Abstract: In this work, a hybrid model is used to investigate the effect of different gas ratios on the Si etching and polymer film deposition characteristics in an Ar/CF4 inductively coupled plasma. The influence of the surface processes on the bulk plasma properties is studied, and also the spatial characteristics of important gas phase and etched species. The densities of F and CF2 decrease when the surface module is included in the simulations, due to the species consumption caused by etching and polymer deposition. The influence of the surface processes on the bulk plasma depends on the Ar/CF4 gas ratio. The deposited polymer becomes thicker at high CF4 content because of more abundant CFx radicals. As a result of the competition between the polymer thickness and the F flux, the etch rate first increases and then decreases upon increasing the CF4 content. The electron properties, more specifically the electron density profile, affect the Si etch characteristics substantially by determining the radical density and flux profiles. In fact, the radial profile of the etch rate is more uniform at low CF4 content since the electron density has a smooth distribution. At high CF4 content, the etch rate is less uniform with a minimum halfway along the wafer radius, because the electron density distribution is more localized. Therefore, our calculations predict that it is better to work at relatively high Ar/CF4 gas ratios, in order to obtain high etch rate and good profile uniformity for etch applications. This, in fact, corresponds to the typical experimental etch conditions in Ar/CF4 gas mixtures as found in the literature, where Ar is typically present at a much higher concentration than CF4.

Abstract: Plasma medicine has been claimed to provide a novel route to heal wounds and regenerate skin, although very little is currently known about the elementary processes taking place. We carried out a series of ReaxFF-based reactive molecular dynamics simulations to investigate the interaction of O and OH radicals with lipids, more specifically with α-linolenic acid as a model for the free fatty acids present in the upper skin layer. Our calculations predict that the O and OH radicals most typically abstract a H atom from the fatty acids, which can lead to the formation of a conjugated double bond, but also to the incorporation of alcohol or aldehyde groups, thereby increasing the hydrophilic character of the fatty acids and changing the general lipid composition of the skin. Within the limitations of the investigated model, no formation of possibly toxic products was observed.

Abstract: A theoretical study of ultrashort laser-induced electron emission from a negatively biased metallic cathode has been performed. Classical as well as tunneling electron emission mechanisms are considered. It was found that electron emission is governed by an interplay of processes inside as well as above the cathode. A hybrid model is proposed, where the electron distribution within the target is retrieved from Boltzmann scattering integrals, while the charge distribution above it is studied by a Particle-In-Cell simulation. The results indicate that non-equilibrium effects determine the initial emission process, whereas the space charge above the target suppresses the effectively emitted charge.

Abstract: Despite significant progress in single walled carbon nanotube (SWCNT) production by plasma enhanced chemical vapor deposition (PECVD), the growth mechanism in this method is not clearly understood. We employ reactive molecular dynamics simulations to investigate how plasma-based deposition allows growth at low temperature. We first investigate the SWCNT growth mechanism at low and high temperatures under conditions similar to thermal CVD and PECVD. We then show how ion bombardment during the nucleation stage increases the carbon solubility in the catalyst at low temperature. Finally, we demonstrate how moderate energy ions sputter amorphous carbon allowing for SWCNT growth at 500 K. (C) 2013 Elsevier B. V. All rights reserved.

Abstract: The unique plasma-specific features and physical phenomena in the organization of nanoscale soild-state systems in a broad range of elemental composition, structure, and dimensionality are critically reviewed. These effects lead to the possibility to localize and control energy and matter at nanoscales and to produce self-organized nano-solids with highly unusual and superior properties. A unifying conceptual framework based on the control of production, transport, and self-organization of precursor species is introduced and a variety of plasma-specific non-equilibrium and kinetics-driven phenomena across the many temporal and spatial scales is explained. When the plasma is localized to micrometer and nanometer dimensions, new emergent phenomena arise. The examples range from semiconducting quantum dots and nanowires, chirality control of single-walled carbon nanotubes, ultra-fine manipulation of graphenes, nano-diamond, and organic matter to nano-plasma effects and nano-plasmas of different states of matter.

Abstract: The present study focuses on the role of mass removal mechanisms in ns-laser ablation. A copper sample is placed in argon, initially set at standard pressure and temperature. Calculations are performed for a 6 ns laser pulse with a wavelength of 532 nm and laser fluences up to 10 J/cm2. The transient behavior in and above the copper target is described by a hydrodynamic model. Transmission profiles and ablation depths are compared with experimental results and similar trends are found. Our calculations reveal an interesting self-inhibiting mechanism: volumetric mass removal in the supercritical region triggers plasma shielding and therefore stops proceeding. This self-limiting process indicates that volumetric mass removal does not necessarily result in large ablation depths.

Abstract: In recent years, the potential use of hydrogen as a clean energy source has gained considerable attention. Especially H2 formation by Ni-catalyzed reforming of methane at elevated temperatures is an attractive process. However, a more fundamental knowledge at the atomic level is needed for a full comprehension of the reactions at the catalyst surface. In this contribution, we therefore investigate the H2 formation after CHx impacts on a Ni(1 1 1) surface in the temperature range 4001600 K, by means of reactive molecular dynamics (MD) simulations using the ReaxFF potential. While some H2 formation is already observed at the lower temperatures, substantial H2 formation is only obtained at elevated temperatures of 1400 K and above. At 1600 K, the H2 molecules are even the most frequently formed species. In direct correlation with the increasing dehydrogenation at elevated temperatures, an increased surface-to-subsurface C-diffusivity is observed as well. This study highlights the major importance of the temperature on the H2 formation.

Abstract: CO2 exchange between terrestrial ecosystems and the atmosphere is key to understanding the feedbacks between climate change and the land surface. In regions with carbonaceous parent material, CO2 exchange patterns occur that cannot be explained by biological processes, such as disproportionate outgassing during the daytime or night-time CO2 uptake during periods when all vegetation is senescent. Neither of these phenomena can be attributed to carbonate weathering reactions, since their CO2 exchange rates are too small. Soil ventilation induced by high atmospheric turbulence is found to explain atypical CO2 exchange between carbonaceous systems and the atmosphere. However, by strongly altering subsurface CO2 concentrations, ventilation can be expected to influence carbonate weathering rates. By imposing ventilation-driven CO2 outgassing in a carbonate weathering model, we show here that carbonate geochemistry is accelerated and does play a surprisingly large role in the observed CO2 exchange pattern of a semi-arid ecosystem. We found that by rapidly depleting soil CO2 during the daytime, ventilation disturbs soil carbonate equilibria and therefore strongly magnifies daytime carbonate precipitation and associated CO2 production. At night, ventilation ceases and the depleted CO2 concentrations increase steadily. Dissolution of carbonate is now enhanced, which consumes CO2 and largely compensates for the enhanced daytime carbonate precipitation. This is why only a relatively small effect on global carbonate weathering rates is to be expected. On the short term, however, ventilation has a drastic effect on synoptic carbonate weathering rates, resulting in a pronounced diel pattern that exacerbates the non-biological behavior of soil-atmosphere CO2 exchanges in dry regions with carbonate soils.

Abstract: Theranostic polymeric nanocarriers loaded with anticancer drug Taxol and superparamagnetic iron oxide nanocrystals have been developed for possible magnetic resonance imaging (MRI) use and cancer therapy. Multifunctional nanocarriers with a coreshell structure have been prepared by coating superparamagnetic Fe3O4 nanoparticles with block copolymer of poly(ethylene glycol)-b-poly(propylene succinate) with variable molecular weights of the hydrophobic block poly(prolylene succinate). The multifunctional polymer nano-vehicles were prepared using a nanoprecipitation method. Scanning transmission electron microscopy revealed the encapsulation of magnetic nanoparticles inside the polymeric matrix. Energy dispersive X-ray spectroscopy and electron energy loss spectroscopy mapping allowed us to determine the presence of the different material ingredients in a quantitative way. The diameter of the nanoparticles is below 250 nm yielding satisfactory encapsulation efficiency. The nanoparticles exhibit a biphasic drug release pattern in vitro over 15 days depending on the molecular weight of the hydrophobic part of the polymer matrix. These new systems where anti-cancer therapeutics like Taxol and iron oxide nanoparticles (IOs) are co-encapsulated into new facile polymeric nanoparticles, could be addressed as potential multifunctional vehicles for simultaneous drug delivery and targeting imaging as well as real time monitoring of therapeutic effects.

Abstract: This study comprises the first application of the Passive Flux Meter (PFM) for the measurement of chlorinated aliphatic hydrocarbon (CAH) mass fluxes and Darcy water fluxes in groundwater at a European field site. The PFM was originally developed and applied to measurements near source zones. The focus of the PFM is extended from near source to plume zones. For this purpose, 48 PFMs of 1.4 m length were constructed and installed in eight different monitoring wells in the source and plume zone of a CAH-contaminated field site located in France. The PFMs were retrieved, sampled, and analyzed after 3 to 11 weeks of exposure time, depending on the expected contaminant flux. PFM evaluation criteria include analytical, technical, and practical aspects as well as conditions and applicability. PFM flux data were compared with so-called traditional soil and groundwater concentration data obtained using active sampling methods. The PFMs deliver reasonable results for source as well as plume zones. The limiting factor in the PFM applicability is the exposure time together with the groundwater flux. Measured groundwater velocities at the field site range from 2 to 41 cm/day. Measured contaminant flux data raise up to 13 g/m(2)/day for perchloroethylene in the plume zone. Calculated PFM flux averaged concentration data and traditional concentration data were of similar magnitude for most wells. However, both datasets need to be compared with reservation because of the different sampling nature and time. Two important issues are the PFM tracer loss during installation/extraction and the deviation of the groundwater flow field when passing the monitoring well and PFM. The demonstration of the PFM at a CAH-contaminated field site in Europe confirmed the efficiency of the flux measurement technique for source as well as plume zones. The PFM can be applied without concerns in monitoring wells with European standards. The acquired flux data are of great value for the purpose of site characterization and mass discharge modeling, and can be used in combination with traditional soil and groundwater sampling methods.

Abstract: The combination of a non-thermal plasma with catalysis is considered as a sustainable indoor air purification technology to achieve complete oxidation at reduced energy cost with a longer electrode lifetime. An optimal window of operation for plasma assisted catalysis is found by varying the polarity, the applied voltage, the relative humidity of the gas phase and the configuration of the plasma reactor. The results show that, in general, negative corona discharge can obtain higher nitric oxide (NO) conversion efficiencies compared to positive corona. It is also clear that at higher applied voltages, higher conversion efficiency can be reached. The effect of relative humidity, however, is not found to be significant in the range (0 20.3 %) tested in this work. Additionally, the configuration of the plasma reactor is changed by varying the amount of pins that are attached at the collector electrode. The results show that there is an optimum at 10 pairs of pins to obtain a high conversion efficiency of NO. By applying a coating on the collector electrode of the plasma reactor, it is possible to see the influence of the coating on the performance of the plasma system, which was operating in the previously found optimal window. It stands clear that the use of a plasma assisted catalysis system has high potential as an integrated and sustainable indoor air purification technology.

Abstract: Gold-silver alloy nanoparticles display surface plasmon resonance (SPR) over a broad range of the UV-vis spectrum. We propose a model to predict the SPR wavelength of gold-silver alloy colloids based on the combined effect of alloy composition and particle size. The SPR wavelength is derived from extinction spectra simulated using available experimental dielectric constant data and accounts for particle size by applying Mie theory. Comparison of calculated values with experimental data evidences the accuracy of the model. The new SPR wavelength estimation tool will be of particular interest for developing dedicated bimetallic plasmonic nanostructures.

Abstract: Unlike the profound knowledge of the reaction mechanisms occurring in water phase photocatalysis, still fairly little is known on the reaction mechanisms occurring on the catalyst surface when dealing with gaseous pollutants. Unfortunately, there are some differences between both reactions. For one, there are no abundant hydroxyl radicals present in the gas phase, so that possibly other species prove to be important in abating the pollutant. In order to unravel the mysteries of gas phase photocatalytic reaction pathways, in situ techniques must be used to allow the detection and identification of reaction intermediates on a working catalyst. Several techniques were already used in the past, of which Fourier transform infrared spectroscopy seems to be the most versatile. This review will therefore give a selective overview of different spectroscopic reaction cells constructed for the in situ study of photocatalytic gas phase reactions.

Abstract: One of the most relevant problems in ship construction and maintenance nowadays concerns the corrosion in the double hull space ballast tanks of modern merchant vessels. On the one hand, there is a general consensus that the economic life span of such a vessel depends primarily upon the corrosion state of its ballast tanks, while on the other hand, the position of these tanks, squeezed between the outer hull and the loading tanks, makes routine inspection and maintenance almost impossible. Today, ship's ballast tanks are usually constructed in grade A steel and protected with a standard epoxy coating, backed up with sacrificial zinc anodes. Such a construction has been applied without significant alterations for many years. However, the objective of this economic study is to compare this construction method with some feasible alternatives. The considered alternatives are: (1) an increase of the scantlings, eliminating the necessity to replace corroded steel but diminishing the cargo carrying capacity of the ship, (2) application of the novel and more durable TSCF25 coating (3), the use of corrosion resistant steel in ship construction or (4) a standard PSPC15 coating combined with lifetime lasting aluminum sacrificial anodes. After running each alternative through a cost model including an extensive sensitivity analysis, it is concluded that the durable coating and the use of lifetime lasting aluminum anodes are bound to improve the actual basic tank concept. Corrosion resistant steel becomes attractive depending upon the evolution of the international steel market.

Abstract: The feasibility of algae harvesting with submerged flat panel membranes was investigated as pre-concentration step prior to centrifugation. Polishing of the supernatant coming from the centrifuge was evaluated as well. The effect of membrane polymer (polyvinyl chloride [PVC], polyethersulfone polyvinyl-pyrollidone [PES-PVP], poly vinylidene fluoride [PVDF]), pore size (microfiltration [MF], ultrafiltration [UF]), algae cell concentrations and species were investigated at lab-scale. In addition, backwashing as fouling control was compared to standard relaxation. PVDF was the superior polymer, and UF showed better fouling resistance. Backwashing outperformed relaxation in fouling control. The backwashable membranes allowed up to 300% higher fluxes compared to commercial flat panel benchmark (PVC) membranes. Estimations on energy consumption for membrane filtration followed by centrifugation revealed relatively low values of 0.169 kW h/kg of dry weight of algae compared to 0.5 kW h/kg for algae harvesting via classical centrifuge alone. (C) 2012 Elsevier Ltd. All rights reserved.