Reliable and controllable synthesis of two-dimensional (2D) hexagonal boron nitride (h-BN) layers is highly desirable for their applications as 2D dielectric and wide bandgap semiconductors. In this work, we demonstrate that the dissolution of carbon into cobalt (Co) and nickel (Ni) substrates can facilitate the growth of h-BN and attain large-area 2D homogeneity. The morphology of the h-BN film can be controlled from 2D layer-plus-3D islands to homogeneous 2D few-layers by tuning the carbon interstitial concentration in the Co substrate through a carburization process prior to the h-BN growth step. Comprehensive characterizations were performed to evaluate structural, electrical, optical, and dielectric properties of these samples. Single-crystal h-BN flakes with an edge length of ∼600 μm were demonstrated on carburized Ni. An average breakdown electric field of 9 MV/cm was achieved for an as-grown continuous 3-layer h-BN on carburized Co. Density functional theory calculations reveal that the interstitial carbon atoms can increase the adsorption energy of B and N atoms on the Co(111) surface and decrease the diffusion activation energy and, in turn, promote the nucleation and growth of 2D h-BN.

The outstanding physical properties of two dimensional (2D) materials have sparked continuous research interest in exploiting these materials for next generation high-performance electronic and photonic technology. Scalable synthesis of high-quality large-area 2D hexagonal boron nitride (h-BN)

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The singular density of states and the two Fermi wavevectors resulting from a ring-shaped or "Mexican hat" valence band give rise to unique trends in the charged impurity scattering rates and charged impurity limited mobilities. Ring shaped valence bands are common features of many monolayer and few-layer two-dimensional materials including the III-VI materials GaS, GaSe, InS, and InSe. The wavevector dependence of the screening, calculated within the random phase approximation, is so strong that it is the dominant factor determining the overall trends of the scattering rates and mobilities with respect to temperature and hole density. Charged impurities placed on the substrate and in the 2D channel are considered. The different wavevector dependencies of the bare Coulomb potentials alter the temperature dependence of the mobilities. Moving the charged impurities 5Å from the center of the channel to the substrate increases the mobility by an order of magnitude.

Two-dimensional (2D) hexagonal boron nitride (h-BN) plays a significant role in nanoscale electrical and optical devices because of its superior properties. However, the difficulties in the controllable growth of high-quality films hinder its applications. One of the crucial factors that influence the quality of the films obtained via epitaxy is the substrate property. Here, we report a study of 2D h-BN growth on carburized Ni substrates using molecular beam epitaxy. It was found that the carburization of Ni substrates with different surface orientations leads to different kinetics of h-BN growth. While the carburization of Ni(100) enhances the h-BN growth, the speed of the h-BN growth on carburized Ni(111) reduces. As-grown continuous single-layer h-BN films are used to fabricate Ni/h-BN/Ni metal–insulator–metal (MIM) devices, which demonstrate a high breakdown electric field of 12.9 MV/cm.

Control of the Néel vector in antiferromagnetic materials is one of the challenges preventing their use as active device components. Several methods have been investigated such as exchange bias, electric current, and spin injection, but little is known about strain-mediated anisotropy. This study of the antiferromagnetic L1 0 -type MnX alloys MnIr, MnRh, MnNi, MnPd, and MnPt shows that a small amount of strain effectively rotates the direction of the Néel vector by 90 • for all of the materials. For MnIr, MnRh, MnNi, and MnPd, the Néel vector rotates within the basal plane. For MnPt, the Néel vector rotates from out-of-plane to in-plane under tensile strain. The effectiveness of strain control is quantified by a metric of efficiency and by direct calculation of the magnetostriction coefficients. The values of the magnetostriction coefficients are comparable with those from ferromagnetic materials. These results indicate that strain is a mechanism that can be exploited for control of the Néel vectors in this family of antiferromagnets.

The controlled tunability of superconductivity in low-dimensional materials may enable new quantum devices. Particularly in triplet or topological superconductors, tunneling devices such as Josephson junctions, etc., can demonstrate exotic functionalities. The tunnel barrier, an insulating or normal material layer separating two superconductors, is a key component for the junctions. Thin layers of NbSe2 have been shown as a superconductor with strong spin orbit coupling, which can give rise to topological superconductivity if driven by a large magnetic exchange field. Here we demonstrate the superconductor–insulator transitions in epitaxially grown few-layer NbSe2 with wafer-scale uniformity on insulating substrates. We provide the electrical transport, Raman spectroscopy, cross-sectional transmission electron microscopy, and X-ray diffraction characterizations of the insulating phase. We show that the superconductor–insulator transition is driven by strain, which also causes characteristic energy shifts of the Raman modes. Our observation paves the way for high-quality heterojunction tunnel barriers to be seamlessly built into epitaxial NbSe2 itself, thereby enabling highly scalable tunneling devices for superconductor-based quantum electronics.

We present example applications of an approach to high-throughput first-principles calculations of the electronic properties of materials implemented within the Exabyte.io platform 1,2 . We deploy computational techniques based on the Density Functional Theory with both Generalized Gradient Approximation (GGA) and Hybrid Screened Exchange (HSE) in order to extract the electronic band gaps and band structures for a set of 775 binary compounds. We find that for HSE, the average relative error fits within 22%, whereas for GGA it is 49%. We find the average calculation time on an up-to-date server centrally available from a public cloud provider to fit within 1.2 and 36 hours for GGA and HSE, respectively. The results and the associated data, including the materials and simulation workflows, are standardized and made available online in an accessible, repeatable and extensible setting. arXiv:1808.05325v1 [cond-mat.mtrl-sci]