Bottom-Up Growth of Monolayer Honeycomb SiC.

The long theorized two-dimensional allotrope of SiC has remained elusive amid the exploration of graphenelike honeycomb structured monolayers. It is anticipated to possess a large direct band gap (2.5 eV), ambient stability, and chemical versatility. While sp^{2} bonding between silicon and carbon is energetically favorable, only disordered nanoflakes have been reported to date. Here we demonstrate large-area, bottom-up synthesis of monocrystalline, epitaxial monolayer honeycomb SiC atop ultrathin transition metal carbide films on SiC substrates. We find the 2D phase of SiC to be almost planar and stable at high temperatures, up to 1200 °C in vacuum. Interactions between the 2D-SiC and the transition metal carbide surface result in a Dirac-like feature in the electronic band structure, which in the case of a TaC substrate is strongly spin-split. Our findings represent the first step towards routine and tailored synthesis of 2D-SiC monolayers, and this novel heteroepitaxial system may find diverse applications ranging from photovoltaics to topological superconductivity.

Giant valley-Zeeman coupling in the surface layer of an intercalated transition metal dichalcogenide.

Spin-valley locking is ubiquitous among transition metal dichalcogenides with local or global inversion asymmetry, in turn stabilizing properties such as Ising superconductivity, and opening routes towards 'valleytronics'. The underlying valley-spin splitting is set by spin-orbit coupling but can be tuned via the application of external magnetic fields or through proximity coupling. However, only modest changes have been realized to date. Here, we investigate the electronic structure of the V-intercalated transition metal dichalcogenide V1/3NbS2 using microscopic-area spatially resolved and angle-resolved photoemission spectroscopy. Our measurements and corresponding density functional theory calculations reveal that the bulk magnetic order induces a giant valley-selective Ising coupling exceeding 50 meV in the surface NbS2 layer, equivalent to application of a ~250 T magnetic field. This energy scale is of comparable magnitude to the intrinsic spin-orbit splittings, and indicates how coupling of local magnetic moments to itinerant states of a transition metal dichalcogenide monolayer provides a powerful route to controlling their valley-spin splittings.

Morphological and mechanical characterisation of three-dimensional gyroid structures fabricated by electron beam melting for the use as a porous biomaterial.

Additive manufactured porous biomaterials based on triply periodic minimal surfaces (TPMS) are a highly discussed topic in the literature. With their unique properties in terms of open porosity, large surface area and surface curvature, they are considered to have bone mimicking properties and remarkable osteogenic potential. In this study, scaffolds of gyroid unit cells of different sizes consisting of a Ti6Al4V alloy were manufactured additively by electron beam melting (EBM). The scaffolds were analysed by micro-computed tomography (micro-CT) to determine their morphological characteristics and, subsequently, subjected to mechanical tests to investigate their quasi-static compressive properties and fatigue resistance. All scaffolds showed an average open porosity of 71-81%, with an average pore size of 0.64-1.41 mm, depending on the investigated design. The design with the smallest unit cell shows the highest quasi-elastic gradient (QEG) as well as the highest compressive offset stress and compression strength. Furthermore, the fatigue resistance of all unit cell size (UCS) variations showed promising results. In detail, the smallest unit cells achieved fatigue strength at 106 cycles at 45% of their compressive offset stress, which is comparatively good for additively manufactured porous biomaterials. In summary, it is demonstrated that the mechanical properties can be significantly modified by varying the unit cell size, thus enabling the scaffolds to be specifically tailored to avoid stress shielding and ensure implant safety. Together with the morphological properties of the gyroid unit cells, the fabricated scaffolds represent a promising approach for use as a bone substitute material.

Insight into the Temperature Evolution of Electronic Structure and Mechanism of Exchange Interaction in EuS.

Discovered in 1962, the divalent ferromagnetic semiconductor EuS (TC = 16.5 K, Eg = 1.65 eV) has remained constantly relevant to the engineering of novel magnetically active interfaces, heterostructures, and multilayer sequences and to combination with topological materials. Because detailed information on the electronic structure of EuS and, in particular, its evolution across TC is not well-represented in the literature but is essential for the development of new functional systems, the present work aims at filling this gap. Our angle-resolved photoemission measurements complemented with first-principles calculations demonstrate how the electronic structure of EuS evolves across a paramagnetic-ferromagnetic transition. Our results emphasize the importance of the strong Eu 4f-S 3p mixing for exchange-magnetic splittings of the sulfur-derived bands as well as coupling between f and d orbitals of neighboring Eu atoms to derive the value of TC accurately. The 4f-3p mixing facilitates the coupling between 4f and 5d orbitals of neighboring Eu atoms, which mainly governs the exchange interaction in EuS.

Metal-passivated PbS nanoparticles: fabrication and characterization.

Organic-shell-free PbS nanoparticles have been produced in the size range relevant for quantum-dot solar cells (QDSCs) by a vapor aggregation method involving magnetron reactive sputtering. This method creates a beam of free 5-10 nm particles in a vacuum. The dimensions of the particles were estimated after their deposition on a substrate by imaging them using ex situ SEM and HRTEM electron microscopy. The particle structure and chemical composition could be deduced "on the fly", prior to deposition, using X-ray photoelectron spectroscopy (XPS) with tunable synchrotron radiation. Our XPS results suggest that under certain conditions it is possible to fabricate particles with a semiconductor core and 1 to 2 monolayer shells of metallic lead. For this case the absolute energy of the highest occupied molecular orbital (HOMO) in PbS has been determined to be (5.0 ± 0.5) eV below the vacuum level. For such particles deposited on a substrate HRTEM has confirmed the XPS-based conclusions on the crystalline PbS structure of the semiconductor core. Absorption spectroscopy on the deposited film has given a value of ∼1 eV for the lowest exciton. Together with the valence XPS results this has allowed us to reconstruct the energy level scheme of the particles. The results obtained are discussed in the context of the properties of PbS QDSCs.

Observation of a topologically non-trivial surface state in half-Heusler PtLuSb (001) thin films.

The discovery of topological insulators, materials with bulk band gaps and protected cross-gap surface states in compounds such as Bi2Se3, has generated much interest in identifying topological surface states (TSSs) in other classes of materials. In particular, recent theoretical calculations suggest that TSSs may be found in half-Heusler ternary compounds. If experimentally realizable, this would provide a materials platform for entirely new heterostructure spintronic devices that make use of the structurally identical but electronically varied nature of Heusler compounds. Here we show the presence of a TSS in epitaxially grown thin films of the half-Heusler compound PtLuSb. Spin- and angle-resolved photoemission spectroscopy, complemented by theoretical calculations, reveals a surface state with linear dispersion and a helical tangential spin texture consistent with previous predictions. This experimental verification of topological behaviour is a significant step forward in establishing half-Heusler compounds as a viable material system for future spintronic devices.

Spin-valley locking in the normal state of a transition-metal dichalcogenide superconductor.

Metallic transition-metal dichalcogenides (TMDCs) are benchmark systems for studying and controlling intertwined electronic orders in solids, with superconductivity developing from a charge-density wave state. The interplay between such phases is thought to play a critical role in the unconventional superconductivity of cuprates, Fe-based and heavy-fermion systems, yet even for the more moderately-correlated TMDCs, their nature and origins have proved controversial. Here, we study a prototypical example, 2H-NbSe2, by spin- and angle-resolved photoemission and first-principles theory. We find that the normal state, from which its hallmark collective phases emerge, is characterized by quasiparticles whose spin is locked to their valley pseudospin. This results from a combination of strong spin-orbit interactions and local inversion symmetry breaking, while interlayer coupling further drives a rich three-dimensional momentum dependence of the underlying Fermi-surface spin texture. These findings necessitate a re-investigation of the nature of charge order and superconducting pairing in NbSe2 and related TMDCs.

Factors influencing early poult flip-overs in experimental populations of turkeys.

A large number of poults from a line (E) selected long-term for increased egg production were observed, in recent generations, to flip over during the week immediately after hatching. This condition, termed early poult flip-overs (EPF), is characterized by the poults falling on their back and being unable to right themselves without assistance. Poults that flip over more than once appear to lack neurological control, lying on their backs with their legs paddling. If handled, the affected poult moves its head laterally and after several seconds appears to go to sleep. When placed on litter, the poult has no sense of balance and falls to one side or the other and starts paddling its feet. Poults that flip over may also chirp loudly. Observations from previous years indicate that no bacterial infectious agent was associated with the EPF condition. Affected poults have increased mortality relative to normal poults that do not flip over. The objective of the present study was to evaluate the effects of inheritance, beak trimming, hatching time, genetic growth potential, and poult hydration on the incidence of EPF. The E line had a greater incidence of EPF than its randombred control line, indicating the possibility of a genetic basis for the condition. However, within the E line, the heritability, based on variation among full-sib families, of the occurrence of EPF (assuming that EPF is an all-or-none trait) was low, being 0.044 and 0.052 in 2 consecutive yr. The heritability of the number of days (out of five) a poult continued to flip over was somewhat higher [0.26+/-0.002 (SE)]. Genetic growth potential may influence incidence of EPF for, when the E line was crossed with a large-bodied experimental line selected for increased 16-wk BW, the frequency of EPF was reduced and BW at 13 d of age was increased in the cross relative to the pure E line even though poult weight was similar at hatching in the two genetic groups. In the E line, later hatching poults within a hatch had a greater incidence of EPF than those hatching earlier. Neither beak trimming with an electronic beak trimmer nor poult hydration influenced EPF.

Range and confinement rearing of four genetic lines of turkeys. 1. Effects on growth, mortality, and walking ability.

Line by environment interactions complicate interpretation of results from long-term selection experiments. To investigate the potential effects of such interactions, a study was conducted in which birds from four genetic lines were reared in two environments. Birds from four turkey lines were brooded in confinement housing. At 8 wk of age, half of the birds from each full-sib family were moved to a large range pen and the remainder were placed in a large confinement pen. Significant line by environment interactions were present only for walking ability scores of males. A general lack of significant line by environment interactions indicates that rearing environment of these lines may be altered without affecting interpretation of results from a selection experiment. In addition, the current randombred control lines continue to adequately serve as control populations for a long-term selection experiment.

Spontaneous autoimmune thyroiditis in chickens. I. Effects of bursal reconstitution.

Chicks from strains genetically susceptible or resistant to spontaneous autoimmune thyroiditis were neonatally treated with cyclophosphamide to induce lymphocytic depletion of the bursa of Fabricius. The subsequent bursal repopulation with B cells from donors matched at the major histocompatibility locus showed B cells to be intricately associated with the pathogenesis of spontaneous autoimmune thyroiditis, although they themselves did not carry the potential for initiation of the disease.

Genetic influences on spontaneous autoimmune thyroiditis in (CS X OS)F2 chickens.

Genetic effects on spontaneous autoimmune thyroiditis in chickens were assessed by measuring phenotypic symptoms, the titer of circulating antibody to thyroglobulin, and the pathological change in the thyroids of young chicks. One or more loci within the B complex (the major histocompatibility complex of the chicken) are responsible for the expression of autoimmunity, and evidence is provided for an interaction of the B haplotype with genes at other loci. The influence of the B complex component on genetic susceptibility is more visible in animals with limited susceptibility at other loci and becomes indistinguishable as the frequency of other genes determining thyroid autoimmunity increases.

Changes in relative aggressiveness and social dominance associated with selection for early egg production in chickens.

We tested the hypothesis that artificial selection for early reproductive performance of chickens kept under competitive conditions increases aggressiveness and social dominance. Two populations subjected to long-term selection for number of eggs laid before 40 weeks of age and the unselected control population from which they derived were used. Results generally supported the hypothesis but indicated that increased aggressiveness associated with such selection may characterize the adolescent period only. For one of the selected strains, rank for aggressiveness and social dominance between adolescence and full maturity was reversed, relative to the control population. Associations between increased aggressiveness (and social dominance) and decreased age at sexual maturity are discussed, along with implications as to the role of social status and reproductive performance when different genetic strains compete within flocks.