Density functional theory simulations of B K and N K NEXAFS spectra of h-BN/transition metal(111) interfaces

Arthropods in landfills and their accumulation potential for toxic elements: A review

Landfills, as a source of potentially toxic elements (PTEs), pose a threat to the environment and human health. A literature review was conducted to explore the diversity of arthropods inhabiting solid waste landfills, as well as on the bioaccumulation of PTEs by arthropods. This review presents scientific papers over the last 20 years. Their importance in landfill ecosystems has been the subject of research; however, the issue of the accumulation of compounds such as toxic elements is emphasized only in a few studies. The bioaccumulation of PTEs was studied for 10 arthropod species that founded in landfills: Orthomorpha coarctata and Trigoniulus corallinus (class Diplopoda), Armadillidium vulgare and Trachelipus rathkii (class Malacostraca), the 6 species of the class Insecta - Zonocerus variegatus, Anacanthotermes ochraceus, Macrotermes bellicosus, Austroaeschna inermis, Calathus fuscipes and Harpalus rubripes.

Growth mechanisms of monolayer hexagonal boron nitride (h-BN) on metal surfaces: theoretical perspectives

Two-dimensional hexagonal boron nitride (h-BN) has appeared as a promising material in diverse areas of applications, including as an excellent substrate for graphene devices, deep-ultraviolet emitters, and tunneling barriers, thanks to its outstanding stability, flat surface, and wide-bandgap. However, for achieving such exciting applications, controllable mass synthesis of high-quality and large-scale h-BN is a precondition. The synthesis of h-BN on metal surfaces using chemical vapor deposition (CVD) has been extensively studied, aiming to obtain large-scale and high-quality materials. The atomic-scale growth process, which is a prerequisite for rationally optimizing growth circumstances, is a key topic in these investigations. Although theoretical investigations on h-BN growth mechanisms are expected to reveal numerous new insights and understandings, different growth methods have completely dissimilar mechanisms, making theoretical research extremely challenging. In this article, we have summarized the recent cutting-edge theoretical research on the growth mechanisms of h-BN on different metal substrates. On the frequently utilized Cu substrate, h-BN development was shown to be more challenging than a simple adsorption-dehydrogenation-growth scenario. Controlling the number of surface layers is also an important challenge. Growth on the Ni surface is controlled by precipitation. An unusual reaction-limited aggregation growth behavior has been seen on interfaces having a significant lattice mismatch to h-BN. With intensive theoretical investigations employing advanced simulation approaches, further progress in understanding h-BN growth processes is predicted, paving the way for guided growth protocol design.

A Review of Scalable Hexagonal Boron Nitride (h-BN) Synthesis for Present and Future Applications

Hexagonal boron nitride (h-BN) is a layered inorganic synthetic crystal exhibiting high temperature stability and high thermal conductivity. As a ceramic material it has been widely used for thermal management, heat shielding, lubrication, and as a filler material for structural composites. Recent scientific advances in isolating atomically thin monolayers from layered van der Waals crystals to study their unique properties has propelled research interest in mono/few layered h-BN as a wide bandgap insulating support for nanoscale electronics, tunnel barriers, communications, neutron detectors, optics, sensing, novel separations, quantum emission from defects, among others. Realizing these futuristic applications hinges on scalable cost-effective high-quality h-BN synthesis. Here, the authors review scalable approaches of high-quality mono/multilayer h-BN synthesis, discuss the challenges and opportunities for each method, and contextualize their relevance to emerging applications. Maintaining a stoichiometric balance B:N = 1 as the atoms incorporate into the growing layered crystal and maintaining stacking order between layers during multi-layer synthesis emerge as some of the main challenges for h-BN synthesis and the development of processes to address these aspects can inform and guide the synthesis of other layered materials with more than one constituent element. Finally, the authors contextualize h-BN synthesis efforts along with quality requirements for emerging applications via a technological roadmap.

Effects of Multiple Local Environments on Electron Energy Loss Spectra of Epitaxial Perovskite Interfaces

The role of local chemical environments in the electron energy loss spectra of complex multiferroic oxides was studied using computational and experimental techniques. The evolution of the O K-edge across an interface between bismuth ferrite (BFO) and lanthanum strontium manganate (LSMO) was considered through spectral averaging over crystallographically equivalent positions to capture the periodicity of the local O environments. Computational techniques were used to investigate the contribution of individual atomic environments to the overall spectrum, and the role of doping and strain was considered. Chemical variation, even at the low level, was found to have a major impact on the spectral features, whereas strain only induced a small chemical shift to the edge onset energy. Through a combination of these methods, it was possible to explain experimentally observed effects such as spectral flattening near the interface as the combination of spectral responses from multiple local atomic environments.

Wafer-scale and selective-area growth of high-quality hexagonal boron nitride on Ni(111) by metal-organic chemical vapor deposition

We demonstrate wafer-scale growth of high-quality hexagonal boron nitride (h-BN) film on Ni(111) template using metal-organic chemical vapor deposition (MOCVD). Compared with inert sapphire substrate, the catalytic Ni(111) template facilitates a fast growth of high-quality h-BN film at the relatively low temperature of 1000 °C. Wafer-scale growth of a high-quality h-BN film with Raman E_2g peak full width at half maximum (FWHM) of 18~24 cm⁻¹ is achieved, which is to the extent of our knowledge the best reported for MOCVD. Systematic investigation of the microstructural and chemical characteristics of the MOCVD-grown h-BN films reveals a substantial difference in catalytic capability between the Ni(111) and sapphire surfaces that enables the selective-area growth of h-BN at pre-defined locations over a whole 2-inch wafer. These achievement and findings have advanced our understanding of the growth mechanism of h-BN by MOCVD and will contribute an important step toward scalable and controllable production of high-quality h-BN films for practical integrated two-dimensional materials-based systems and devices.

Structural and electronic properties of epitaxial multilayer h-BN on Ni(111) for spintronics applications

Hexagonal boron nitride (h-BN) is a promising material for implementation in spintronics due to a large band gap, low spin-orbit coupling, and a small lattice mismatch to graphene and to close-packed surfaces of fcc-Ni(111) and hcp-Co(0001). Epitaxial deposition of h-BN on ferromagnetic metals is aimed at small interface scattering of charge and spin carriers. We report on the controlled growth of h-BN/Ni(111) by means of molecular beam epitaxy (MBE). Structural and electronic properties of this system are investigated using cross-section transmission electron microscopy (TEM) and electron spectroscopies which confirm good agreement with the properties of bulk h-BN. The latter are also corroborated by density functional theory (DFT) calculations, revealing that the first h-BN layer at the interface to Ni is metallic. Our investigations demonstrate that MBE is a promising, versatile alternative to both the exfoliation approach and chemical vapour deposition of h-BN.