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Using a collisional radiative model coupled with optical emission spectroscopy (OES) of helium n  =  3 levels, the electron temperature (Te) of an atmospheric-pressure capacitively coupled radiofrequency (AP-CCRF) discharge in helium is determined with space and time resolution. When the AP-CCRF discharge is sustained in the mode, Te varies from 0.2 to 7.2 eV. In this case, high values of Te (>5 eV) occur only during a brief instant (<10 ns) in the high-voltage sheath. When the AP-CCRF discharge is sustained in the mode, Te varies from 0.3 to 0.4 eV during the complete cycle. The physical meaning of these electron temperatures are then analyzed by considering possible departure from the Maxwellian electron energy distribution function (EEDF). As a first approximation to non-Maxwellian distribution functions, a two-parameter EEDF was used to fit the OES data. This approach yields an overpopulation of high energy electrons with respect to the Maxwellian form in the mode and the opposite trend in the mode. [ABSTRACT FROM AUTHOR]

Diffuse dielectric barrier discharges are generated over a very wide range of frequencies. According to the targeted frequency, the glow, Townsend-like, hybrid, Ω and RF-α modes are sustained. In this paper, the electrical characterization of the discharge cell together with an electrical model are used to estimate the electron density from current and voltage measurements for excitation frequencies ranging from 50 kHz to 15 MHz. The electron density is found to vary from 1014 to 1017 m−3 over this frequency range. In addition, a collisional-radiative model coupled with optical emission spectroscopy is used to evaluate the electron temperature (assuming Maxwellian electron energy distribution function) in the same conditions. The time and space-averaged electron temperature is found to be about 0.3 eV in both the low-frequency and high-frequency ranges. However, in the medium-frequency range, it reaches almost twice this value as the discharge is in the hybrid mode. The hybrid mode is similar to the atmospheric-pressure glow discharge usually observed in helium DBDs at low frequency with the major difference being that the plasma is continuously sustained and is characterized by a higher power density. [ABSTRACT FROM AUTHOR]

A new spatially averaged time-dependent collisional-radiative model for helium plasmas, coupled to the electron Boltzmann equation (EBE), has been developed. Its main novelties are: (1) full time dependence for both the multi-species kinetics and the EBE. It is shown that this is necessary to correctly simulate discharges where the parameters vary on nanoseconds-microsecond timescales. (2) All electron processes are accounted for accurately. In particular, for the various ionization and recombination processes, free electrons are added or removed at the appropriate energy, with the appropriate interpolation on the energy grid. (3) The energy dependence of the electron loss by ambipolar diffusion is taken into account approximately. (4) All of the processes which are known to be important in helium discharges for pressure Torr are included, and 42 energy levels up to n = 6, where n is the main quantum number, are taken into account. Atomic and molecular ions, as well as excimers, are also included. (5) The gas temperature is calculated self-consistently. The model is validated through comparisons with known numerical steady-state results of Santos et al (2014 J. Phys. D.47 265201) which they compared to their experimental results, and good agreement is obtained for their measured quantities. It is then applied to post-discharge decay cases with very short power decay times. The time evolution of the population densities and reaction rates are analyzed in detail with emphasis on the observed large increase of the metastable density. [ABSTRACT FROM AUTHOR]

Carbon dust particles with radius of a few hundreds of nanometers are formed in a steady-state plasma produced by an electromagnetic surface wave at 200 MHz in very low-pressure conditions. The influence of an applied magnetic field is evidenced by ex situ methods (scanning and transmission electron microscopy, Raman spectroscopy). The observed spherical dust particles are formed of aggregates of graphite nanocrystals embedded in amorphous carbon shells. In addition, the size of the dust particles increases with the magnetic field intensity. Growth occurs as the particles are confined near the sheath edge and their confinement is improved by applying a magnetic field as the corresponding electric field increases in this region. As a consequence, the average dust particle radius is directly related to the magnetic field intensity. [ABSTRACT FROM AUTHOR]

Recent studies have shown that tuning a dielectric barrier discharge (DBD) in the medium-frequency range (MF: from 0.3 to 3 MHz) allows a low-power and a high-power mode to be sustained. In the present article the effect of the driving frequency on a DBD is studied from the low-frequency range (LF: from 30 to 300 kHz) to the high-frequency range (HF: from 3 to 30 MHz). This is achieved using fast imaging together with electrical and spectroscopic diagnostics. At every frequency, a diffuse discharge is sustained. It is observed that at 25 kHz the discharge is an atmospheric-pressure glow discharge (APGD) while at 15 MHz the discharge behaves as a capacitive discharge in the RF-α mode. The usual LF APGD behavior is observed up to 100 kHz. Above 200 kHz, the positive column remains during the whole cycle so that the hybrid mode is sustained. At 5 MHz, the hybrid mode finally turns into the RF-α mode. In addition to the LF APGD, RF-α and hybrid modes obtained when the applied voltage is significantly higher than the ignition value, two other modes can be reached at low applied voltage. A Townsend-like mode is achieved from 50 to 100 kHz while in the medium-frequency range, the Ω mode is sustained. Moreover, only from 1.0 to 2.7 MHz there is a large hysteresis occurring when the discharge transits back and forth from the Ω to the hybrid mode. It is also found that when the frequency increases from 25 kHz to 15 MHz, the rms current increases over two orders of magnitudes while the rms voltage decreases by about 60%. The gas temperature estimated from N2 rotational spectra is always close to room temperature but the discharge is more energy efficient (in the HF range) as a lower fraction of energy turns into gas heating. [ABSTRACT FROM AUTHOR]

Dust particles formation was investigated in magnetically confined low-pressure plasma produced in argon-acetylene mixtures. The plasma characteristics were measured in order to identify the species involved in the dust particles formation. Their dependence on the operating conditions including magnetic field intensity, acetylene fraction in the gas mixture and operating pressure was examined. In contrast with noble gases, in the presence of acetylene, the electron temperature increases with the magnetic field intensity, indicating additional charged particles losses in the plasma. Indeed, in these conditions, larger hydrocarbon ions are produced leading to the formation of dust particles in the plasma volume. The observed dependence of positive ion mass distribution and density and relative negative ion density on the operating parameters suggests that the dust particles are formed through different pathways, where negative and positive ions are both involved in the nucleation. [ABSTRACT FROM AUTHOR]

In this paper, we investigate DBDs in the medium frequency range (MF, 0.3–3 MHz). More precisely, for a 2 inter-dielectric gap in helium at atmospheric pressure, the frequency is varied from 1.0 to 2.7 MHz. The generated discharge shows similarities with both the low-frequency atmospheric-pressure glow discharge (APGD) and the atmospheric pressure capacitively coupled radio-frequency (CCRF) discharge. In the frequency range under investigation, two diffuse discharge modes can be observed depending on the voltage applied between the electrodes. At low applied voltage, the discharge emissions are barely visible and are concentrated in the center of the gas gap similarly to CCRF discharges in the mode where the electron density is concentrated in the bulk. Ohmic heating is the main power transfer mechanism. At higher applied voltage, the discharge emissions are 10 times more intense and are closer to the dielectric surfaces similarly to the more common radio-frequency α mode. These two discharge modes can be observed in the same experimental conditions with the amplitude of the applied voltage as sole control parameter. The gas temperature obtained from N2 impurities rotational spectrum increases from room temperature to about 500 K while the power density rises from 10−1 to 101 W cm−3 when the applied voltage is increased. In addition, when the discharge transits back and forth from the to the α mode, a hysteresis is observed. The transition from the to the α mode occurs abruptly with a large RMS current increase while the transition from the α to the mode is rather smooth with no significant discontinuity in the RMS current. [ABSTRACT FROM AUTHOR]

Optical emission spectroscopy (OES) measurements coupled with a collisional-radiative model were used to characterize a plane-to-plane dielectric barrier discharge at atmospheric pressure operated in nominally pure helium. The model predicts the population densities for the n  =  3 levels of He excited by electron impact processes from either ground or metastable states and takes into account excitation transfer processes between He n  =  3 levels as well as all relevant radiative decays and quenching reactions. Time-resolved OES measurements indicate that line ratios from He n  =  3 triplet states (for example, 587.5 nm-to-706.5 nm) and singlet states (for example, 667.8 nm-to-728.1 nm) first sharply rise as the discharge ignites and then slowly decrease as it extinguishes. Assuming that n  =  3 levels are first populated only by electron impact on ground state He atoms and then only by electron impact on metastable He atoms as the discharge current and thus the metastable number density rise, triplet and singlet line ratios predicted by the model become in each opposite case solely dependent on the electron temperature Te (assuming Maxwellian electron energy distribution function). The values of Te deduced from the analysis of both ratios were relatively high early in the discharge cycle (around 1.0–1.4 eV) and then much lower near discharge extinction (around 0.15 eV). For analysis of time-integrated (or cycle-averaged) OES measurements, the electron temperatures were closer to the 0.15 eV values near the end of the discharge cycle, in good agreement with the values expected from theoretical predictions in the positive columns of He glow discharges at atmospheric pressure. [ABSTRACT FROM AUTHOR]

In this work, we demonstrate a full process for fabricating high aspect ratio diffraction optics for extreme ultraviolet lithography. The transmissive optics consists in nanometer scale tungsten patterns standing on flat, ultrathin (100 nm) and highly transparent (>85% at 13.5 nm) silicon membranes (diameter of 1 mm). These tungsten patterns were achieved using an innovative pseudo-Bosch etching process based on an inductively coupled plasma ignited in a mixture of SF6 and C4F8. Circular ultra-thin Si membranes were fabricated through a state-of-the-art method using direct-bonding with thermal difference. The silicon membranes were sputter-coated with a few hundred nanometers (100–300 nm) of stress-controlled tungsten and a very thin layer of chromium. Nanoscale features were written in a thin resist layer by electron beam lithography and transferred onto tungsten by plasma etching of both the chromium hard mask and the tungsten layer. This etching process results in highly anisotropic tungsten features at room temperature. The homogeneity and the aspect ratio of the advanced pattern transfer on the membranes were characterized with scanning electron microscopy after focus ion beam milling. An aspect ratio of about 6 for 35 nm size pattern is successfully obtained on a 1 mm diameter 100 nm thick Si membrane. The whole fabrication process is fully compatible with standard industrial semiconductor technology. [ABSTRACT FROM AUTHOR]

Phase competition in transition metal oxides has attracted remarkable interest for fundamental aspects and technological applications. Here, we report a concurrent study of the phase transitions in undoped and Cr-doped VO[Formula: see text] thin films. The structural, morphological and electrical properties of our films are examined and the microstructural effect on the metal-insulator transition (MIT) are highlighted. We further present a distinctive approach for analyzing the Raman data of undoped and Cr-doped VO[Formula: see text] thin films as a function of temperature, which are quantitatively correlated to the electrical measurements of VO[Formula: see text] films to give an insight into the coupling between the structural phase transition (SPT) and the MIT. These data are also combined with reported EXAFS measurements and a connection between the Raman intensities and the mean Debye-Waller factors [Formula: see text] is established. We found that the temperature dependence of the [Formula: see text] as calculated from the Raman intensity retraces the temperature profile of the [Formula: see text] as obtained from the EXAFS data analysis. Our findings provide an evidence on the critical role of the thermal vibrational disorder in the VO[Formula: see text] phase transitions. Our study demonstrates that correlating Raman data with EXAFS analysis, the lattice and electronic structural dynamics can be probed.

Due to the practical applications of polymer solar cells (PSCs), their stability recently has received increasing attention. Herein, a new strategy was developed to largely enhance the long-term and thermal stability of PSCs in air with a relatively high humidity of 50-60% without any encapsulation. In this strategy, semiconductor PbS/CdS core/shell quantum dots (QDs) were incorporated into the photoactive blend of poly(3-hexylthiophene) (P3HT) and phenyl-C 61 -butyric acid methyl ester (PCBM). By replacing the initial ligands of oleic acid with halide ligands on the surface of PbS/CdS QDs via solution-phase ligand exchange, we were able to form unusual, continuous QD networks in the film of P3HT:PCBM, which effectively stabilized the photoactive layer. Air-processed PSCs based on the stabilized P3HT:PCBM film showed excellent long-term stability under high humidity, providing over 3% of power conversion efficiency (PCE) simultaneously. Around 91% of pristine PCE was retained after 30 days storage in high-humidity air without encapsulation. This constitutes a remarkable improvement compared to ∼53% retained PCE for the QD-free devices, which can be ascribed to the efficient suppression of both PCBM aggregation and oxidation of the thiophene ring in P3HT, thanks to the formation of robust QD networks. Furthermore, the presence of QD networks was able to enhance the stability of the P3HT:PCBM film against thermal stress/oxidation under high-humidity environment (50-60%) as well. The device kept 60% of pristine PCE after thermal treatment for 12 h at 85 °C in air, which is more than twice higher than that for the QD-free device. To the best of our knowledge, the work represents the first unambiguous demonstration of the formation of QD networks in the photoactive layer and of their important contribution to the stability of PSCs. This strategy is highly promising for other fullerene-based PSCs and opens a new avenue toward achieving PSCs with high PCE and excellent stability.

Samarium nickelate (SmNiO 3 ) thin films were successfully synthesized on LaAlO 3 and SrTiO 3 substrates using pulsed-laser deposition. The Mott metal-insulator (MI) transition of the thin films is sensitive to epitaxial strain and strain relaxation. Once the strain changes from compressive to tensile, the transition temperature of the SmNiO 3 samples shifts to slightly higher values. The optical conductivity reveals the strong dependence of the Drude spectral weight on the strain relaxation. Actually, compressive strain broadens the bandwidth. In contrast, tensile strain causes the effective number of free carriers to reduce which is consistent with the d-band narrowing.

In this work, optical properties of epitaxial Ca x Ba 1-x Nb 2 O 6 , CBN (x = 0.28) thin film based waveguides are studied at 1550 nm optical communications wavelength. CBN thin films are deposited epitaxially on MgO substrates using Pulsed Laser Deposition and characterized by prism coupling to extract the refractive index and propagation loss. It is shown that the 2 µm-thick epitaxial CBN thin films have a refractive index close to the bulk form and the CBN planar waveguides have a propagation loss of 4.3 ± 0.5 dB/cm. 1 cm-long rib waveguide structures were fabricated using a high density plasma etching. Their propagation losses were measured by the cutback method at 8.4 ± 0.6 dB/cm.

In this work, we demonstrate a full process for fabricating high aspect ratio diffraction optics for extreme ultraviolet lithography. The transmissive optics consists in nanometer scale tungsten patterns standing on flat, ultrathin (100 nm) and highly transparent (>85% at 13.5 nm) silicon membranes (diameter of 1 mm). These tungsten patterns were achieved using an innovative pseudo-Bosch etching process based on an inductively coupled plasma ignited in a mixture of SF6 and C4F8. Circular ultra-thin Si membranes were fabricated through a state-of-the-art method using direct-bonding with thermal difference. The silicon membranes were sputter-coated with a few hundred nanometers (100-300 nm) of stress-controlled tungsten and a very thin layer of chromium. Nanoscale features were written in a thin resist layer by electron beam lithography and transferred onto tungsten by plasma etching of both the chromium hard mask and the tungsten layer. This etching process results in highly anisotropic tungsten features at room temperature. The homogeneity and the aspect ratio of the advanced pattern transfer on the membranes were characterized with scanning electron microscopy after focus ion beam milling. An aspect ratio of about 6 for 35 nm size pattern is successfully obtained on a 1 mm diameter 100 nm thick Si membrane. The whole fabrication process is fully compatible with standard industrial semiconductor technology.

Nitrifying wastewater treatment plants (WWTPs) are more efficient than non-nitrifying WWTPs to remove several micropollutants such as pharmaceuticals and pesticides. This may be related to the activity of nitrifying organisms, such as ammonia-oxidizing bacteria (AOBs), which could possibly co-metabolically oxidize micropollutants with their ammonia monooxygenase (AMO). The role of AOBs in micropollutant removal was investigated with aerobic granular sludge (AGS), a promising technology for municipal WWTPs. Two identical laboratory-scale AGS sequencing batch reactors (AGS-SBRs) were operated with or without nitrification (inhibition of AMOs) to assess their potential for micropollutant removal. Of the 36 micropollutants studied at 1 μg l(-1) in synthetic wastewater, nine were over 80% removed, but 17 were eliminated by less than 20%. Five substances (bisphenol A, naproxen, irgarol, terbutryn and iohexol) were removed better in the reactor with nitrification, probably due to co-oxidation catalysed by AMOs. However, for the removal of all other micropollutants, AOBs did not seem to play a significant role. Many compounds were better removed in aerobic condition, suggesting that aerobic heterotrophic organisms were involved in the degradation. As the AGS-SBRs did not favour the growth of such organisms, their potential for micropollutant removal appeared to be lower than that of conventional nitrifying WWTPs.

An innovative method to fabricate large area (up to several squared millimeters) ultrathin (100 nm) monocrystalline silicon (Si) membranes is described. This process is based on the direct bonding of a silicon-on-insulator wafer with a preperforated silicon wafer. The stress generated by the thermal difference applied during the bonding process is exploited to produce buckling free silicon nanomembranes of large areas. The thermal differences required to achieve these membranes (≥1 mm(2)) are estimated by analytical calculations. An experimental study of the stress achievable by direct bonding through two specific surface preparations (hydrophobic or hydrophilic) is reported. Buckling free silicon nanomembranes secured on a 2 × 2 cm(2) frame with lateral dimensions up to 5 × 5 mm(2) are successfully fabricated using the optimized direct bonding process. The stress estimated by theoretical analysis is confirmed by Raman measurements, while the flatness of the nanomembranes is demonstrated by optical interferometry. The successful fabrications of high resolution (50 nm half pitch) tungsten gratings on the silicon nanomembranes and of focused ion beam milling nanostructures show the promising potential of the Si membranes for X-ray optics and for the emerging nanosensor market.

Relatively high concentrations of micropollutants in municipal wastewater treatment plant (WWTP) effluents underscore the necessity to develop additional treatment steps prior to discharge of treated wastewater. Microorganisms that produce unspecific oxidative enzymes such as laccases are a potential means to improve biodegradation of these compounds. Four strains of the bacterial genus Streptomyces (S. cyaneus, S. ipomoea, S. griseus and S. psammoticus) and the white-rot fungus Trametes versicolor were studied for their ability to produce active extracellular laccase in biologically treated wastewater with different carbon sources. Among the Streptomyces strains evaluated, only S. cyaneus produced extracellular laccase with sufficient activity to envisage its potential use in WWTPs. Laccase activity produced by T. versicolor was more than 20 times greater, the highest activity being observed with ash branches as the sole carbon source. The laccase preparation of S. cyaneus (abbreviated LSc) and commercial laccase from T. versicolor (LTv) were further compared in terms of their activity at different pH and temperatures, their stability, their substrate range, and their micropollutant oxidation efficiency. LSc and LTv showed highest activities under acidic conditions (around pH 3 to 5), but LTv was active over wider pH and temperature ranges than LSc, especially at near-neutral pH and between 10 and 25°C (typical conditions found in WWTPs). LTv was also less affected by pH inactivation. Both laccase preparations oxidized the three micropollutants tested, bisphenol A, diclofenac and mefenamic acid, with faster degradation kinetics observed for LTv. Overall, T. versicolor appeared to be the better candidate to remove micropollutants from wastewater in a dedicated post-treatment step.

Many organic compounds present at low concentrations in municipal wastewater, such as various pharmaceuticals and biocides, are recalcitrant in conventional wastewater treatment plants (WWTPs). To improve their biodegradation, oxidoreductase enzymes such as laccases were tested. The goal was to find optimal conditions for the transformation of two anti-inflammatory pharmaceuticals (diclofenac (DFC) and mefenamic acid (MFA)), one biocide (triclosan (TCN)) and one plastic additive (bisphenol A (BPA)) by Trametes versicolor laccase. Experiments were conducted in spiked solutions at different pH values (from 3 to 9), enzyme concentrations (70-1400 Ul(-1)), reaction times (0-26 hours) and temperatures (10, 25 and 40°C) following a Doehlert experimental design. A semi-empirical model was developed to understand better the combined effects of the four factors and to determine optimal values. This model was able to fit well the experimental data (R(2)>0.97) and showed good predictive ability. All four factors had a significant effect on the micropollutant oxidation with the greatest influence shown by pH. Results for single compounds were different from those obtained for mixtures of micropollutants. For instance, DFC transformation occurred at much higher rates in mixtures under alkaline conditions. Optimal conditions were compound-dependent, but were found to be between pH 4.5 to 6.5 and between 25°C to more than 40°C. A laccase concentration of 730 Ul(-1) was sufficient to obtain a high removal rate (>90%) of the four individual compounds (range of times: 40 min to 5 hours), showing the potential of laccases to improve biodegradation of environmentally persistent compounds., (Copyright © 2013 Elsevier B.V. All rights reserved.)

Many organic micropollutants present in wastewater, such as pharmaceuticals and pesticides, are poorly removed in conventional wastewater treatment plants (WWTPs). To reduce the release of these substances into the aquatic environment, advanced wastewater treatments are necessary. In this context, two large-scale pilot advanced treatments were tested in parallel over more than one year at the municipal WWTP of Lausanne, Switzerland. The treatments were: i) oxidation by ozone followed by sand filtration (SF) and ii) powdered activated carbon (PAC) adsorption followed by either ultrafiltration (UF) or sand filtration. More than 70 potentially problematic substances (pharmaceuticals, pesticides, endocrine disruptors, drug metabolites and other common chemicals) were regularly measured at different stages of treatment. Additionally, several ecotoxicological tests such as the Yeast Estrogen Screen, a combined algae bioassay and a fish early life stage test were performed to evaluate effluent toxicity. Both treatments significantly improved the effluent quality. Micropollutants were removed on average over 80% compared with raw wastewater, with an average ozone dose of 5.7 mg O3 l(-1) or a PAC dose between 10 and 20 mg l(-1). Depending on the chemical properties of the substances (presence of electron-rich moieties, charge and hydrophobicity), either ozone or PAC performed better. Both advanced treatments led to a clear reduction in toxicity of the effluents, with PAC-UF performing slightly better overall. As both treatments had, on average, relatively similar efficiency, further criteria relevant to their implementation were considered, including local constraints (e.g., safety, sludge disposal, disinfection), operational feasibility and cost. For sensitive receiving waters (drinking water resources or recreational waters), the PAC-UF treatment, despite its current higher cost, was considered to be the most suitable option, enabling good removal of most micropollutants and macropollutants without forming problematic by-products, the strongest decrease in toxicity and a total disinfection of the effluent., (Copyright © 2013 Elsevier B.V. All rights reserved.)

Pharmaceuticals constitute an important environmental issue for receiving waters. A holistic approach, taking into consideration the sources of these compounds (hospitals, domestic use), discharges (wastewater effluent, combined sewer overflows) and related risks to the environment, is therefore needed to develop the best protection strategy. The substance flow analysis (SFA) approach, applied, for example, to the city of Lausanne, Switzerland, is an ideal tool to tackle these issues. Four substances were considered: one antibiotic (ciprofloxacin), an analgesic (diclofenac), and two anti-epileptics (carbamazepine and gabapentin). Consumption data for the main hospital of the city (916 beds) and for the population were available. Micropollutant concentrations were measured at different points of the system: wastewater inlet and outlet (WWTP), combined sewer overflows (CSO) and in the receiving waters (Vidy Bay, Lake Geneva). Measured and predicted concentrations were in agreement, except for diclofenac, for which analytical uncertainties were expected. Seven different scenarios were considered (supplementary treatment at the WWTP, at the hospital or at both places, etc.). Based on the results obtained, the supplementary treatment at the WWTP decreases the load of pharmaceuticals reaching surface water by a factor between 2 and 27, depending on the compound and on the technique. The treatment at the hospitals only influences the amount of ciprofloxacin reaching the environment and decreases the release by one third. The contribution of CSO to surface water pollution is low compared to that of the WWTP for the selected compounds. Regarding the risk for the receiving waters, ciprofloxacin was found to be the most problematic compound, with a risk quotient far above 1. In this particular case, a treatment at the WWTP is not sufficient to reduce the risk, and additional measures at the CSO or at the hospital should be considered. SFA is an ideal tool for developing the best strategy for pharmaceutical elimination, but its application depends on data availability and local conditions., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

Sediment represents an important compartment in surface waters. It constitutes a habitat or spawning site for many organisms and is an essential trophic resource for higher level organisms. It can be impacted by anthropogenic activities, particularly through urban wet-weather discharges like stormwater and combined sewer overflows. An approach was presented for assessing the risks caused by urban wet-weather discharges to the sediment compartment based on total suspended solids (TSS). TSS is routinely measured in field surveys and can be considered as a tracer for urban wet-weather contamination. Three assessment endpoints linked with TSS were proposed: a) siltation of the riverbed, b) oxygen demand due to organic matter degradation and c) accumulation of ecotoxic contaminants on the riverbed (heavy metals, PAHs). These criteria were translated in terms of the maximal TSS accumulation load and exposure time (percentage of time exceeding the accumulation criteria) to account for sediment accumulation dynamics and resuspension in streams impacted by urban wet-weather discharges. These assessment endpoints were implemented in a stochastic model that calculates TSS behavior in receiving waters and allows therefore an assessment of potential impacts. The approach was applied to three Swiss case studies. For each, good agreement was found between the risk predictions and the field measurements confirming the reliability of the approach., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

The aim of this work was to evaluate low-cost and easy-to-operate engineering solutions that can be added as a polishing step to small wastewater treatment plants to reduce the micropollutant load to water bodies. The proposed design combines a sand filter/constructed wetland with additional and more advanced treatment technologies (UV degradation, enhanced adsorption to the solid phase, e.g., an engineered substrate) to increase the elimination of recalcitrant compounds. The removal of five micropollutants with different physico-chemical characteristics (three pharmaceuticals: diclofenac, carbamazepine, sulfamethoxazole, one pesticide: mecoprop, and one corrosion inhibitor: benzotriazole) was studied to evaluate the feasibility of the proposed system. Separate batch experiments were conducted to assess the removal efficiency of UV degradation and adsorption. The efficiency of each individual process was substance-specific. No process was effective on all the compounds tested, although elimination rates over 80% using light expanded clay aggregate (an engineered material) were observed. A laboratory-scale flow-through setup was used to evaluate interactions when removal processes were combined. Four of the studied compounds were partially eliminated, with poor removal of the fifth (benzotriazole). The energy requirements for a field-scale installation were estimated to be the same order of magnitude as those of ozonation and powdered activated carbon treatments.

Spatially resolved trace rare gases optical emission spectroscopy was used to analyze the electron energy-distribution function (EEDF) in low-pressure argon plasma columns sustained by surface waves. At frequencies >1 GHz, in the microwave-sustained region, the EEDF departs from a Maxwellian, characterized by a depletion of low-energy electrons and a high-energy tail, whereas in the field-free zone, the EEDF is Maxwellian. Abnormal behavior of the EEDF results from the acceleration of low-energy electrons due to the conversion of surface waves into volume plasmons at the resonance point where the plasma frequency equals the wave frequency and their absorption by either collisional or Landau damping.

The dependence on laser fluence and laser pulse duration of size, size distribution and concentration of gold nanoparticles synthesized by laser ablation in liquid media was investigated. It was demonstrated that increasing laser energy from 1 to 5 mJ/pulse enhances the ablation rate by a factor of 100. The behavior of the ablation rate, hence of the nanoparticle concentration, as a function of pulse duration (varied from 40 fs to 200 ps) was found to strongly differ from that in air, which can be explained by photoionization and important losses of laser energy in the femtosecond regime. The optimal pulse duration for maximum ablation rate in liquid media was found to be equal to 2 ps.

Negative capacitance (NC) in a planar W-doped VO 2 micro-switch was observed at room temperature in the low-frequency range 1 kHz-10 MHz. The capacitance changed from positive to negative values as the W-doped VO 2 active layer switched from semiconducting to metallic state under applied voltage. In addition, a capacitance-voltage hysteresis was observed as the applied voltage was cycled from -35 to 35 V. These observations suggest that NC results from the increase of the electrically induced conductivity in the active layer. This NC phenomenon could be exploited in advanced multifunctional devices including ultrafast switches, field-effect transistors and memcapacitive systems.

In this work, the assumption of local thermodynamic equilibrium (LTE) for a laser-induced plasma in ambient air is examined experimentally using two different laser systems, namely an infrared short-pulse Ti : Sapphire laser and an ultraviolet long-pulse XeCl excimer laser. The LTE assumption is investigated by examining the plasma produced at a laser fluence of 10 J/cm(2) from aluminum targets containing iron and magnesium impurities. The excitation temperature is deduced from Boltzmann diagrams built from a large number of spatially integrated neutral iron lines distributed from 3.21 to 6.56 eV. It is shown that at any time after the end of the laser pulse, the neutral excited states are in excellent Boltzmann equilibrium. Detailed investigation of Boltzmann equilibrium further validates previous temperature measurements using less accurate diagrams. However, observations of ion lines provide some evidence that the ionized species do not obey Saha equilibrium, thereby indicating departure from LTE. This could be explained by the fact that the plasma cannot be considered as stationary for these species.

The ablated depth and volume per laser pulse from an aluminum target were measured for pulse durations that ranged from 80 fs to 270 ps at an average fluence of approximately 100 J/cm2 and a wavelength of 0.8 microm. The ablated volume showed a flat maximum for subpicosecond pulses and a minimum for approximately 6 ps. The crater diameters were rather constant up to pulse durations of approximately 6 ps and increased for larger pulse durations. As a result, the ablated depth also showed a plateau for subpicosecond pulses but decreased monotonically with pulse duration. A physical interpretation of these results and their consequences for laser applications are discussed.

Quantitative analysis of aluminum and copper alloys by means of laser-induced plasma spectroscopy (LIPS) has been investigated for three representative laser pulse durations (80 fs, 2 ps, and 270 ps). The experiments were carried out in air at atmospheric pressure with a constant energy density of 20 J/cm2. Because the decay rate of the spectral emission depends on the laser pulse duration, the optimum detection requires an optimization of the temporal gating acquisition parameters. LIPS calibration (sensitivity and nonlinearity) and the limit of detection (LOD) are discussed in detail. While the LOD of minor elements embedded in alloy samples obtained by sub-picosecond or sub-nanosecond laser pulses are both time and element dependent, provided an appropriate temporal window is chosen, the optimum LODs (several parts per million (ppm)) prove to be independent of the laser pulse duration. Finally, it is found that for elements such as those detected here, gated LIPS spectra using picosecond or sub-picosecond laser pulses provide much better LOD values than non-gated spectra.

Laser ablation of an aluminum target as a function of the pulse duration, for fluences up to 30 J/cm(2) and a wavelength of 0.8 microm, is investigated by means of a fluid code. For a given fluence, the ablation depth shows a minimum for a pulse duration of approximately 10 ps between a maximum obtained for pulses shorter than approximately 1 ps and a lower maximum obtained for pulses in the nanosecond range, in qualitative agreement with published experimental results. The decrease in ablation depth with increase in pulse duration observed between 1 and 10 ps results from the reduced temperature rise near the surface due to increased inward heat transport. The increase in the ablation depth above approximately 10 ps is due to the increase in electron density gradient length while the laser pulse intensity is close to maximum, which thus enables the plasma to absorb more of the laser pulse energy for increased ablation.