Abstract: Transmission electron microscopy and finite element-based dislocation simulations were combined to study the development of dislocation microstructures after cyclic deformation of single crystal and bicrystal Ni micropillars oriented for multi-slip. A direct correlation between large accumulation of plastic strain and the presence of dislocation cell walls in the single crystal micropillars was observed, while the presence of the grain boundary hampered the formation of wall-like structures in agreement with a smaller accumulated plastic strain. Automated crystallographic orientation and nanostrain mapping using transmission electron microscopy revealed the presence of lattice heterogeneities associated to the cell walls including long range elastic strain fields. By combining the nanostrain mapping with an inverse modelling approach, information about dislocation density, line orientation and Burgers vector direction was derived, which is not accessible otherwise in such dense dislocation structures. Simulations showed that the image forces associated with the grain boundary in this specific bicrystal configuration have only a minor influence on dislocation behavior. Thus, the reduced occurrence of “mature” cell walls in the bicrystal can be attributed to the available volume, which is too small to accommodate cell structures.

Abstract: We present an approach to incorporate the effect of vibrational nonequilibrium in molecular dynamics (MD) simulations. A perturbed canonical ensemble, in which selected modes are excited to higher temperature while all others remain equilibrated at low temperature, is simulated by applying a specifically tailored bias potential. Our method can be readily applied to any (classical or quantum mechanical) MD setup at virtually no additional computational cost and allows the study of reactions of vibrationally excited molecules in nonequilibrium environments such as plasmas. In combination with enhanced sampling methods, the vibrational efficacy and mode selectivity of vibrationally stimulated reactions can then be quantified in terms of chemically relevant observables, such as reaction rates and apparent free energy barriers. We first validate our method for the prototypical hydrogen exchange reaction and then show how it can capture the effect of vibrational excitation on a symmetric SN2 reaction and radical addition on CO2.

Abstract: Understanding the folding and stability of membrane proteins is of great importance in protein science. Recently, osmolytes and ionic liquids (ILs) are increasingly being used as drug delivery systems in the biopharmaceutical industry. However, the stability of membrane proteins in the presence of osmolytes and ILs is not yet fully understood. Besides, the effect of oxidative stress on membrane proteins with osmolytes or ILs has not been investigated. Therefore, we studied the influence of osmolytes and ILs as co-solvents on the stability of a model membrane protein (i.e., Bacteriorhodopsin in purple membrane of Halobacterium salinarum), using UV–Vis spectroscopy and molecular dynamics (MD) simulations. The MD simulations allowed us to determine the flexibility and solvent accessible surface area (SASA) of Bacteriorhodopsin protein in the presence and/or absence of cosolvents, as well as to carry out principal component analysis (PCA) to identify the most important movements in this protein. In addition, by means of UV–Vis spectroscopy we studied the effect of oxidative stress generated by cold atmospheric plasma on the stability of Bacteriorhodopsin in the presence and/or absence of co-solvents. This study is important for a better understanding of the stability of proteins in the presence of oxidative stress.

Abstract: Titanium dioxide (TiO2) is a unique material for biosensing applications due to its capability of hosting enzymes. For the first time, we show that TiO2 can accumulate reactive oxygen species (ROS) under daylight irradiation and can support the catalytic cycle of horseradish peroxidase (HRP) without the need of H2O2 to be present in the solution. Phenolic compounds, such as hydroquinone (HQ) and 4-aminophenol (4-AP), were detected amperometrically in flow-injection analysis (FIA) mode via the use of an electrode modified with TiO2 impregnated with HRP. In contrast to the conventional detection scheme, no H2O2 was added to the analyte solution. Basically, the inherited ability of TiO2 to generate reactive oxygen species is used as a strategy to avoid adding H2O2 in the solution during the detection of phenolic compounds. Electron paramagnetic resonance (EPR) spectroscopy indicates the presence of ROS on titania which, in interaction with HRP, initiate the electrocatalysis toward phenolic compounds. The amperometric response to 4-AP was linear in the concentration range between 0.05 and 2 μM. The sensitivity was 0.51 A M–1 cm–2, and the limit of detection (LOD) 26 nM. The proposed sensor design opens new opportunities for the detection of phenolic traces by HRP-based electrochemical biosensors, yet in a more straightforward and sensitive way following green chemistry principles of avoiding the use of reactive and harmful chemical, such as H2O2.

Abstract: Atmospheric dust deposition on plants enables the collection of site-specific particulate matter (PM). Knowing the morphology and composition of PM aids in disclosing their emitting sources as well as the associated human health risk. Therefore, this study aimed for a leaf-level holistic analysis of dust accumulation on plant leaves. Plant species (ivy and strawberry) with distinct leaf macro- and micro-morphology were exposed during 3 months at a moderate road traffic site in Antwerp, Belgium. Leaves collected every three weeks were analyzed for their magnetic signature, morphology and elemental content, by a combination of techniques (biomagnetic analyses, ED-XRF, HR-ICP-MS, SEM). Dust accumulation on the leaves was observed both visually (SEM) and magnetically, while the metal enrichment was limited (only evident for Cr) and more variable over time. Temporal dynamics during the second half of the exposure period, due to precipitation events and reduction of atmospheric pollution input, were evidenced in our results (elements/magnetically/SEM). Ivy accumulated more dust than strawberry leaves and seemed less susceptible to wash-off, even though strawberry leaves contain trichomes and a rugged micromorphology, leaf traits considered to be important for capturing PM. The magnetic enrichment (in small-grained, SD/PSD magnetite particles), on the other hand, was not species-specific, indicating a common contributing source. Variations in pollution contributions, meteorological phenomena, leaf traits, particle deposition (and encapsulation) versus micronutrients depletion, are discussed in light of the conducted monitoring campaign. Although not completely elucidative, the complex, multifactorial process of leaf dust accumulation can better be understood through a combination of techniques.

Abstract: Buildings are responsible for 40% of our worldwide energy consumption and 50% of this energy is converted for Heating Ventilation Air Conditioning (HVAC) systems in buildings. The increasing share of renewable energy production required to make the transition towards a carbon neutral energy system challenges the stability of the grid. Through demand response it becomes possible to activate these systems in support of grid balancing. However, this flexibility is currently not rewarded in the market. We simulate a domestic water heater participating in the balancing of the electricity net and calculated the revenue from this action. We simulate a water heater in connection with an Economic Model Predictive Controller (EMPC) which takes future usage, energy cost, and reward for delivering balanced power into account. We show that the choice of an EMPC controller is valid as it allows the setpoint to change if certain conditions are met, leading to a more optimal revenue stream from selling flexibility. We find that the economic benefits of participating in delivering balancing power is considerable and offset an increase in energy costs. The increase in energy consumption could be justified as the participation in net stabilisation allows the macro-system to integrate more renewable energy sources. More importantly, the simulations also show that the poorer the energy performance of the water heater, the more flexibility can be sold. From a policy point of view, a minimal energy performance should be determined before allowing participation in net stabilisation.

Abstract: Purpose Social indicators are not easy to be quantitatively analyzed, although at the local scale, the social impacts might be relevant and important. Using the existing approaches for both quantitative and semi-qualitative measurements, this study aims to assess the social impacts of a company working on algae production systems in Belgium through social life cycle analysis (SLCA). By highlighting the opportunities and challenges on the way of applying the existing SLCA approaches at company level, the objective of this study is to contribute to the development of a suitable and clear SLCA approach when a company is considered as the unit of analysis. Methods Based on the list of potential social impact categories suggested by the United Nations Environment Program/Society of Environmental Toxicology and Chemistry (UNEP/SETAC) guidelines (2009) for SLCA, three stakeholder groups (workers, consumers, and local community) and three subcategories associated with each stakeholder group were identified as the most relevant for carbon capture and utilization technologies. Company and sector level data were collected using existing documents and reports, and the data were analyzed and scored using a combined quantitative and semi-quantitative approach to develop a social assessment model for the case study. Results and discussion The company appears to perform well for all the evaluated social indicators except the one related to the subcategory “equal opportunity/discrimination for workers” for which the share of women employed is lower compared with the sector-level data. The results of our assessment were further discussed regarding the challenges and limitations of performing SLCA at the company level. Based on our experience, the validity of the outcomes is significantly influenced by the data availability, the generality of the indicators introduced within the UNEP/SETAC guidelines, and the subjectivity in data collection for the semi-quantitative assessment among others. Conclusions By highlighting the difficulties and challenges of applying the SLCA at the company level, our study provides a starting point for improving the quantitative assessment and monitoring social implications at the company level within a regional foreground in Europe.

Abstract: Using the first-principles calculations, we explore the structural and novel electronic/optical properties of the C2N nanosheet. To this goal, we systematically investigate the affect of layer thickness, electrical field and strain on the electronic properties of the C2N nanosheet. By increasing the thickness of C2N, we observed that the band gap decreases. Moreover, by applying an electrical field to bilayer C2N, the band gap decreases and a semiconductor-to-metal transition can occur. Our results also confirm that uniaxial and biaxial strain can effectively alter the band gap of C2N monolayer. Furthermore, we show that the electronic and magnetic properties of C2N can be modified by the adsorption and substitution of various atoms. Depending on the species of embedded atoms, they may induce semiconductor (O, C, Si and Be), metal (S, N, P, Na, K, Mg and Ca), dilute-magnetic semiconductor (H, F, B), or ferro-magnetic-metal (Cl, Li) character in C2N monolayer. It was also found that the inclusion of hydrogen or oxygen impurities and nitrogen vacancies, can induce magnetism in the C2N monolayer. These extensive calculations can be useful to guide future studies to modify the electronic/optical properties of two-dimensional materials. (C) 2019 Elsevier Ltd. All rights reserved.

Abstract: Sub-monolayer control over the growth at silicon-oxide interfaces is a prerequisite for epitaxial integration of complex oxides with the Si platform, enriching it with a variety of functionalities. However, the control over this integration is hindered by the intense reaction of the constituents. The most suitable buffer material for Si passivation is metallic strontium. When it is overgrown with a layer of SrTiO3 (STO) it can serve as a pseudo-substrate for the integration with functional oxides. In our study we determined a mechanism for epitaxial integration of STO with a (1 x 2) + (2 x 1) reconstructed Sr(1/2 ML)/Si(001) surface using all-pulsed laser deposition (PLD) technology. A detailed analysis of the initial deposition parameters was performed, which enabled us to develop a complete protocol for integration, taking into account the peculiarities of the PLD growth, STO critical thickness, and process thermal budget, in order to kinetically trap the reaction between STO and Si and thus to minimize the thickness of the interface layer. The as-prepared oxide layer exhibits STO(001)8Si(001) out-of-plane and STO[110]8Si[100] in-plane orientation and together with recent advances in large-scale PLD tools these results represent a new technological solution for the implementation of oxide electronics on demand.

Abstract: It is important to understand the effect of the interfaces between the oxide electrode layers and the ferroelectric layer on the polarization response for optimizing the device performance of all-oxide ferroelectric devices. Herein, the effects of the oxide La0.07Ba0.93SnO3 (LBSO) as an electrode material in an PbZr0.52Ti0.48O3 (PZT) ferroelectric capacitor are compared with those of the more commonly used SrRuO3 (SRO) electrode. SRO (top)/PZT/SRO (bottom), SRO/PZT/LBSO, and SRO/PZT/2 nm SRO/LBSO devices are fabricated. Only marginal differences in crystalline properties, determined by X-ray diffraction and scanning transmission electron microscopy, are found. High-quality polarization loops are obtained, but with a much larger coercive field for the SRO/PZT/LBSO device. In contrast to the SRO/PZT/SRO device, the polarization decreases strongly with increasing field cycling. This fatigue problem can be remedied by inserting a 2 nm SRO layer between PZT and LBSO. It is argued that strongly increased charge injection into the PZT occurs at the bottom interface, because of the low PZT/LBSO interfacial barrier and the much lower carrier density in LBSO, as compared with that in SRO, causing a low dielectric constant, depleted layer in LBSO. The charge injection creates a trapped space charge in the PZT, causing the difference in fatigue behavior.

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: First-principles calculations have been carried out to investigate the stability, structural and electronic properties of two-dimensional (2D) hydrogenated GaAs with three possible geometries: chair, zigzag-line and boat configurations. The effect of van der Waals interactions on 2D H-GaAs systems has also been studied. These configurations were found to be energetic and dynamic stable, as well as having a semiconducting character. Although 2D GaAs adsorbed with H tends to form a zigzag-line configuration, the energy differences between chair, zigzag-line and boat are very small which implies the metastability of the system. Chair and boat configurations display a – direct bandgap nature, while pristine 2D-GaAs and zigzag-line are indirect semiconductors. The bandgap sizes of all configurations are also hydrogen dependent, and wider than that of pristine 2D-GaAs with both PBE and HSE functionals. Even though DFT-vdW interactions increase the adsorption energies and reduce the equilibrium distances of H-GaAs systems, it presents, qualitatively, the same physical results on the stability and electronic properties of our studied systems with PBE functional. According to our results, 2D buckled gallium arsenide is a good candidate to be synthesized by hydrogen surface passivation as its group III-V partners 2D buckled gallium nitride and boron nitride. The hydrogenation of 2D-GaAs tunes the bandgap of pristine 2D-GaAs, which makes it a potential candidate for optoelectronic applications in the blue and violet ranges of the visible electromagnetic spectrum.

Abstract: The irradiation of spherical gold nanoparticles (AuNPs) with nanosecond laser pulses induces shape transformations yielding nanocrystals with an inner cavity. The concentration of the stabilizing surfactant, the use of moderate pulse fluences, and the size of the irradiated AuNPs determine the efficiency of the process and the nature of the void. Hollow nanocrystals are obtained when molecules from the surrounding medium (e.g., water and organic matter derived from the surfactant) are trapped during laser pulse irradiation. These experimental observations suggest the existence of a subtle balance between the heating and cooling processes experienced by the nanocrystals, which induce their expansion and subsequent recrystallization keeping exogenous matter inside. The described approach provides valuable insight into the mechanism of interaction of pulsed nanosecond laser with AuNPs, along with interesting prospects for the development of hollow plasmonic nanoparticles with potential applications related to gas and liquid storage at the nanoscale.