Gang Ni

Stability and strength of atomically thin borophene from first principles calculations

ABSTRACT A new 2D material, borophene, has been grown successfully recently on single crystal Ag substrates. Three main structures have been proposed (, and striped borophene). However, the stability of three structures is still in debate. Using first principles calculations, we examine the dynamical, thermodynamical and mechanical stability of , and striped borophene. Free-standing and borophene is dynamically, thermodynamically and mechanically stable, while striped borophene is dynamically and thermodynamically unstable due to high stiffness along a direction. The origin of high stiffness and high instability in striped borophene along a direction can both be attributed to strong directional bonding. Our work shows a deep connection between stability and strength, and helps researchers to estimate accurately the mechanical performance of 2D materials. GRAPHICAL ABSTRACT IMPACT STATEMENT A benchmark for examining the relative stability of different structures of borophene is provided. Strong directional bonding in striped borophene leads to high stiffness and high brittleness.

Phonon transport properties of two-dimensional group-IV materials from ab initio calculations

materials from ab initio Bo Peng1, Hao Zhang1,∗, Hezhu Shao2, Yuanfeng Xu1, Gang Ni1, Rongjun Zhang1 and Heyuan Zhu1 1Shanghai Ultra-precision Optical Manufacturing Engineering Research Center and Key Laboratory of Micro and Nano Photonic Structures (Ministry of Education), Department of Optical Science and Engineering, Fudan University, Shanghai 200433, China 2Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Ningbo 315201, China

First-principles study on the electronic, optical, and transport properties of monolayer α - and β -GeSe

Yuanfeng Xu1, Hao Zhang1,4,†, Hezhu Shao2, Gang Ni1, Hongliang Lu3, Rongjun Zhang1, Bo Peng1, Yongyuan Zhu4 and Heyuan Zhu1,‡ 1Department of Optical Science and Engineering and Key Laboratory of Micro and Nano Photonic Structures (Ministry of Education), Fudan University, Shanghai 200433, China 2Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Ningbo 315201, China 3State Key Laboratory of ASIC and System, Institute of Advanced Nanodevices,School of Microelectronics, Fudan University, Shanghai 200433, China 4Nanjing University, National Laboratory of Solid State Microstructure, Nanjing 210093, China∗

Chemical intuition for high thermoelectric performance in monolayer black phosphorus, α-arsenene and aW-antimonene

Identifying materials with intrinsically high thermoelectric performance remains a challenge even with the aid of a high-throughput search. Here, using a chemically intuitive approach based on the bond-orbital theory, three anisotropic 2D group-V materials (monolayer black phosphorus, α-arsenene, and aW-antimonene) are identified as candidates for high thermoelectric energy conversion efficiency. Concepts, such as bond length, bond angle, and bond strength, are used to explain the trends in their electronic properties, such as the band gap and the effective mass. Our first principles calculations confirm that high carrier mobilities and large Seebeck coefficients can be obtained at the same time in these materials, due to complex Fermi surfaces originating from the anisotropic structures. An intuitive understanding of how the bonding character affects phonon transport is also provided with emphasis on the importance of bonding strength and bond anharmonicity. High thermoelectric performance is observed in these materials. Our approach provides a powerful tool to identify new thermoelectric materials and evaluate their transport properties.

Anisotropic ultrahigh hole mobility in two-dimensional penta-SiC2 by strain-engineering: electronic structure and chemical bonding analysis

Monolayer pentagonal silicon dicarbide is a 2D material composed entirely of pentagons, and it possesses novel electronic properties possibly leading to many potential applications. In this paper, using first-principles calculations, we have systematically investigated the electronic, mechanical and transport properties of monolayer penta-SiC2 by strain-engineering. By applying in-plane tensile or compressive strain, it is possible to modulate the physical properties of monolayer penta-SiC2, which subsequently changes the transport behaviour of the carriers. More interestingly, at room temperature, the uniaxial compressive strain of −8% along the a-direction can enhance the hole mobility of monolayer penta-SiC2 along the b-direction by almost three orders of magnitude up to 1.14 × 106 cm2 V−1 s−1, which is much larger than that of graphene, while similar strains have little influence on the electron mobility. The ultrahigh and strain-modulated carrier mobility in monolayer penta-SiC2 may lead to many novel applications in high-performance electronic and optoelectronic devices.