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: The properties of alternative metals to Cu and W for interconnect applications are reviewed based on first-principles simulations and benchmarked in terms of intrinsic bulk resistivity and electromigration.

Abstract: The Quantemol database (QDB) provides cross sections and rates of processes important for plasma models; heavy particle collisions (chemical reactions) and electron collision processes are considered. The current version of QDB has data on 28 917 processes between 2485 distinct species plus data for surface processes. These data are available via a web interface or can be delivered directly to plasma models using an application program interface; data are available in formats suitable for direct input into a variety of popular plasma modeling codes including HPEM, COMSOL, ChemKIN, CFD-ACE+, and VisGlow. QDB provides ready assembled plasma chemistries plus the ability to build bespoke chemistries. The database also provides a Boltzmann solver for electron dynamics and a zero-dimensional model. Thesedevelopments, use cases involving O₂, Ar/NF₃, Ar/NF₃/O₂, and He/H₂O/O₂chemistries, and plans for the future are presented.

Abstract: The quartic force fields of FNO and CINO have been computed at the CCSD(T)/cc-pVTZ level. Using an ''augmented'' basis set dramatically improves results for FNO but has no significant effect for CINO. The best computed force field for FNO yields harmonic frequencies and fundamentals in excellent agreement with experiment. Overall, the force fields proposed in the present work are probably the most reliable ones ever published for these molecules. Total atomization energies have been computed using basis sets of spdfg quality: our best estimates are Sigma D-0 = 208.5 +/- 1 and 185.4 +/- 1 kcal/mol for FN0 and CINO, respectively. The computed value for FNO suggests a problem with the established experimental heat of formation. Thermodynamic tables in JANAF style at 100-2000 K are presented for both FNO and CINO.

Abstract: The rate, selectivity and efficiency of plasma-based conversion processes is strongly affected by nonequilibrium phenomena. High concentrations of vibrationally excited molecules are such a plasma-induced effect. It is frequently assumed that vibrationally excited molecules are important in plasma catalysis because their presence lowers the apparent activation energy of dissociative chemisorption reactions and thus increases the conversion rate. A detailed atomic-level understanding of vibrationally stimulated catalytic reactions in the context of plasma catalysis is however lacking. Here, we couple a recently developed statistical model of a plasma-induced vibrational nonequilibrium to molecular dynamics simulations, enhanced sampling methods, and machine learning techniques. We quantify the impact of a vibrational nonequilibrium on the dissociative chemisorption barrier of H2 and CH4 on nickel catalysts over a wide range of vibrational temperatures. We investigate the effect of surface structure and compare the role of different vibrational modes of methane in the dissociation process. For low vibrational temperatures, very high vibrational efficacies are found, and energy in bend vibrations appears to dominate the dissociation of methane. The relative impact of vibrational nonequilibrium is much higher on terrace sites than on surface steps. We then show how our simulations can help to interpret recent experimental results, and suggest new paths to a better understanding of plasma catalysis.

Abstract: The reactivity of platinized ultramicroelectrodes (Pt-black UMEs) towards superoxide anion O-2(.-), an unstable Reactive Oxygen Species (ROS), and its relatives, H2O2 and O-2, was studied. Voltammetric studies in PBS demonstrate that Pt-black UMEs provide: i) a well-resolved reversible redox signature for O-2(.-) detected in both alkaline and physiological buffers (pH 12 and 7.4); ii) irreversible oxidation and reduction waves for H2O2 at pH 7.4. The oxygen reduction reaction (ORR) at Pt-black surfaces solely yields H2O2 (2 electrons/2 H+) at physiological pH. Consequently, Pt-black UMEs allow to sense different ROS including superoxide anion for future biomedical or physico-chemical investigations.

Abstract: The recent energy crisis revealed that there is a strong need to replace hydrocarbon-fueled industrial nitrogen fixation processes by alternative, more sustainable methods. In light of this, plasma-based nitrogen fixation remains one of the most promising options, considering both theoretical and experimental aspects. Lately, plasma interacting with water has received considerable attention in nitrogen fixation applications as it can trigger a unique gas- and liquid-phase chemistry. Within this context, a critical exploration of plasma-assisted nitrogen fixation with or without water presence is of great interest with an emphasis on energy costs, particularly in plasma reactors which have potential for large-scale industrial application. In this work, the presence of water in a multi-pin plasma system on nitrogen oxidation is experimentally investigated by comparing two pulsed negative DC voltage plasmas in metal–metal and metal–liquid electrode configurations. The plasma setups are designed to create similar plasma properties, including plasma power and discharge regime in both configurations. The system energy cost is calculated, considering nitrogen-containing species generated in gas and liquid phases as measured by a gas analyzer, nitrate sensor, and a colorimetry method. The energy cost profile as a function of specific energy input showed a strong dependency on the plasma operational frequency and the gas flow rate, as a result of different plasma operation regimes and initiated reverse processes. More importantly, the presence of the plasma/liquid interface increased the energy cost up to 14 ± 8%. Overall, the results showed that the presence of water in the reaction zone has a negative impact on the nitrogen fixation process.

Abstract: The requirements for new technologies to serve as anticancer agents go far beyond their toxicity potential. Novel applications also need to be safe on a molecular and patient level. In a broader sense, this also relates to cancer metastasis and inflammation. In a previous study, the toxicity of an atmospheric pressure argon plasma jet in four human pancreatic cancer cell lines was confirmed and plasma treatment did not promote metastasis in vitro and in ovo. Here, these results are extended by additional types of analysis and new models to validate and define on a molecular level the changes related to metastatic processes in pancreatic cancer cells following plasma treatment in vitro and in ovo. In solid tumors that were grown on the chorion-allantois membrane of fertilized chicken eggs (TUM-CAM), plasma treatment induced modest to profound apoptosis in the tissues. This, however, was not associated with a change in the expression levels of adhesion molecules, as shown using immunofluorescence of ultrathin tissue sections. Culturing of the cells detached from these solid tumors for 6d revealed a similar or smaller total growth area and expression of ZEB1, a transcription factor associated with cancer metastasis, in the plasma-treated pancreatic cancer tissues. Analysis of in vitro and in ovo supernatants of 13 different cytokines and chemokines revealed cell line-specific effects of the plasma treatment but a noticeable increase of, e.g., growth-promoting interleukin 10 was not observed. Moreover, markers of epithelial-to-mesenchymal transition (EMT), a metastasis-promoting cellular program, were investigated. Plasma-treated pancreatic cancer cells did not present an EMT-profile. Finally, a realistic 3D tumor spheroid co-culture model with pancreatic stellate cells was employed, and the invasive properties in a gel-like cellular matrix were investigated. Tumor outgrowth and spread was similar or decreased in the plasma conditions. Altogether, these results provide valuable insights into the effect of plasma treatment on metastasis-related properties of cancer cells and did not suggest EMT-promoting effects of this novel cancer therapy.

Abstract: The role of the Cu atoms sputtered from the cathode material in a cylindrical hollow cathode discharge (HCD) and the corresponding Cu+ ions are studied with a self-consistent model based on the principle of Monte Carlo (MC) and fluid simulations. In order to obtain a more realistic view of the discharge processes, this model is coupled with other submodels, which describe the behavior of electrons, fast Ar atoms, Ar+ ions, and Ar metastable atoms, also based on the principles of MC and fluid simulations. Typical results are, among others, the thermalization profile of the Cu atoms, the fast Cu atom, the thermal Cu atom and Cu+ ion fluxes and densities, and the energy distribution of the Cu+ ions. It was found that the contribution of the Ar+ ions to the sputtering was the most significant, followed by the fast Ar atoms. At the cathode bottom, there was no net sputtered flux but a net amount of redeposition. Throughout the discharge volume, at all the conditions investigated, the largest concentration of Cu atoms was found in the lower half of the HCD, close to the bottom. Penning ionization was found the main ionization mechanism for the Cu atoms. The ionization degree of copper atoms was found to be in the same order as for the argon atoms (10-4). (c) 2005 American Institute of Physics.

Abstract: The scalability potential of low resistivity ternary metallic alloys (MAX) as an interconnect medium has been benchmarked against copper through first-principle simulations. We report that some carbon and nitrogen MAX phases have the potential to display a reduced sensitivity of their intrinsic resistivity to scaling, while showing improved electromigration properties.

Abstract: The six platinum group elements (Ru, Rh, Pd, Os, Ir and Pt) can be determined in geological samples down to the μg kg−1 level, by using nickel sulphide fire assay and neutron activation of the residue ramaining after dissolution of the nickel sulphide button in concentrated hydrochloric acid. Losses for the platinum group elements during this dissolution step are usually insignificant, except when the elements are present at ultra-trace levels. The can be recovered from the filtrate by coprecipitation with tellerium. The latter approach also permits determination of silver, which is significantly lost in the hydrochloric acid treatment (recovery <98% instead of typically ≈ 10%). The coprecipitation with tellurium considerably improves the results for gold (recovery ≈ 95% instead of typically 75%).

Abstract: The structural and electronic properties of silicene and germanene on metallic and non-metallic substrates are investigated theoretically, using first-principles simulations. We first study the interaction of silicene with Ag(111) surfaces, focusing on the (4x4) silicene/Ag structure. Due to symmetry breaking in the silicene layer (nonequivalent number of top and bottom Si atoms), silicene is predicted to be semiconducting, with a computed energy gap of about 0.3 eV. However, the charge transfer occurring at the silicene/Ag(111) interface leads to an overall metallic system. We next investigate the interaction of silicene and germanene with hexagonal non-metallic substrates, namely ZnS and ZnSe. On reconstructed (semiconducting) (0001) ZnS or ZnSe surfaces, silicene and germanene are found to be semiconducting. Remarkably, the nature (indirect or direct) and magnitude of their energy band gap can be controlled by an out-of-plane electric field.

Abstract: The structural and vibrational properties of two-dimensional hexagonal silicon (silicene) and germanium (germanene) are investigated by means of first-principles calculations. It is predict that the silicene (germanene) structure with a small buckling of 0.44 (0.7 ) and bond lengths of 2.28 (2.44 ) is energetically the most favorable, and it does not exhibit imaginary phonon mode. The calculated non-resonance Raman spectra of silicene is characterized by a main peak at about 575 cm(-1), namely the G-like peak. For germanene, the highest peak is at about 290 cm(-1). Extensive calculations on armchair silicene nanoribbons and armchair germanene nanoribbons are also performed, with and without hydrogenation of the edges. The studies reveal other Raman peaks mainly distributed at lower frequencies than the G-like peak which could be attributed to the defects at the edges of the ribbons, thus not present in the Raman spectra of non-defective silicene and germanene. Particularly the Raman peak corresponding to the D mode is found to be located at around 515 cm(-1) for silicene and 270 cm(-1) for germanene. The calculated G-like and the D peaks are likely the fingerprints of the Raman spectra of the low-buckled structures of silicene and germanene.

Abstract: The technique of imaging time-of-flight secondary ion mass spectrometry (TOF-SIMS) and dual beam depth,profiling has been used to study the composition of the surface of tabular silver halide microcrystals. Analysis of individual microcrystals with a size well below 1 mum from a given emulsion is possible. The method is successfully applied for the characterization of silver halide microcrystals with subpercent global iodide concentrations confined in surface layers with a thickness below 5 nm. The developed TOF-SIMS analytical procedure is explicitly demonstrated for the molecular imaging of adsorbed thiocyanate layers (SCN) at crystal surfaces of individual crystals and for the differentiation of iodide conversion layers synthesized with KI and with AgI micrates (nanocrystals with a size between 10 and 50 nm). It can be concluded that TOF-SIMS as a microanalytical, surface-sensitive technique has some unique properties over other analytical techniques for the study of complex structured surface layers of silver halide microcrystals. This offers valuable information to support the synthesis of future photographic emulsions.

Abstract: The treatment of a well plate by an atmospheric pressure plasma jet is common for<italic>in vitro</italic>plasma medicine research. Here, reactive species are largely produced through the mixing of the jet effluent with the surrounding atmosphere. This mixing can be influenced not only by the ambient conditions, but also by the geometry of the treated well. To limit this influence and control the atmosphere, a shielding gas is sometimes applied. However, the interplay between the gas shield and the well geometry has not been investigated. In this work, we developed a 2D-axisymmetric computational fluid dynamics model of the kINPen plasma jet, to study the mixing of the jet effluent with the surrounding atmosphere, with and without gas shield. Our computational and experimental results show that the choice of well type can have a significant influence on the effluent conditions, as well as on the effectiveness of the gas shield. Furthermore, the geometry of the shielding gas device can substantially influence the mixing as well. Our results provide a deeper understanding of how the choice of setup geometry can influence the plasma treatment, even when all other operating parameters are unchanged.