Isotopic phonon effects in β-rhombohedral boron--non-statistical isotope distribution

Few-Layer Borophene Prepared by Mechanical Resonance and Its Application in Terahertz Shielding

Once two-dimensional boron-based materials were forecasted, their excellent physical and chemical properties have realized attractive application value in the field of materials science. However, borophene could not exist independently and stably in nature. Molecular beam epitaxy is the only way being used currently for the preparation of borophene, which has low yield and harsh experimental installation conditions. Here, we propose the theory that few-layer borophene supported by silver nanoparticles can exist stably and large-scale preparation of few-layer borophene can be performed by mechanical resonance first. We have revealed that the structure of the prepared borophene is α-sheet and its thickness is less than 4 nm. The oxidation rate of borophene from the experiment is about 0.19, which indicates that the few-layer borophene possesses good structure stability. We have also studied the structure stability of borophene on silver nanoparticles by first principles calculation. The calculation proves that few-layer borophene can exist stably supported with silver nanoparticles. Furthermore, the terahertz shielding and stealth performance of the few-layer borophene have been explored. The maximum terahertz shielding effectiveness value of the prepared material could reach up to 50 and 21.5 dB for the reflection loss value in the broadband range of 0.1-2.7 THz. The large-scale preparation of few-layer borophene through the mechanical method makes it possible to study the properties of borophene and achieve low-cost large-scale applications, such as the study of terahertz shielding and stealth performance in the article, which facilitates the lightweight material design for terahertz shielding and stealth.

Structure of superhard tungsten tetraboride: a missing link between MB2 and MB12 higher borides

Superhard metals are of interest as possible replacements with enhanced properties over the metal carbides commonly used in cutting, drilling, and wear-resistant tooling. Of the superhard metals, the highest boride of tungsten--often referred to as WB4 and sometimes as W(1-x)B3--is one of the most promising candidates. The structure of this boride, however, has never been fully resolved, despite the fact that it was discovered in 1961--a fact that severely limits our understanding of its structure-property relationships and has generated increasing controversy in the literature. Here, we present a new crystallographic model of this compound based on refinement against time-of-flight neutron diffraction data. Contrary to previous X-ray-only structural refinements, there is strong evidence for the presence of interstitial arrangements of boron atoms and polyhedral bonding. The formation of these polyhedral--slightly distorted boron cuboctahedra--appears to be dependent upon the defective nature of the tungsten-deficient metal sublattice. This previously unidentified structure type has an intermediary relationship between MB2 and MB12 type boride polymorphs. Manipulation of the fractionally occupied metal and boron sites may provide insight for the rational design of new superhard metals.