The discovery of a superhard P-type transparent semiconductor: Al2.69B50

Superhard semiconductors have been long sought after for electronic device applications enduring extreme conditions, such as astronautics, due to their intrinsic toughness, high thermal and chemical stability. Here, we report the superhard p-type semiconductor Al_2.69B₅₀ single crystal with the determined Vickers hardness of ∼40.5 GPa under the load of 0.49 N, which is one of the hardest semiconductor compounds that have been ever found. With the direct band gap of 2.3 eV, Al_2.69B₅₀ exhibits excellent optical transmittance (>90%), covering the visible range from 459 nm to 760 nm and part of the infrared range, and also shows the high intensity of the photon emission in the visible light. Al_2.69B₅₀ is very stable, thermally and chemically, with an ultra-low density of ∼2.52 g cm^-3, allowing for further extension of its applications. Such an assembly of various excellent properties within one material has great implication for high power electronic design and applications.

Motif based high-throughput structure prediction of superconducting monolayer titanium boride

Two-dimensional boron structures, due to their diverse properties, have attracted great attention because of their potential applications in nanoelectronic devices. A series of TiBn (2 ≤ n ≤ 13) monolayers are efficiently constructed through our motif based method and theoretically investigated through high-throughput first-principles calculations. The configurations are generated based on the motifs of boron dimeric/triangular/quadrilateral fragments and multi-coordinate titanium-centered boron molecular wheels. Besides previously reported TiB4 and TiB9 which were discovered by the global search method, we predict that high symmetry monolayer TiB7 (Cmmm), which is octa-coordinate titanium boride, is dynamically stable. The TiB7 monolayer is a BCS superconductor with a transition temperature Tc of up to 8.3 K. The motif based approach is proved to be efficient in searching stable structures with prior knowledge so that the potentially stable transition metal monolayers can be quickly constructed by using basic cluster motifs. As an efficient way of discovering materials, the method is easily extended to predict other types of materials which have common characteristic patterns in the structure.