Abstract: Recent experiments show that an atomic step on the surface of atomically thin metallic films can strongly affect electronic transport. Here we reveal multiple and versatile effects that such a surface step can have on superconductivity in ultrathin films. By solving the Bogoliubov-de Gennes equations self-consistently in this regime, where quantum confinement dominates the emergent physics, we show that the electronic structure is profoundly modified on the two sides of the step, as is the spatial distribution of the superconducting order parameter and its dependence on temperature and electronic gating. Furthermore, the surface step changes nontrivially the transport properties both in the proximity-induced superconducting pair correlations and the Josephson effect, depending on the step height. These results offer a new route to tailor superconducting circuits and design atomically thin heterojunctions made of one same material.

Abstract: The electron energy spectrum in monolayer-bilayer-monolayer and in bilayer-monolayer-bilayer graphene structures is investigated and the effects of a perpendicular magnetic field and electric bias are studied. Different types of monolayer-bilayer interfaces are considered as zigzag (ZZ) or armchair (AC) junctions which modify considerably the bulk Landau levels (LLs) when the spectra are plotted as a function of the center coordinate of the cyclotron orbit. Far away from the two interfaces, one obtains the well-known LLs for extended monolayer or bilayer graphene. The LL structure changes significantly at the two interfaces or junctions where the valley degeneracy is lifted for both types of junctions, especially when the distance between them is approximately equal to the magnetic length. Varying the nonuniform bias and the width of this junction-to-junction region in either structure strongly influence the resulting spectra. Significant differences exist between ZZ and AC junctions in both structures. The densities of states (DOSs) for unbiased structures are symmetric in energy whereas those for biased structures are asymmetric. An external bias creates interface LLs in the gaps between the LLs of the unbiased system in which the DOS can be quite small. Such a pattern of LLs can be probed by scanning tunneling microscopy.

Abstract: The energy spectrum and eigenstates of single-layer black phosphorus nanoribbons in the presence of a perpendicular magnetic field and an in-plane transverse electric field are investigated by means of a tight-binding method, and the effect of different types of edges is examined analytically. A description based on a continuum model is proposed using an expansion of the tight-binding model in the long-wavelength limit. Thewave functions corresponding to the flatband part of the spectrum are obtained analytically and are shown to agree well with the numerical results from the tight-binding method for both narrow (10 nm) and wide (100 nm) nanoribbons. Analytical expressions for the critical magnetic field at which Landau levels are formed and the ranges of wave numbers in the dispersionless flatband segments in the energy spectra are derived. We examine the evolution of the Landau levels when an in-plane lateral electric field is applied, and we determine analytically how the edge states shift withmagnetic field. For wider nanoribbons, the conductance is shown to have a characteristic staircase shape in combined magnetic and electric fields. Some of the stairs in zigzag and skewed armchair nanoribbons originate from edge states that are found in the band gap.

Abstract: Oxidative etching was used to produce gold seeds of different sizes and crystal habits. Following detailed characterization, the seeds were grown under different conditions. Our results bring new insights toward understanding the effect of size and crystallinity on the growth of anisotropic particles, whilst identifying guidelines for the optimisation of new synthetic protocols of predesigned seeds.

Abstract: <script type='text/javascript'>document.write(unpmarked('The crystal and defect structure of SnS crystals grown using chemical vapour deposition for application in electronic devices are investigated. The structural analysis shows the presence of two distinct crystal morphologies, that is thin flakes with lateral sizes up to 50 m and nanometer scale thickness, and much thicker but smaller crystallites. Both show similar Raman response associated with SnS. The structural analysis with transmission electron microscopy shows that the flakes are single crystals of -SnS with [010] normal to the substrate. Parallel with the surface of the flakes, lamellae with varying thickness of a new SnS phase are observed. High-resolution transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM), first-principles simulations (DFT) and nanobeam diffraction (NBD) techniques are employed to characterise this phase in detail. DFT results suggest that the phase is a strain stabilised \u0027 one grown epitaxially on the -SnS crystals. TEM analysis shows that the crystallites are also -SnS with generally the [010] direction orthogonal to the substrate. Contrary to the flakes the crystallites consist of two to four grains which are tilted up to 15 degrees relative to the substrate. The various grain boundary structures and twin relations are discussed. Under high-dose electron irradiation, the SnS structure is reduced and -Sn formed. It is shown that this damage only occurs for SnS in direct contact with SiO2. Lay description SnS is a p-type semiconductor, which has attracted significant interest for electronic devices due to its unique properties, low-toxicity and abundance of Sn in nature. Although in the past it has been most extensively studied as the absorber material in solar cells, it has recently garnered interest for application as a p-type two-dimensional semiconductor in nanoelectronic devices due to its anisotropic layered structure similar to the better known phosphorene. Tin sulphide can take the form of several phases and the electronic properties of the material depend strongly on its crystal structure. It is therefore crucial to study the crystal structure of the material in order to predict the electronic properties and gain insight into the growth mechanism. In this work, SnS crystals deposited using a chemical vapour deposition technique are investigated extensively for their crystal and defect structure using transmission electron microscopy (TEM) and related techniques. We find the presence of two distinct crystal morphologies, that is thin flakes with lateral sizes up to 50 m and nm scale thickness, and much thicker but smaller crystallites. The flakes are single crystals of -SnS and contain lamellae with varying thickness of a different phase which appear to be -SnS at first glance. High-resolution scanning transmission electron microscopy is used to characterise these lamellae where the annular bright field (ABF) mode better reveals the position of the sulphur columns. The sulphur columns in the lamellae are found to be shifted relative to the -SnS structure which indicates the formation of a new phase which is a distorted version of the phase which we tentatively refer to as \u0027-SnS. Simulations based on density functional theory (DFT) are used to model the interface and a similar shift of sulphur columns in the -SnS layer is observed which takes place as a result of strong interaction at the interface between the two phases resulting in strain transfer. Nanobeam electron diffraction (NBD) is used to map the lattice mismatch in the thickness of the flakes which reveals good in-plane matching and some expansion out-of-plane in the lamellae. Contrary to the flakes the crystallites are made solely of -SnS and consist of two to four grains which are tilted up to 15 degrees relative to the substrate. The various grain boundary structures and twin relations are discussed. At high electron doses, SnS is reduced to -Sn, however the damage occurs only for SnS in direct contact with SiO2.'));

Abstract: The implementation of nitritation/denitritation (Nit/DNit) as alternative to nitrification/denitrification (N/DN) is driven by operational cost savings, e.g. 1.0-1.8 EUR/ton slurry treated. However, as for any biological nitrogen removal process, Nit/DNit can emit the potent greenhouse gas nitrous oxide (N2O). Challenges remain in understanding formation mechanisms and in mitigating the emissions, particularly at a low ratio of organic carbon consumption to nitrogen removal (CODrem/N-rem). In this study, the centrate (centrifuge supernatant) from anaerobic co-digestion of pig slurry was treated in a sequencing batch reactor. The process removed approximately 100% of ammonium a satisfactory nitrogen loading rate (0.4 g N/L/d), with minimum nitrite and nitrate in the effluent. Substantial N2O emission (around 17% of the ammonium nitrogen loading) was observed at the baseline operational condition (dissolved oxygen, DO, levels averaged at 0.85 mg O-2/L; CODrem/N-rem of 2.8) with similar to 68% of the total emission contributed by nitritation. Emissions increased with higher nitrite accumulation and lower organic carbon to nitrogen ratio. Yet, higher DO levels (similar to 2.2 mg O-2/L) lowered the aerobic N2O emission and weakened the dependency on nitrite concentration, suggesting a shift in N2O production pathway. The most effective N2O mitigation strategy combined intermittent patterns of aeration, anoxic feeding and anoxic carbon dosage, decreasing emission by over 99% (down to similar to 0.12% of the ammonium nitrogen loading). Without anaerobic digestion, mitigated Nit/DNit decreases the operational carbon footprint with about 80% compared to N/DN. With anaerobic digestion included, about 4 times more carbon is sequestered. In conclusion, the low CODrem/N-rem feature of Nit/DNit no longer offsets its environmental sustainability provided the process is smartly operated. (c) 2017 Elsevier Ltd. All rights reserved.

Abstract: Organophosphate esters (OPEs) are ubiquitous contaminants with potentially hazardous effects on both the environment and human health. Knowledge about the soil sorption-desorption process of organic chemicals is important in order to understand their fate, mobility, and bioavailability, enabling an estimation to be made of possible risks to the environment and biota. The aim of this study was to use the batch equilibrium technique to evaluate the sorption-desorption behavior of seven OPEs (TCEP, TCPP, TBEP, TDCP, TBP, TPhP, and EHDP) in soils with distinctive characteristics (two unamended soils and a soil amended with sewage sludge). The equilibrium concentrations of the OPEs were determined by high performance liquid chromatography coupled to a triple quadrupole mass spectrometer (HPLC-MS/MS). All the compounds were sorbed by the soils, and soil organic carbon (OC) played an important role in this process. The sorption of the most soluble OPEs (TCEP, TCPP, and TBEP) depended on soil OC content, although desorption was 58.1%. The less water-soluble OPEs (TDCP, TBP, TPhP, and EHDP) recorded total sorption (100% for TPhP and EHDP) or very high sorption (34.9%) by all the soils and were not desorbed, which could be explained by their highly hydrophobic nature, as indicated by the logarithmic octanol/water partition coefficient (K-ow) values higher than 3.8, resulting in a high affinity for soil OC. The results of the sorption-desorption of the OPEs by soils with different characteristics highlighted the influence of these compounds' physicochemical properties and the content and nature of soil OC in this process.

Abstract: Using the tight-binding approach, we investigate the electronic properties of bilayer phosphorene (BLP) quantum dots (QDs) in the presence of perpendicular electric and magnetic fields. Since BLP consists of two coupled phosphorene layers, it is of interest to examine the layer-dependent electronic properties of BLP QDs, such as the electronic distributions over the two layers and the so-produced layer-polarization features, and to see how these properties are affected by the magnetic field and the bias potential. We find that in the absence of a bias potential only edge states are layer polarized while the bulk states are not, and the layer-polarization degree (LPD) of the unbiased edge states increases with increasing magnetic field. However, in the presence of a bias potential both the edge and bulk states are layer polarized, and the LPD of the bulk (edge) states depends strongly (weakly) on the interplay of the bias potential and the interlayer coupling. At high magnetic fields, applying a bias potential renders the bulk electrons in a BLP QD to be mainly distributed over the top or bottom layer, resulting in layer-polarized bulk Landau levels (LLs). In the presence of a large bias potential that can drive a semiconductor-to-semimetal transition in BLP, these bulk LLs exhibit different magnetic-field dependences, i.e., the zeroth LLs exhibit a linearlike dependence on the magnetic field while the other LLs exhibit a square-root-like dependence.

Abstract: La1-yCayFe0.5+x(Mg,Mo)(0.5-x)O3-delta oxides with the orthorhombic GdFeO3-type perovskite structure have been synthesized at 1573 K. Transmission electron microscopy study for selected samples shows the coexistence of domains of perovskite phases with ordered and disordered B-cations. Mossbauer spectroscopy studies performed at 300 K and 573 K show that while compositions with low Ca-content (La0.55Ca0.45Fe0.5Mg0.2625Mo0.2375O3-delta and La0.5Ca0.5Fe0.6Mg0.175Mo0.225O3-delta) are nearly oxygen stoichiometric, La0.2Ca0.8Fe0.5Mg0.2625Mo0.2375O3-delta is oxygen deficient with delta approximate to 0.15. Oxides are stable in reducing atmosphere (Ar/H-2, 8%) at 1173 K for 12 h. No additional phases have been observed at XRPD patterns of all studied perovskites and Ce1-xGdxO2-x/2 electrolyte mixtures treated at 1173-1373K, while Fe-rich compositions (x >= 0.1) react with Zr1-xYxO2-x/2 electrolyte above 1273 K. Dilatometry studies reveal that all samples show rather low thermal expansion coefficients (TECs) in air of 11.4-12.7 ppm K-1. In reducing atmosphere their TECs were found to increase up to 12.1-15.4 ppm K-1 due to chemical expansion effect. High-temperature electrical conductivity measurements in air and Ar/H-2 atmosphere show that the highest conductivity is observed for Fe- and Ca-rich compositions. Moderate values of electrical conductivity and TEC together with stability towards chemical interaction with typical SOFC electrolytes make novel Fe-containing perovskites promising electrode materials for symmetrical solid oxide fuel cell.

Abstract: We show that a carbon nanotube decorated with different types of charged metallic nanoparticles exhibits unusual two-dimensional vibrations when actuated by applied electric field. Such vibrations and diverse possible trajectories are not only fundamentally important but also have minimum two characteristic frequencies that can be directly linked back to the properties of the constituents in the considered nanoresonator. Namely, those frequencies and the maximal deflection during vibrations are very distinctively dependent on the geometry of the nanotube, the shape, element, mass and charge of the nanoparticle, and are vastly tunable by the applied electric field, revealing the unique sensing ability of devices made of molecular filaments and metallic nanoparticles.

Abstract: Organic municipal solid waste (OMSW) as a feedstock for energy recovery and material recycling offers the potential to reduce environmental impacts from energy production while displacing emission intensive waste management strategies such as landfills. This paper quantifies the environmental impact of anaerobic digestion of local, residual biomass. A life-cycle assessment was jointly performed for two scenarios for the biological treatment of local organic municipal solid waste and pig manure in the Netherlands. Scenario 1 was a separate treatment using anaerobic digestion, and Scenario 2 was a bio-refinery system that integrates anaerobic digestion of organic, municipal solid waste, and co digestion of pig manure and other organic co-substrates \. For both scenarios, electricity and heat are generated using a combined heat and power engine. The bio-refinery system (Scenario 2) contribution to climate change resulted in 0.16 Mt CO2 eq./yr, which is lower than the 0.17 Mt CO2 eq./yr of Scenario 1. Both scenarios are found to be beneficial with regard to resource depletion and human toxicity. The integration of organic waste and manure anaerobic digestion has no effect on acidification and terrestrial eutrophication impact categories, resulting in 43.59 AE eq. and 86.33 AE eq. for Scenario 1 and 43.58 AE eq. and 86.30 AE eq. for Scenario 2. Moreover, Scenario 2 yields 18% lower emissions than those from natural gas derived electricity in the Netherlands. The biorefinery system represents an opportunity to improve organic waste-management strategies, at the same time as reducing the environmental impact from energy production and the costs for surplus manure disposal by producing high-quality commodities that can be traded on the market. (C) 2017 Elsevier Ltd. All rights reserved.

Abstract: Synthetic methods that allow for the controlled design of well-defined Pt nanoparticles are highly desirable for fundamental catalysis research. In this work, we propose a strategy that allows precise and independent control of the Pt particle size and coverage. Our approach exploits the versatility of the atomic layer deposition (ALD) technique by combining two ALD processes for Pt using different reactants. The particle areal density is controlled by tailoring the number of ALD cycles using trimethyl(methylcyclopentadienyl) platinum and oxygen, while subsequent growth using the same Pt precursor in combination with nitrogen plasma allows for tuning of the particle size at the atomic level. The excellent control over the particle morphology is clearly demonstrated by means of in situ and ex situ X-ray fluorescence and grazing incidence small angle X-ray scattering experiments, providing information about the Pt loading, average particle dimensions, and mean center-to-center particle distance.

Abstract: In this contribution, we report a fundamental study of the factors that set the contact resistivity between metals and highly doped semiconductors. We investigate the case of n-type doped Si contacted with amorphous TiSi combining first-principles calculations with Non-Equilibrium Green functions transport simulations. The intrinsic contact resistivity is found to saturate at similar to 2x10(-10) Omega.cm(2) with the doping concentration and sets an intrinsic limit to the ultimate contact resistance achievable for n-doped Si vertical bar amorphous-TiSi. This limit arises from the intrinsic properties of the semiconductor and of the metal such as their electron effective masses and Fermi energies. We illustrate that, in this regime, contacting metals with a heavy electron effective mass helps reducing the interface intrinsic contact resistivity.

Abstract: <script type='text/javascript'>document.write(unpmarked('To realize spintronic devices based on topological insulators (TIs), well-defined interfaces between magnetic metals and TIs are required. Here, we characterize atomically precisely the interface between the 3d transition metal Fe and the TI Bi2Te3 at different stages of its formation. Using photoelectron diffraction and holography, we show that after deposition of up to 3 monolayers Fe on Bi2Te3 at room temperature, the Fe atoms are ordered at the interface despite the surface disorder revealed by our scanning-tunneling microscopy images. We find that Fe occupies two different sites: a hollow adatom deeply relaxed into the Bi2Te3 quintuple layers and an interstitial atom between the third (Te) and fourth (Bi) atomic layers. For both sites, our core-level photoemission spectra and density-functional theory calculations demonstrate simultaneous chemical bonding of Fe to both Te and Bi atoms. We further show that upon deposition of Fe up to a thickness of 20 nm, the Fe atoms penetrate deeper into the bulk forming a 2-5 nm interface layer containing FeTe. In addition, excessive Bi is pushed down into the bulk of Bi2Te3 leading to the formation of septuple layers of Bi3Te4 within a distance of similar to 25 nm from the interface. Controlling the magnetic properties of the complex interface structures revealed by our work will be of critical importance when optimizing the efficiency of spin injection in TI-based devices.'));

Abstract: <script type='text/javascript'>document.write(unpmarked('Quantum electrodynamics predicts that heavy atoms (Z \u003E Z(c) approximate to 170) will undergo the process of atomic collapse where electrons sink into the positron continuum and a new family of so-called collapsing states emerges. The relativistic electrons in graphene exhibit the same physics but at a much lower critical charge (Z(c) approximate to 1) which has made it possible to confirm this phenomenon experimentally. However, there exist conflicting predictions on the effect of a magnetic field on atomic collapse. These theoretical predictions are based on the continuum Dirac-Weyl equation, which does not have an exact analytical solution for the interplay of a supercritical Coulomb potential and the magnetic field. Approximative solutions have been proposed, but because the two effects compete on similar energy scales, the theoretical treatment varies depending on the regime which is being considered. These limitations are overcome here by starting from a tight-binding approach and computing exact numerical results. By avoiding special limit cases, we found a smooth evolution between the different regimes. We predict that the atomic collapse effect persists even after the magnetic field is activated and that the critical charge remains unchanged. We show that the atomic collapse regime is characterized: (1) by a series of Landau level anticrossings and (2) by the absence of root B scaling of the Landau levels with regard to magnetic field strength.'));