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Monolayer semiconductors of group-VA elements (As, Sb, Bi) with graphenelike buckled structure offer a potential to achieve nanoscale electronic, optoelectronic and thermoelectric devices. Motivated by recently-fabricated Sb monolayer (antimonene), we systematically investigate the thermoelectric properties of β-As, Sb and Bi monolayers by combining the first-principles calculations and semiclassical Boltzmann transport theory. The generalized gradient approximation (GGA) plus spin-orbit coupling (SOC) is adopted for the electron part, and GGA is employed for the phonon part. It is found that SOC has important influences on their electronic structures, especially for Bi monolayer, which can induce observable SOC effects on electronic transport coefficients. More specifically, SOC not only has detrimental influences on electronic transport coefficients, but also produces enhanced effects. The calculated lattice thermal conductivity decreases gradually from As to Bi monolayer, and the corresponding room-temperature sheet thermal conductance is 161.10 WK −1 , 46.62 WK −1 and 16.02 WK −1 , which can be converted into common lattice thermal conductivity by dividing by the thickness of 2D material. The sheet thermal conductance of Bi monolayer is lower than one of other 2D materials, such as semiconducting transition-metal dichalcogenide monolayers and orthorhombic group IV-VI monolayers. A series of scattering time is employed to estimate the thermoelectric figure of merit ZT . It is found that the n-type doping has more excellent thermoelectric properties than p-type doping for As and Bi monolayer, while the comparative ZT between n-and p-type doping is observed in Bi monolayer. These results can stimulate further experimental works to open the new field for thermoelectric devices based on monolayer of group-VA elements.

Structural transformation and the variation in the band gap of (0001) AlN and GaN films as a function of equibiaxial in-plane strain are studied using the HSE06 range-separated hybrid functional. Although AlN and GaN under strain share the same structural transition from wurtzite to a graphitelike phase, their electronic properties are significantly different. Both wurtzite and graphitelike AlN under strain can display either direct or indirect band structures, whereas the band gap of wurtzite GaN is always direct and graphitelike GaN always indirect. Furthermore, it is more difficult for AlN than GaN to obtain the graphitelike semi-metallic phase. Our results for GaN support the conclusions obtained from standard density functional theory [Dong et al., Appl. Phys. Lett. 96, 202106 (2010)]

We predict new tungsten borides, some of which are promising hard materials that are expected to be stable in a wide range of conditions, according to the computed composition-temperature phase diagram. New boron-rich compound WB is predicted to be superhard, with a Vickers hardness of 45 GPa, to possess high fracture toughness of ∼4 MPa·m, and to be thermodynamically stable in a wide range of temperatures at ambient pressure. Temperature dependences of the mechanical properties of the boron-richest WB and WB phases were studied using quasiharmonic and anharmonic approximations. Our results suggest that WB remains a high-performance material even at very high temperatures.

Dental pulp is critical to maintain the vitality of a tooth. Regeneration of pulpo-dentinal complex is of great interest to treat pulpitis and pulp necrosis. In this study, through three-dimensional spheroid culture, a group of unique multipotent stem cells were identified from mouse dental papilla called multipotent dental pulp regenerative stem cells (MDPSCs). MDPSCs exhibited enhanced osteogenic/odontogenic differentiation capabilities and could form regenerative dentin and neurovascular-like structures that mimicked the native teeth in vivo. Further analysis revealed that CD24a was the bona fide marker for MDPSCs, and their expansion was highly dependent on the expression of a key transcriptional factor, Sp7. Last, CD24a+ cells could be detected in primary dental papilla in mice and human, suggesting that MDPSCs resided in their native niches. Together, our study has identified a previously unidentified group of multipotent pulp regenerative stem cells with defined molecular markers for the potential treatment of pulpitis and pulp necrosis.

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