Plasma sterilization using the RF glow discharge

In the present work, glow discharge oxygen plasma was used to sterilize the Pseudomonas aeruginosa on the polyethylene terephthalate (PET) sheets. In a self-designed plasma reaction equipment, active species (electron, ion, radical, UV light, etc.) were separated effectively, and the discharge area, afterglow area and remote area were plotted out in the plasma field. Before and after plasma treatment the cell morphology was studied by scanning electron microscopy (SEM). The results showed that after treatment of 30 s the germicidal effect is 4.26, 3. 84, 2.61, respectively in the three areas on the following conditions: discharge power was 40 W and gas flux was 20 cm³/min. SEM results revealed the cell morphology before and after plasma treatment. The walls or cell membrane cracking was testified by determining the content of protein using coomassie light blue technique. The results from electron spin resonance spectroscopy (ESR) and double Langmuir electron probe showed that electron, ion and oxygen free radical played important roles in sterilization in the discharge area, but only oxygen radicals acted to sterilize the bacteria in the afterglow area and the remote area.     

Analysis of sterilization effect by pulsed dielectric barrier discharge

Atmospheric pressure (AP) plasmas can sterilize against almost all kinds of bacteria because many ions and reactive species, such as oxygen atoms and ozone, etc., are generated during AP plasmas. So AP plasmas are proper processes for application to air cleaners and sterilizers. The aim of this paper is to evaluate a germicidal effect caused by pulsed plasma system in air utilizing a dielectric barrier discharge (DBD) type reactor incorporating alumina, glass, etc. Escherichia coli, Bacillus subtilis and Pseudomonas aeruginosa bacteria were used for this sterilization experiment. For analysis of the relationship between sterilization results and chemical species generated in the discharge, we used optical emission spectroscopy and we checked emission spectra by atomic oxygen (394.2 and 436.8 nm) and second positive system of nitrogen (337.1 nm). Experimental results showed that DBD treatment during 70 s sterilized E. coli with 99.99% effectively and ozone molecules were the dominant germicidal species. From these results we concluded that the pulsed DBD system is very effective for sterilization.     

A multi-wire-to-cylindrical type packed-bed plasma reactor for the inactivation of M. aeruginosa

Eutrophication in drinking water supplies brings about serious impact on the drinking water safety. In this study, a new multi-wire-to-cylindrical type packed-bed plasma reactor has been proposed and experimentally investigated its ability to control excessive growth of Microcystis aeruginosa (M. aeruginosa). Experimental results show the removal efficiency of M. aeruginosa and the inactivation constant were increased with the increased electrode number and air flow rate. More than 93% of optical density was removed at an air flow rate of 0.75 m³/h with treatment for 40 min at the end of the fifth day and the inactivation constant 16.20 was obtained in the multi-wire-to-cylindrical type packed-bed plasma reactor with 3 mm diameter 6-wire high-voltage electrodes; the difference in the electrode material on the removal efficiency of M. aeruginosa was unobvious, but the effects of pulse repetitive rate and applied peak pulse voltage on the inactivation of M. aeruginosa were significant. The changes in the visible spectra of M. aeruginosa solution demonstrated that photosynthetic pigments, such as chlorophyll-a, phycocyanins, carotenoids have been damaged, indicating the inhibitive behaviors of discharge on the algal growth. These results implicate that M. aeruginosa cells were inactivated by a multi-wire-to-cylindrical type packed-bed plasma reactor, demonstrating the considerable potential of such an alternative process for efficient water purification.     

Carbon fiber formation in electrical discharges in hydrocarbons

The process of synthesis of carbon fiber from hydrocarbon vapours in low-current electrical-discharge plasma was investigated in the paper. The carbon fibers were effectively synthesised in discharge of positive polarity generated between a stainless steel needle and a plate made of nickel alloy, for the discharge current ranged from 1 mA up to 3 mA. The experiments were carried out at normal pressure in cyclohexane vapours with argon as carrier gas. The diameter of produced fibers varied from about 20 to 70 μm. The growth rate of the fiber was about 0.25 mm/s.     

Experimental transition probabilities in the Ar III and Ar IV UV spectra

We present transition probabilities (Einstein's A values) for 38 Ar III (doubly ionized argon) and 14 Ar IV (triply ionized argon) spectral lines from the wavelength interval 240–308 nm. Considered spectral lines are recorded in laboratory pulsed discharge. The relative line intensity ratio procedure has been applied in evaluation of transition probabilities. As a reference for transition probability evaluation we have chosen A value of 241.884 nm spectral line in Ar III spectrum and A value of 280.947 nm in Ar IV spectrum, both obtained theoretically. Careful analysis of experimental and existing theoretical data is conducted in order to deduce uncertainties. Presented Ar III and Ar IV A values are for the first time obtained relying on experimental data.     

Influence of argon ambience on the structural,morphological and optical properties of pulsed laser ablated zinc sulfide thin films

Nanostructured zinc suplhide thin films are successfully deposited on quartz substrates using pulsed laser deposition (PLD) under different argon pressures (0, 5, 10, 15 and 20 Pa). The influence of argon ambience on the microstructural, optical and luminescence properties of zinc sulfide (ZnS) thin films is systematically investigated. The GIXRD data suggests rhombohedral structure for ZnS films prepared under different argon ambience. Self-assembly of grains into well-defined patterns along the y direction is observed in the AFM image of the film deposited under argon pressure 20 Pa. All the films show a blue shift in optical band gap. This can be due to the quantum confinement effect and less widening of conduction and valence band for the films with less thickness and smaller grain size. The PL spectra of the different films are recorded at excitation wavelengths 250 nm and 325 nm and the spectra are interpreted. The PL spectra of the films recorded at excitation wavelength 325 nm show intense yellow emission. The film deposited under an argon pressure of 15 Pa shows the highest PL intensity for excitation wavelength 325 nm. For the PL spectra (excitation at 250 nm), the highest PL intensity is observed for the film prepared under argon free ambience. In our study, 15 Pa is the optimum argon pressure for better crystallinity and intense yellow emission when excited at 325 nm.     

Deposition of device quality amorphous silicon and solar cell from argon dilution of silane

In our present study hydrogenated amorphous silicon (a-Si:H) thin films and solar cells have been prepared in a conventional single chamber rf-PECVD unit from silane–argon mixture by varying radio frequency (rf) power densities from 6 mW/cm² to 50 mW/cm². By optimizing the properties of the intrinsic material we have chosen a material which is deposited at 6 mW/cm² rf power density, 0.2 Torr pressure, 175 ^oC substrate temperature and by 97% argon dilution. For this material minority carriers (holes) diffusion length (L_d) measured in the as deposited state is 180 nm and it degrades by 15% after light soaking. This high L_d value indicates that the material is of device quality. We have fabricated a single junction solar cell having the structure p-a-SiC:H/i-a-Si:H/n-a-Si:H without optimizing the doped layers. This set exhibits a mean open circuit voltage of 0.8 V and conversion efficiency of 7.7%. After light soaking conversion efficiency decreases by 15% which demonstrates that it is possible to deposit device grade material and solar cells from silane–argon mixture.     

Near limit behavior of the detonation velocity

The behavior of the detonation velocity near the limits is investigated. Circular tubes of diameters 65, 44 and 13 mm are used. To simulate a quasi two-dimensional rectangular geometry thin annular channels are also used. The annular channels are formed by a 1.5 m long insert of a smaller diameter tube into the larger outer diameter detonation tube. Premixed mixtures of C₂H₂ + 2.5O₂ + 70%Ar, CH₄ + 2O₂ and C₂H₂ + 5N₂O + 50%Ar are used in the present study. The high argon dilution stoichiometric C₂H₂ + 2.5O₂ mixture has a regular cell size and piecewise laminar reaction zone and thus referred to as “stable”. The other two mixtures give highly irregular cell pattern and a turbulent reaction zone and are hence, referred to as “unstable” mixtures. Pressure transducers and optical fibers spaced 10 cm apart along the tube are used for pressure and velocity measurements. Cell size of the three mixtures studied is also determined using smoked foils in both the circular tubes and annular channels. The ratio d/λ (representing the number of cells across the tube diameter) is found to be an appropriate sensitivity parameter to characterize the mixture. The present results indicate that well within the limit, the detonation velocity is generally a few percent below the theoretical Chapman–Jouguet (CJ) value. As the limit is approached, the velocity decreases rapidly to a minimum value before the detonation fails. The narrow range of values of d/λ of the mixture where the velocity drops rapidly is found to correspond to the range of values for the onset of single headed spinning detonations. Thus we may conclude that the onset of single headed spin can be used as a criterion for defining the limits. Spinning detonations are also observed near the limits in annular channels.     

Heterogeneous sono-Fenton-like process using nanostructured pyrite prepared by Ar glow discharge plasma for treatment of a textile dye

The plasma-treated pyrite (PTP) nanostructures were prepared from natural pyrite (NP) utilizing argon plasma due to its sputtering and cleaning effects resulting in more active surface area. The NP and PTP were characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Brunauer–Emmett–Teller (BET) and scanning electron microscopy (SEM) methods. The performance of the PTP was greater than NP for treatment of Reactive Red 84 (RR84) by the heterogeneous sono-Fenton process. The optimum amounts of main operational parameters were obtained as PTP of 4 g/L, initial dye concentration of 10 mg/L, pH of 5, and ultrasonic power of 300 W after 120 min of reaction time. Also, the effects of enhancers, and inorganic salts and t-butanol as hydroxyl radical scavengers on the degradation efficiency were investigated. Gas chromatography–mass spectroscopy analysis (GC–MS) was applied for detection of some degradation intermediates. Environmentally friendly plasma modification of the NP, in situ production of H₂O₂ and OH radicals, low leached iron concentration and repeated reusability at the milder pH are the significant benefits of the PTP utilization.     

Ar plasma waveguide produced by a low-intensity femtosecond laser

Using the interaction of a low-intensity femtosecond laser pulse (30 fs, 6 × 10¹⁵ Wcm^? 2) with argon cluster jet produced from a slit nozzle, we experimentally probe the formation of a uniform plasma waveguide by the interferogram analysis. The results about evolution of plasma channel demonstrate that it is feasible to produce the plasma waveguide for an fs laser pulse of low-intensity. It takes tens of nanoseconds to form a plasma waveguide. The simulation by one-dimensional Gaussian plasma hydrodynamic expansion model indicates that the temperature of plasma channel is not high under this condition. Thus it takes tens of nanoseconds to form a plasma waveguide.     

Comparative ultrastructure of spermatozoa of the redclaw Cherax quadricarinatus and the yabby Cherax destructor (Decapoda,Parastacidae)

Ultrastructure of spermatozoa of redclaw Cherax quadricarinatus and yabby Cherax destructor were described and compared. The acrosome complex and nucleus are located at the anterior and posterior region of the spermatozoon, respectively. The acrosome is a complex vesicle divided into two parts: the main body of the acrosome appears as a dense cup-shaped structure in longitudinal sagittal view, with the subacrosome zone occupying the central area of the vesicle. The acrosome is larger in C. quadricarinatus (width 2.37 ± 0.27 μm, length 1.31 ± 0.23 μm) than in C. destructor (width 1.80 ± 0.27 μm, length 1.01 ± 0.15 μm). There was no significant difference in L:W ratios of the studied species. The subacrosome zone in both species consists of two areas of different electron density. The nucleus is substantially decondensed and irregular in shape, with elaborate extended processes. The examined species exhibited a well-conserved structure of crayfish spermatozoon, similar to those of Cherax cainii and Cherax albidus. Small acrosome size, the absence of radial arms, and an extracellular capsule seem to be the morphological features that mostly distinguish Cherax from the Astacidae and Cambaridae.     

Hydrothermal synthesis of self-emitting Y(V,P)O4 nanophosphors for fabrication of transparent blue-emitting display device

Self-emiting Y(V_x,P_1?x)O₄ blue nanophosphors with various compositons (x=0.1–0.9) were synthesized by a facile hydrothermal route and subsequently annealed at different temperatures of 800–1100 °C for 2 h. A higher content of vanadate in Y(V,P)O₄ nanophosphors resulted in a larger particle growth upon annealing. The blue luminescence under a vacuum ultraviolet excitation increased with an increasing phosphate content. Considering the size and luminescence, Y(V_0.1,P_0.9)O₄ nanophosphors annealed at 800, 1000, and 1100 °C were used for the formation of transparent blue emissive layer. Nanophosphor layer was uniformly deposited on glass substrate by a screen-printing. ～0.9 μm thick nanophosphor layer that was prepared with 1000 °C-annealed Y(V_0.1,P_0.9)O₄ nanophosphor showed a high visible transmittance value of 78%. Transparent blue-emitting test panel of plasma display was simply fabricated using nanophosphor layer/glass as a rear panel and combining it with the front panel used in the current plasma display panel, and their discharge luminance properties were discussed.     

Escherichia coli deactivation study controlling the atmospheric pressure plasma discharge conditions

Bio-applications of plasma have been widely studied in recent years. However, considering the high interests, the inactivation mechanisms of micro-organisms by plasma have not been clearly explained. The goal of this study was to find the sterilization mechanisms and define the major sterilization factors with the atmospheric pressure radio-frequency helium glow discharge. For the sterilization target the Escherichia coli was used. To begin with the sterilization study, the plasma characteristics were investigated by means of electrical and optical diagnostics. Especially, the gas temperature was controlled under 50 °C by keeping the input power less than 70 W to eliminate the thermal effects. Contribution of the UV irradiation from the plasma was studied and it turned out to be negligible. On the other hand, it was found that the sterilization was more effective up to 40% with only 0.15% oxygen addition to the helium supply gas. It indicates that the inactivation process was dominantly controlled by oxygen radicals, rather than heat or UV photons.     

Microhardness of a dental restorative composite resin containing nanoparticles polymerized with argon ion laser

The objective of this study was to compare the microhardness of two resin composites (microhybrid and nanoparticles). Light activation was performed with argon ion laser 1.56 J (L) and halogen light 2.6 J (H) was used as control. Measurements were taken on the irradiated surfaces and those opposite them, at thicknesses of 1, 2 and 3 mm. To evaluate the quality of polymerization, the percentages of maximum hardness were calculated (PMH). For statistical analysis the ANOVA and Tukey tests were used (p ≤ 0.05). To microhybrid was shown that the hardness with laser was inferior to the hardness achieved with halogen light, for both the 1 mm and 2 mm. The nanoparticles polymerized with laser, presented lower hardness even on the irradiated surface, than the same surface light activated with halogen light. The microhybrid attained a minimum PMH of 80% up to the thickness of 2 mm with halogen light, and with laser, only up to 1 mm. The nanoparticles attained a minimum PMH of 80% up to 3 mm thickness with halogen light and with laser this minimum was not obtained at any thickness. Based on these results, it could be concluded that light activation with argon ion laser is contra-indicated for the studied nanoparticles.     

Resonances in the final Rydberg state population of multiply charged ions ArVIII,KrVIII, and XeVIII escaping solid surfaces

The appearance of resonances (pronounced maxima at n_A = n_res) in the probability distributions for the population of the Rydberg state (n_A, l_A, m_A) of multiply charged ions (Z ? 1) escaping solid surfaces at intermediate velocities (v ≈ 1 a.u.) is discussed. Within the framework of the time-symmetrized two-state vector model, in which the state of a single active electron is described by two wave functions Ψ₁ and Ψ₂, the resonances are explained by means of an electron tunneling in the very vicinity of the ion–surface potential barrier top. To include this specific feature of electron transitions into the model, the appropriate etalon equation method is used in the calculation of the function Ψ₁. We consider the ions ArVIII, KrVIII, and XeVIII with the same core charges Z = 8 a.u., but with different core polarizations. The effect of the ionic core polarization is associated with the function Ψ₂. The population probabilities for n_A ≈ n_res are complemental to those obtained recently for n_A < n_res, and in sufficiently good agreement with available beam-foil experimental data. The pronounced resonances in the final population distributions are recognized only in the case of ArVIII ion and for the lower values of the solid work function (argon anomaly).     

The unusual variations of photoluminescence and afterglow properties in monoclinic ZrO2 by annealing

The raw ZrO₂ is annealed at 600–1550 °C for 6 h. It is found that the emission at 492 nm increases greatly when the annealing temperature is higher than 1200 °C and its afterglow shows a small improvement at 1200–1450 °C and a large enhancement after annealing at 1550 °C. The results that are obtained indicate that the impurity Ti⁴⁺ in ZrO₂ is efficiently reduced to Ti³⁺ when the temperature is higher than 1200 °C, and the increase of Ti³⁺ centers contributes to the large improvement of emission at 492 nm. The thermoluminescence shows that at least two types of traps with different depths (0.65 eV and 1.46 eV) corresponding to oxygen vacancies exist in monoclinic ZrO₂. After annealing at 1200–1450 °C, some new trap clusters related to oxygen vacancies and Ti³⁺ form and causes the small improvement of afterglow at 1200–1450 °C. The large improvement of afterglow after annealing at 1550 °C originates from the sharp increase of proper shallow traps (0.65 eV) in ZrO₂. Accordingly, we present the feasible interpretations and luminescence mechanisms of monoclinic ZrO₂ for our observations.     

The interfacial effect on ionic conduction of AgI–anatase TiO2 composites

AgI–anatase TiO₂ nanoparticle composites, (x)AgI–(1 ? x)anatase, with different porosities were fabricated over a wide range of 0–1 of AgI content. The electrical conductivity was measured at room temperature as function of AgI content (x) and porosity (p). The conductivity varies considerably with both x and p. In the vicinity of x = 0.4 and p = 0.31, the conductivity attains a maximum (2.5 × 10^? 3 S/cm). The conductivity is enhanced by three orders of magnitude in comparison with that of pristine AgI. The mechanism of the observed conductivity enhancement is discussed in the light of the scanning electron microscope images and X-ray diffraction patterns of the different (x)AgI–(1 ? x)anatase composites.     

Flame chemistry of tetrahydropyran as a model heteroatomic biofuel

The flame chemistry of tetrahydropyran (THP), a cyclic ether, has been examined using vacuum-ultraviolet (VUV)-photoionization molecular-beam mass spectrometry (PI-MBMS) and flame modeling, motivated by the need to understand and predict the combustion of oxygen-containing, biomass-derived fuels. Species identifications and mole-fraction profiles are presented for a fuel-rich (Φ = 1.75), laminar premixed THP–oxygen–argon flame at 2.66 kPa (20.0 Torr). Flame species with up to six heavy atoms have been detected. A detailed reaction set was developed for THP combustion that captures relevant features of the THP flame quite well, allowing analysis of the dominant kinetic pathways for THP combustion. Necessary rate coefficients and transport parameters were calculated or were estimated by analogies with a recent reaction set [Li et al., Combust. Flame 158 (2011) 2077–2089], and necessary thermochemical properties were computed using the CBS-QB3 method. Our results show that under the low-pressure conditions, THP destruction is dominated by H-abstraction, and the three resulting THP-yl radicals decompose primarily by β-scissions to two- and four-heavy-atom species that are generally destroyed by β-scission, abstraction, or oxidation.     

Laser ablation fast pulse discharge plasma spectroscopy analysis of Pb,Mg and Sn in soil

Laser ablation fast pulse discharge plasma spectroscopy (LA-FPDPS) technique is a recently developed atomic emission analytical technique that is analogous to dual pulse laser induced breakdown spectroscopy (DP-LIBS). LA-FPDPS, however, uses a periodical oscillating discharge plasma generation method on samples instead of the second laser beam in DP-LIBS. Here we describe the electric characteristics and its application to the analysis of Pb, Mg and Sn in soil. Due to the fast discharge process, the peak power deposition rate is up to 1.5 MW, although the discharge energy is relatively small. The main energy deposition process only last for ~ 4 μs. From the measured spectra, calibration curves for Pb, Mg and Sn in soil were derived and the limits of detection were 1.5 μg/g, 34 μg/g and 0.16 μg/g respectively.     

Correlation between phosphorus concentration and opto-electrical properties of doped a-Si:H films

Phosphorus doped hydrogenated amorphous silicon (a-Si:H) films were prepared by decomposition of silane using RF plasma glow discharge. Both DC dark conductivity measurements, and spectrophotometric optical measurements through the range 200–3000 nm were recorded for the prepared films. The DC conductivity activation energy E_a decreased from 0.8 eV for the undoped sample to 0.34 eV for the highest used doping value. The optical energy gap E_g decreased ranging from 1.66 eV to 1.60 eV. The refractive index n, the density of charge carriers N/m* and the plasma frequency ω_p showed an opposite behavior, i.e. an increase in value with doping. Fitting the dispersion values to Sellmeier equation led to the determination of the material natural frequency of oscillating particles. A correlation between the changes in these parameters with the doping has been attempted.