasing conditions compared to lasing conditions. The role of energy transfer upconversion as a mechanism for additional heat loading under non-lasing conditions is considered. Finally, various strategies for limiting the impact of thermal lensing and thermally induced birefringence on laser performance in simple end-pumped cavity configurations are reviewed.
TL;DR: In this paper, the presence of negative ions and metastable species in low-pressure high-density oxygen discharges was studied and the negative oxygen ion O- was found to be the dominant negative ion in the discharge.
Abstract: We use a global (volume averaged) model to study the presence of negative ions and metastable species in low-pressure high-density oxygen discharges. We find the negative oxygen ion O- to be the dominant negative ion in the discharge, the density of the negative ion O2- to be small and the density of the negative ion O-3 to be negligible in the pressure range of interest, 1-100?mTorr. Dissociative attachment of the oxygen molecule in the ground-state O2(3?g-) and the metastable oxygen molecule O2(a1?g) are the dominating channels for the creation of the negative oxygen ion O-. At low pressure (<5?mTorr) recombination involving O- and O+ ions is the main loss channel for O- ions. At higher pressure, the detachment on O(3P) becomes the main loss channel for the O- ion. The creation of O-2 is mainly through dissociative attachment of ozone O3. Ozone is almost entirely created through detachment by the collision of O- with the metastable oxygen molecule O2(a1?g). The creation of O-2 is thus greatly influenced by this detachment process and neglecting the detachment has a significant influence on the density of O-2 ions. At low pressure (<10?mTorr) the O-2 ion is mainly lost through recombination while at higher pressure the charge transfer to form O2 is the dominating loss process.
TL;DR: In this paper, the authors developed a technique to address the problem of feature size control at the interface of the ICP etch tool, which is an industry wide problem in microelectro-mechanical applications.
Abstract: Dry etching of Si is critical in satisfying the demands of the micromachining industry. The micro-electro-mechanical systems (MEMS) community requires etches capable of high aspect ratios, vertical profiles, good feature size control and etch uniformity along with high throughput to satisfy production requirements. Surface technology systems' (STS's) high-density inductively coupled plasma (ICP) etch tool enables a wide range of applications to be realized whilst optimizing the above parameters. Components manufactured from Si using an STS ICP include accelerometers and gyroscopes for military, automotive and domestic applications. STS's advanced silicon etch (ASETM) has also allowed the first generation of MEMS-based optical switches and attenuators to reach the marketplace. In addition, a specialized application for fabricating the next generation photolithography exposure masks has been optimized for 200 mm diameter wafers, to depths of ~750 µm. Where the profile is not critical, etch rates of greater than 8 µm min-1 have been realized to replace previous methods such as wet etching. This is also the case for printer applications. Specialized applications that require etching down to pyrex or oxide often result in the loss of feature size control at the interface; this is an industry wide problem. STS have developed a technique to address this. The rapid progression of the industry has led to development of the STS ICP etch tool, as well as the process.
TL;DR: In this article, a review of the properties of thermal plasmas in mixtures of different gases is presented, with particular attention given to the calculation of diffusion coefficients, which is a significant problem in mixed-gas mixtures.
Abstract: The calculation and measurement of the properties of thermal plasmas in mixtures of different gases are reviewed. The calculation of composition, thermodynamic properties and transport coefficients is described. Particular attention is given to the calculation of diffusion coefficients, which is a significant problem in mixed-gas plasmas. The combined diffusion coefficient formulation is shown to be a useful method for the treatment of diffusion. Computational fluid dynamic modelling of thermal plasmas in gas mixtures is considered, using the examples of demixing in welding arcs, the turbulent mixing of atmospheric air into a plasma jet and a plasma waste destruction process. Diagnostic techniques for mixed-gas plasmas, in particular emission spectroscopy, laser scattering and laser-induced fluorescence, are discussed.
TL;DR: In this article, the mechanisms of charge injection, transport and trapping in low-density, high-density and cross-linked polyethylene (LDPE, HDPE and XLPE) are investigated through charging-discharging current measurements and space-charge observations.
Abstract: The mechanisms of charge injection, transport and trapping in low-density, high-density and cross-linked polyethylene (LDPE, HDPE and XLPE) are investigated in this paper through charging-discharging current measurements and space-charge observations. The conductivity of LDPE is much larger than that of XLPE and HDPE. The threshold for space-charge accumulation and that for a space-charge-limited current mechanism, coinciding for the same material, are almost identical for LDPE and HDPE, while the threshold of XLPE is higher. However, HDPE accumulates more charge than the other two materials. The depolarization space-charge curves and the conduction current versus field characteristics indicate that the mobility of LDPE is larger than that of XLPE and HDPE, which supports the significant difference in conductivity. The lower mobility, as well as the nature, depth and density of trap sites, can explain the difference in space-charge accumulation and thresholds.
TL;DR: In this paper, the influence of the corona-charging process on the piezoelectric transducer coefficient d33 of a cellular electret film has been investigated, and the effect of the gas inside the voids has also been studied.
Abstract: The influence of the corona-charging process on the piezoelectric transducer coefficient d33 of a cellular electret film has been investigated. An increased corona voltage can be considered as a way to enhance the charge density and thus also the resulting piezoelectric effect. Higher corona-charging voltages are possible with increased ambient pressure or in suitable dielectric gases. The effect of the gas inside the voids has also been studied. Enhanced transducer coefficients were obtained by corona charging in N2 or N2O gas atmospheres at 100-450 or 100-140 kPa pressures, respectively. The highest transducer coefficients of about 790 pCN-1 were obtained when N2 gas was filled into the voids of a cellular polymer film by means of consecutive vacuum and high-pressure treatments at 295 or 313 K.
TL;DR: In this paper, the authors presented the preparation and study of PZT-PVDF composites of 0-3 connectivity, which were prepared by two methods, namely (i) the solvent-cast method and (ii) the hot-press method.
Abstract: The most widely used material for active transducer applications is the ferroelectric ceramic PZT. Composites made of ferroelectric ceramics combined with polymers have several advantages over pure ceramics. Diphasic composites of PZT (and La/Ca modified PZT) combined with various polymers such as PVDF, PVC, PVA, epoxy resin and co-polymers have been widely studied and reported in the literature. In this paper we present the preparation and study of PZT-PVDF composites of 0-3 connectivity. The composites are prepared by two methods, namely (i) the solvent-cast method and (ii) the hot-press method. The piezoelectric strain coefficient (d33) is studied as a function of volume fraction of PZT in PVDF. The dielectric constant (k) is measured as a function of temperature and the piezoelectric voltage coefficient (g33) of the composite is determined. The experimental values of the dielectric constant, d33 and g33 of the composites are compared with the earlier reported values and the theoretical values proposed by Furukawa et al (Furukawa T, Ishida K and Fukada E 1979 J. Appl. Sci. 50 4904) and Bhimasankaram et al (Bhimasankaram T, Suryanarayana S V and Prasad G P 1998 Curr. Sci. 4 967). The composite with 0.5 PZT volume fraction prepared by the hot-press method is found to possess a reasonably high d33 value and exhibit good flexibility and stability with time.
TL;DR: In this paper, optical photo-induced second harmonic generation in pyrene molecular crystals photoinduced by intrinsic defects is investigated and a correlation between the number of macro-vacancies (defects) measured by positron annihilation and second-order nonlinear optical susceptibilities indicates the appearance of additional non-centrosymmetry in the electron charge density distribution caused by the defects.
Abstract: We have found optical photoinduced second harmonic generation in pyrene molecular crystals photoinduced by intrinsic defects. A correlation between the number of macro-vacancies (defects) measured by positron annihilation and second-order nonlinear optical susceptibilities indicates the appearance of additional non-centrosymmetry in the electron charge density distribution caused by the defects. Simultaneously, changes in the kinetics of phenomena in the picosecond time regime are demonstrated. The latter indicate the essential role of intra- and intermolecular contributions in the observed phenomena.
TL;DR: In this paper, the effect of the electron distribution in front of the cathode-directed streamer head on the characteristics of the discharge itself has been analyzed and the analytical model that allows us, with the use of the known streamers head potential, to obtain associated values of the head radius and peak electric field strength has been proposed and verified.
Abstract: The effect of the electron distribution in front of the cathode-directed streamer head on the characteristics of the discharge itself has been analysed in this paper. Both the process of gas photoionization in front of the streamer head and the effect of spatially uniform `background' pre-ionization have been taken into consideration. It is shown that the substitution of the actual photoelectron distribution in front of the streamer head for uniform `background' pre-ionization makes it possible, by the variation of this parameter, to attain the coincidence of some characteristics of the streamer discharge (streamer velocity, conduction current, electron distribution in the streamer head and channel), not allowing for coincidence of all the characteristics simultaneously in this case. The analytical model that allows us, with the use of the known streamer head potential, to obtain associated values of the head radius and peak electric field strength has been proposed and verified.
TL;DR: In this paper, a multispark electric discharge in water excited along multielectrode metal-dielectric systems with gas supply into the interelectron gaps is investigated.
Abstract: Results are presented from investigations of multispark electric discharge in water excited along multielectrode metal-dielectric systems with gas supply into the interelectrode gaps. The intensity distribution of discharge radiation in the region covering the biologically active soft UV (190≤λ≤430 nm) has been determined and the absolute number of quanta in this wavelength interval has been measured. The potentiality of the slipping surface discharge in water for its disinfection is analysed. The energy expenditure for water cleansing is estimated to be as low as ~10-4 kWh l-1.
TL;DR: In this paper, the role played by the N2(A3Σu+) metastable on the overall kinetics of N2 and N2-O2 stationary discharges is illustrated by using a kinetic model based on the selfconsistent solutions to the Boltzmann equation coupled to the rate balance equations for the vibrationally and electronically excited molecules, atoms and charged particles, in which the sustaining electric field is self-consistently determined.
Abstract: The role played by the N2(A3Σu+) metastable on the overall kinetics of N2 and N2-O2 stationary discharges is illustrated by using a kinetic model based on the self-consistent solutions to the Boltzmann equation coupled to the rate balance equations for the vibrationally and electronically excited molecules, atoms and charged particles, in which the sustaining electric field is self-consistently determined It is shown that together with the vibrational distribution of N2(X1Σg+,v) molecules, the metastable state N2(A3Σu+) plays a central role in the whole problem, since some important aspects of these discharges, such as ionization, gas phase chemistry and gas heating are associated with different processes involving the N2(A3Σu+) state
TL;DR: In this article, chemical bath deposition was used to prepare antimony trisulfide (Sb2S3) thin films, of different particle size and with noticeably different band gaps, onto glass substrates.
Abstract: Chemical bath deposition was used to prepare antimony trisulfide (Sb2S3) thin films, of different particle size and with noticeably different band gaps, onto glass substrates. The structural investigations revealed that the as-deposited films are amorphous in nature. The particle size determined from the intercept method using SEM micrographs increases from 20 nm to 100 nm as the duration of the deposition increases. The optical absorption edge shifted from the bulk energy gap of 2.2 to 3.8 eV on decreasing the particle size. This phenomenon is interpreted in terms of the quantum size effect of electrons and holes in Sb2S3 nanoparticles. The optical constants of the Sb2S3 thick films (589 nm) were determined from the interference maxima and minima in the wavelength range 400-2500 nm using the Swanepole method. The Wemple-DiDmenico single-oscillator model parametrizes the refractive index.
TL;DR: In this article, the rotational temperature of the first negative system (transitions N+2(B→X)) depends on the nitrogen partial pressure pN2 and increases up to 600 K at high pN 2 while that of the second positive system (Transitions N2(C→B)) is equal to 310±10 K for all discharge conditions.
Abstract: In dielectric barrier discharges in helium-nitrogen mixtures of 1 bar the rotational temperature of the first negative system (transitions N+2(B→X)) depends on the nitrogen partial pressure pN2 and increases up to 600 K at high pN2 while that of the second positive system (transitions N2(C→B)) is equal to 310±10 K for all discharge conditions. This difference comes from two different classes of excitation processes: `fast' reactions mainly of He metastables and ions during or immediately after the active microdischarge, i.e. in a hot environment, and `slow' reactions of the metastable N2(A3Σ+u) state. Chemical reactions in general determine the effective lifetimes of the metastables. The long-living nitrogen metastables diffuse far away from the microdischarge area and react in the (cool) ambient gas. For the various discharge conditions we evaluated, from absolutely measured line intensities, the concentrations of N2(A3Σ+u), NO, and OH (formed as a consequence of surface reactions) as functions of the average discharge power and estimated the electron density in the discharge. The variation of the measured rotational temperature of the first negative system with pN2 can be attributed to changes of the gas heating and, consequently, the gas dynamics in the microdischarges.
TL;DR: In this paper, the authors report NOx removal via reduction processes using two types of combined system of pulse corona discharge and catalysts: the single-stage plasma-driven catalyst (PDC) system, and the two-stage selective catalytic reduction (PE-SCR) system.
Abstract: In this paper, we will report NOx removal via reduction processes using two types of combined system of pulse corona discharge and catalysts: the single-stage plasma-driven catalyst (PDC) system, and the two-stage plasma-enhanced selective catalytic reduction (PE-SCR) system. Several catalysts, such as γ-alumina catalysts, mechanically mixed catalysts of γ-alumina with BaTiO3 or TiO2, and Co-ZSM-5 were tested. In the PDC system, which is directly activated by the discharge plasma, it was found that the use of additives was necessary to achieve NOx removal by reduction. Removal rates of NO and NOx were linearly increased as the molar ratio of additive to NOx increased. The dependence of NO and NOx removal on the gas hourly space velocity (GHSV) at a fixed specific input energy (SIE) indicates that plasma-induced surface reaction on the catalyst plays an important role in the PDC system. It was found that the optimal GHSV of the PDC system with the γ-alumina catalyst was smaller than 6000 h-1. Mechanical mixing of γ-alumina with BaTiO3 or TiO2 did not enhance NO and NOx removal and γ-alumina alone was found to be the most suitable catalyst. The dielectric constant of the catalyst only influenced the plasma intensity, not the NOx removal. In the PE-SCR system, plasma-treated NOx (mostly NO2) was reduced effectively with NH3 over the Co-ZSM-5 catalyst at a relatively low temperature of 150 °C. Under optimal conditions the energy cost and energy yield were 25 eV/molecule and 21 g-N (kWh)-1, respectively.
TL;DR: In this paper, the influence of anode geometry, anode resistivity, inter-electrode distance and gas flow on the threshold currents that mark the corona-toglow and glow-to-spark transitions is investigated.
Abstract: In negative corona discharges in ambient air different discharge modes can be observed. In this paper the discharge current regions corresponding to these modes are determined. The influence of anode geometry, anode resistivity, inter-electrode distance and gas flow on the threshold currents that mark the corona-to-glow and glow-to-spark transitions is investigated. The experimental data are backed up by an analytical treatment of ionization instability development within a local current spot on metallic and resistive anodes.
TL;DR: In this article, an Xe excimer barrier discharge lamp was used to generate a discharge with a much lower electron density than that possible using ac. The spectral characteristics are similar to that observed using ac excitation except that the ratio of VUV to visible Xe* emission increases by a factor of three.
Abstract: We observe marked increases in the time-averaged intensity, peak intensity, efficiency and spectral purity of the VUV output from an Xe excimer barrier discharge lamp when using short-pulse (~150 ns FWHM (full width half maximum)) excitation. Intensity increases with Xe pressure up to 600 Torr with a maximum output 2.6 times higher and an efficiency 3.2 times higher than the same lamp excited by conventional ac excitation (i.e. sinusoidal voltage waveform). The output occurs in regular short pulses (<300 ns FWHM) with a peak intensity more than six times the peak intensity typically obtained using ac. The spectral characteristics are similar to that observed using ac excitation except that the ratio of VUV to visible Xe* emission increases by a factor of three. The pulsed discharge appears diffuse (i.e. glow-like), even at the higher pressures at which the ac discharge is filamentary. It is concluded that the enhanced performance results largely from the ability for pulsed excitation to generate a discharge at near atmospheric pressures with a much lower electron density than that possible using ac.