Abstract: Novel stable ultra-thin phases of europium oxide are investigated by means of state-of-the-art first principles calculations. Total energy calculations show that single layers of EuO2 and Eu(OH)(2) can be stabilized in an octahedrally coordinated (1T) atomic structure. However, phonon calculations reveal that although both structures are energetically feasible, only the 1T-EuO2 phase has dynamical stability. The phonon spectrum of 1T-EuO2 displays three Raman active modes; a non-degenerate out-of-plane A(1g) mode at 353.5 cm(-1) and two doubly-degenerate in-plane E-g modes at 304.3 cm(-1). Furthermore, magnetic ground state and electronic band dispersion calculations show that the single layer EuO2 is a metal with net magnetic moment of 5(mu B) per unitcell resulting in a half-metallic ferrimagnetic behavior. Moreover, robustness of the half-metallic ferrimagnetic characteristics of EuO2 is confirmed by the application of electric field and charging. Single layer 1T-EuO2, with its stable ultra-thin structure and half-metallic ferrimagnetic feature, is a promising novel material for nanoscale electronic and spintronic applications.

Abstract: Vanadium dioxide (VO2) is a much-discussed material for oxide electronics and neuromorphic computing applications. Here, heteroepitaxy of VO2 is realized on top of oxide nanosheets that cover either the amorphous silicon dioxide surfaces of Si substrates or X-ray transparent silicon nitride membranes. The out-of-plane orientation of the VO2 thin films is controlled at will between (011)(M1)/(110)(R) and (-402)(M1)/(002)(R) by coating the bulk substrates with Ti0.87O2 and NbWO6 nanosheets, respectively, prior to VO2 growth. Temperature-dependent X-ray diffraction and automated crystal orientation mapping in microprobe transmission electron microscope mode (ACOM-TEM) characterize the high phase purity, the crystallographic and orientational properties of the VO2 films. Transport measurements and soft X-ray absorption in transmission are used to probe the VO2 metal-insulator transition, showing results of a quality equal to those from epitaxial films on bulk single-crystal substrates. Successful local manipulation of two different VO2 orientations on a single substrate is demonstrated using VO2 grown on lithographically patterned lines of Ti0.87O2 and NbWO6 nanosheets investigated by electron backscatter diffraction. Finally, the excellent suitability of these nanosheet-templated VO2 films for advanced lensless imaging of the metal-insulator transition using coherent soft X-rays is discussed.

Abstract: Particle-in-cell/Monte Carlo collision (PIC/MCC) simulations are performed to investigate the asymmetric secondary electron emission (SEE) effects when electrons strike two different material electrodes in low pressure capacitively coupled plasmas (CCPs). To describe the electron-surface interactions, a realistic model, considering the primary electron impact energy and angle, as well as the corresponding surface property-dependent secondary electron yields, is employed in PIC/MCC simulations. In this model, three kinds of electrons emitted from the surface are considered: (i) elastically reflected electrons, (ii) inelastically backscattered electrons, and (iii) electron induced secondary electrons (SEs, i.e., delta-electrons). Here, we examined the effects of electron-surface interactions on the ionization dynamics and plasma characteristics of an argon discharge. The discharge is driven by a voltage source of 13.56MHz with amplitudes in the range of 200-2000V. The grounded electrode material is copper (Cu) for all cases, while the powered electrode material is either Cu or silicon dioxide (SiO2). The simulations reveal that the electron impact-induced SEE is an essential process at low pressures, especially at high voltages. Different electrode materials result in an asymmetric response of SEE. Depending on the instantaneous local sheath potential and the phase of the SEE, these SEs either are reflected by the opposite sheath or strike the electrode surface, where they can induce delta-electrons upon their residual energies. It is shown that highly energetic delta-electrons contribute significantly to the ionization rate and a self-bias forms when the powered electrode material is assumed to be made of SiO2. Complex dynamics is observed due to the multiple electron-surface interaction processes and asymmetric yields of SEs in CCPs.

Abstract: By employing first-principles calculations within the framework of density functional theory, we investigated the structural, electronic, and magnetic properties of graphene and various two-dimensional carbon-nitride (2DNC) nanosheets. The different 2DCN gives rise to diverse electronic properties such as metals (C3N2), semimetals (C4N and C9N4), half-metals (C4N3), ferromagnetic-metals (C9N7), semiconductors (C2N, C3N, C3N4, C6N6, and C6N8), spin-glass semiconductors (C10N9 and C14N12), and insulators (C2N2). Furthermore, the effects of adsorption and substitution of hydrogen atoms as well as N-vacancy defects on the electronic and magnetic properties are systematically studied. The introduction of point defects, including N vacancies, interstitial H impurity into graphene and different 2DCN crystals, results in very different band structures. Defect engineering leads to the discovery of potentially exotic properties that make 2DCN interesting for future investigations and emerging technological applications with precisely tailored properties. These properties can be useful for applications in various fields such as catalysis, energy storage, nanoelectronic devices, spintronics, optoelectronics, and nanosensors. Published under license by AIP Publishing.

Abstract: Mesosiderite meteorites consist of a mixture of crustal basaltic or gabbroic material and metal. Their formation process is still debated due to their unexpected combination of crust and core materials, possibly derived from the same planetesimal parent body, and lacking an intervening mantle component. Mesosiderites have experienced an extremely slow cooling rate from ca. 550 degrees C, as recorded in the metal (0.25-0.5 degrees C/Ma). Here we present a detailed investigation of exsolution features in pyroxene from the Antarctic mesosiderite Asuka (A) 09545. Geothermobarometry calculations, lattice parameters, lamellae orientation, and the presence of clinoenstatite as the host were used in an attempt to constrain the evolution of pyroxene from 1150 to 570 degrees C and the formation of two generations of exsolution lamellae. After pigeonite crystallization at ca. 1150 degrees C, the first exsolution process generated the thick augite lamellae along (100) in the temperature interval 1000-900 degrees C. By further cooling, a second order of exsolution lamellae formed within augite along (001), consisting of monoclinic low-Ca pyroxene, equilibrated in the temperature range 900-800 degrees C. The last process, occurring in the 600-500 degrees C temperature range, was likely the inversion of high to low pigeonite in the host crystal, lacking evidence for nucleation of orthopyroxene. The formation of two generations of exsolution lamellae, as well as of likely metastable pigeonite, suggest non-equilibrium conditions. Cooling was sufficiently slow to allow the formation of the lamellae, their preservation, and the transition from high to low pigeonite. In addition, the preservation of such fine-grained lamellae limits long-lasting, impact reheating to a peak temperature lower than 570 degrees C. These features, including the presence of monoclinic low-Ca pyroxene as the host, are reported in only a few mesosiderites. This suggests a possibly different origin and thermal history from most mesosiderites and that the crystallography (i.e., space group) of low-Ca pyroxene could be used as parameter to distinguish mesosiderite populations based on their cooling history.

Abstract: The limitation in time and length scale is a major issue of molecular dynamics (MD) simulation. Although several methods have been developed to extend the MD time scale, their performance usually deteriorates with increasing system size. Therefore, an acceleration method which is applicable to large systems is required to bridge the gap between the MD simulations and target phenomena. In this study, an accelerated MD method for large system is developed based on the collective variable-driven hyperdynamics (CVHD) method [K.M. Bal and E.C. Neyts, 2015]. The key idea is to run CVHD in parallel with rate control and accelerate multiple possible events simultaneously. Using this novel method, carbon diffusion in bcc-iron bicrystal with grain boundary is examined as an application for practical materials. Carbon atoms reaching at the grain boundary are trapped whereas carbon atoms in the bulk region diffuse randomly, and both dynamic regimes can be simultaneously accelerated with the parallel CVHD technique.

Abstract: Branched plasmonic nanocrystals (NCs) have attracted much attention due to electric field enhancements at their tips. Seeded growth provides routes to NCs with defined branching patterns and, in turn, near‐field distributions with defined symmetries. Here, a systematic analysis was undertaken in which seeds containing different distributions of planar defects were used to grow branched NCs in order to understand how their distributions direct the branching. Characterization of the products by multimode electron tomography and analysis of the NC morphologies at different overgrowth stages indicate that the branching patterns are directed by the seed defects, with the emergence of branches from the seed faces consistent with minimizing volumetric strain energy at the expense of surface energy. These results contrast with growth of branched NCs from single‐crystalline seeds and provide a new platform for the synthesis of symmetrically branched plasmonic NCs.

Abstract: A gliding arc (GA) plasma has great potential for CO2 conversion into value-added chemicals, because of its high energy efficiency. To improve the application, a 2D/3D fluid model is needed to investigate the CO2 conversion mechanisms in the actual discharge geometry. Therefore, the complex CO2 chemical kinetics description must be reduced due to the huge computational cost associated with 2D/3D models. This paper presents a chemistry reduction method for CO2 plasmas, based on the so-called directed relation graph method. Depending on the defined threshold values, some marginal species are identified. By means of a sensitivity analysis, we can further reduce the chemistry set by removing one by one the marginal species. Based on the socalled flux-sensitivity coupling, we obtain a reduced CO2 kinetics model, consisting of 36 or 15 species (depending on whether the 21 asymmetric mode vibrational states of CO2 are explicitly included or lumped into one group), which is applied to a GA discharge. The results are compared with those predicted with the full chemistry set, and very good agreement is reached. Moreover, the range of validity of the reduced CO2 chemistry set is checked, telling us that this reduced set is suitable for low power GA discharges. Finally, the time and spatial evolution of the CO2 plasma characteristics are presented, based on a 2D model with the reduced kinetics.

Abstract: Nitrogen oxyanions and oxyacids are important agents in atmospheric chemistry and medical biology. Although their chemical behavior in solution is relatively well understood, they may behave very differently at the water/air interface of atmospheric aerosols or at the membrane/water interface of cells. Here, we developed a fully classical model for molecular dynamics simulations of NO3−, NO2−, HNO3, and HNO2 in the framework of the GROMOS 53A6 and 54A7 force field versions. The model successfully accounted for the poorly structured solvation shell and ion pairing tendency of NO3−. Accurate pure-liquid properties and hydration free energies were obtained for the oxyacids. Simulations at the water/air interface showed a local enrichment of HNO3 and depletion of NO3−. The effect was discussed in light of earlier spectroscopic data and ab initio calculations, suggesting that HNO3 behaves as a weaker acid at the surface of water. Our model will hopefully allow for efficient and accurate simulations of nitrogen oxyanions and oxyacids in solution and at microheterogeneous interface environments.

Abstract: A series of mixed nanocomposite materials was synthetized, containing a Ferrite phase type Zn1-xNixFe2O4 and a Freudenbergite phase type Na2Fe2Ti6O16, where x = 0; 0.2; 0.4; 0.6; 0.8; 1. The choice for this combination is based on the good adsorption properties of Freudenbergite for dye molecules, and the small bandgap energy of Ferrite spinel, allowing activation of the catalysts under visible light irradiation. A two steps synthesis protocol was used to obtain the smart-removal nanocomposites. Firstly, the spinel structure was obtained via the co-precipitation route followed by the addition of the Ti-source and formation of the Freudenbergite system. The role of cations on the formation mechanism and an interesting interchange of cations between spinel and Freudenbergite structures was clarified by a TEM study. Part of the Ti4+ penetrated the spinel structure and, at the same time, part of the Fe3+ formed the Freudenbergite system. The photocatalytic activity was studied under visible light, reaching for the best catalysts a 67% and 40% mineralization degree for methylene blue and rhodamine 6G respectively, after 6 h of irradiation. In the same conditions, the well-known commercial P25 (Degussa) managed to mineralize only 12% and 3% of methylene blue and rhodamine 6G, respectively. Due to the remarkable magnetic properties of Ferrites, a convenient recovery and reuse of the catalysts is possible after the photocatalytic tests. Based on the excellent catalytic performance of the nanocomposites under visible light and their ease of separation out of the solution after the catalytic reaction, the newly developed composite catalysts are considered very effective for wastewater treatment.

Abstract: Winter peaks in Belgian electricity demand are significantly higher than the summer peaks, creating a greater potential for imbalances between demand and supply. This potential is exacerbated because of the risk of outages in its ageing nuclear power plants, which are being phased out in the medium term. This paper conducts a choice experiment to investigate the acceptability of a load control-based demand response program in the winter months. It surveys 186 respondents on their willingness to accept limits on the use of home appliances in return for a compensation. Results indicate that respondents are most affected by the days of the week that their appliance usage would be curtailed, and by the compensation they would receive. The willingness to enroll in a program increases with age, environmental consciousness, home ownership, and lower privacy concerns. The analysis predicts that 95% of the sample surveyed could enroll in a daily load control program for a compen- sation of €41 per household per year. Thus while an initial rollout among older and more pro-environment homeowners could be successful, a wider implementation would require an explanation of its environmental and financial benefits to the population, and a greater consideration of their data privacy concerns.

Abstract: Neutron diffraction experiments conducted at 5 K in a magnetic field 0 < H/kOe < 50 have shown that the monoclinic perovskite La3Ni2TaO9 behaves as a relaxor ferromagnet. Compositions in the series La3Ni2SbxTayNb1–x–yO9 have been synthesized in polycrystalline form. Electron microscopy, X–ray diffraction and neutron diffraction have shown that the solid solutions are largely homogeneous and monophasic. Magnetometry and neutron diffraction have shown that the relaxor magnetisation persists in low fields when x + y = 1 but is rapidly diminished by the introduction of niobium. This change in magnetic behaviour is ascribed to the differences in the d–orbital energies of Sb5+, Nb5+ and Ta5+.

Abstract: While the concept of ecosystem services which links biodiversity to human wellbeing, is by now well-known, its translation into actual management decisions is still uneven. African Biosphere Reserves, which are to be living labs for sustainable development, embody the idea of synergies between people and nature. Gaining knowledge about the provision, the use and the trends of ecosystem services in these reserves is essential to ensure their global change-proof management. The diversity of rapidly evolving ecosystem services assessment tools requires a systematic and informed selection, in order to ensure that prospective tool users select the most adequate tool, aligned to their needs and context. Based on a Delphi survey of future tool users, and on a review of ecosystem services assessment tools, we propose guidance to users to select the most suited tool based on the context of African Biosphere Reserves, and on tool requirements regarding data input, necessary skills, outputs and types of ecosystem services addressed. The use of the Delphi survey and the focus on African Biosphere Reserves are new elements that contribute to the theory and practice of ecosystem services assessment.

Abstract: Socio-technical transitions are often hindered by the resilience of existing infrastructures, as policymakers are reluctant to invest in novel products or services. Using the example of carbon capture and utilisation (CCU) based fuels, we set up a discrete choice experiment to assess whether European policymakers have a tendency to avoid investing in novel, and more disruptive technologies, and rather prefer to invest in technologies that resemble the incumbent. Results indicate that policymakers prefer to allocate funding to dominant technologies. The results also revealed an overall positive perception of CCU technologies among policymakers. As the commercialisation of such products and processes continues, acceptance among this group of stakeholders is key.

Abstract: Waste treatment taxation is a popular policy instrument in many European countries and regions. Its impact on household waste has extensively been researched. However, only little research exists which looks into the impact of waste treatment taxation on industrial waste generation. Nevertheless, industrial waste constitutes more than ninety percent of waste generated in the European Union. This study assesses the impact of an incineration tax on the generation of industrial plastic waste in Flanders, Belgium. We conduct different types of econometrical panel analyzes and provide statistical evidence that firms show lagged behavior, which means that the previous year’s waste generation partly determines the current year’s. The dynamic panel estimations show robust results, indicating that a growth of incineration taxes exert significant negative effects on the growth of industrial plastic waste generation. This result offers no argument to iteratively raise incineration taxes. We conclude that incineration taxation is meaningful if tax rates are set according to the prevailing market conditions, i.e. taking into account the marginal costs of alternatives for incineration. In the short run, the effectiveness of taxation will quickly diminish due to the rapidly rising marginal costs of waste reduction. In the long run, extra recycling capacity is needed to recycle the minimized waste fraction. The role of taxation in the long run is to maintain an equilibrium in which recycling is preferred by the market.