Surface Magnetism in Pristine α Rhombohedral Boron and Intersurface Exchange Coupling Mechanism of Boron Icosahedra

Magnetic semiconducting borophenes and their derivatives

Two semiconducting borophenes with layer-dependent magnetism are predicted based on spin-polarized density functional theory. Both monolayer borophenes are ferromagnetic. One is composed of B3 and B15 triangular motifs, exhibiting bipolar spin polarization and a magnetic moment of 1.00 μB per primitive cell. The other consists of B15 triangular motifs, possessing a Curie temperature of about 437 K and a magnetic moment of 3.00 μB per primitive cell. B atoms located between the triangular motifs are essential for inducing ferromagnetism in monolayer borophenes. However, bilayer borophenes with high-symmetry stacking orders are nonmagnetic. Furthermore, magnetic boron nanotubes and fullerenes could be made of monolayer borophenes. Finally, we propose to fabricate these magnetic semiconducting borophenes from the buckled triangular structure of borophenes via selective electron beam ionization of B atoms by scanning transmission electron microscopy.

A new type of stable borophene with flat-band-induced magnetism

Based on first-principles calculations, we propose a new type of thermally and dynamically stable magnetic borophene (B11) with a tetragonal lattice. The magnetism is found coming from spin polarization of one bonding flat band located at the Fermi level. Despite of the 'anti-molecular' behavior in the monolayer, the interactions between thepzorbitals of the B atoms in the double-octahedron structural unit lead to the formation of the flat bands with localization behaviors. One tight binding model is built to comprehend the magnetic mechanism, which can guide us to tune other nonmagnetic borophene becoming magnetic. Biaxial tensile strain (>2.1%) is found triggering a phase transition from a semimetal to a semiconductor in the B11monolayer. The mechanism is analyzed based on the orbital-resolved crystal field effect. Our work provides a new route for designing and achieving two-dimensional magnetic materials with light elements.

Surface Damage Coupling Mechanism of Plain Weave Art Ceramic Matrix Composites

In order to solve the problem of the surface damage coupling mechanism of ceramic matrix composites, a method oriented to the damage coupling mechanism of the plain weave art ceramic matrix is proposed by the author. First, the author uses the composite material prepared by a chemical vapor infiltration process as the research object, and the damage mechanical behavior of materials under simple and complex plane stress states is studied. Second, the calculation of the mechanical property parameters of the material components and the research on the mechanical behavior of the material in-plane shear mesodamage are studied; Finally, the research on the damage coupling effect of materials under complex stress state is conducted, as well as the decoupling test research of the damage coupling effect. It is demonstrated that based on 0 and 45° off-axis tensile stress-strain behavior, a prediction model of off-axis tensile stress-strain behavior of the material was established, and the prediction results were in good agreement with the experimental results.