Browsing by Author "Hu, Zhili"

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    Near-equilibrium growth from borophene edges on silver
    (AAAS, 2019) Zhang, Zhuhua; Mannix, Andrew J.; Liu, Xiaolong; Hu, Zhili; Guisinger, Nathan P.; Hersam, Mark C.; Yakobson, Boris I.
    Two-dimensional boron, borophene, was realized in recent experiments but still lacks an adequate growth theory for guiding its controlled synthesis. Combining ab initio calculations and experimental characterization, we study edges and growth kinetics of borophene on Ag(111). In equilibrium, the borophene edges are distinctly reconstructed with exceptionally low energies, in contrast to those of other two-dimensional materials. Away from equilibrium, sequential docking of boron feeding species to the reconstructed edges tends to extend the given lattice out of numerous polymorphic structures. Furthermore, each edge can grow via multiple energy pathways of atomic row assembly due to variable boron-boron coordination. These pathways reveal different degrees of anisotropic growth kinetics, shaping borophene into diverse elongated hexagonal islands in agreement with experimental observations in terms of morphology as well as edge orientation and periodicity. These results further suggest that ultrathin borophene ribbons can be grown at low temperature and low boron chemical potential.
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    Strain tolerance of two-dimensional crystal growth on curved surfaces
    (AAAS, 2019) Wang, Kai; Puretzky, Alexander A.; Hu, Zhili; Srijanto, Bernadeta R.; Li, Xufan; Gupta, Nitant; Yu, Henry; Tian, Mengkun; Mahjouri-Samani, Masoud; Gao, Xiang; Oyedele, Akinola; Rouleau, Christopher M.; Eres, Gyula; Yakobson, Boris I.; Yoon, Mina; Xiao, Kai; Geohegan, David B.
    Two-dimensional (2D) crystal growth over substrate features is fundamentally guided by the Gauss-Bonnet theorem, which mandates that rigid, planar crystals cannot conform to surfaces with nonzero Gaussian curvature. Here, we reveal how topographic curvature of lithographically designed substrate features govern the strain and growth dynamics of triangular WS2 monolayer single crystals. Single crystals grow conformally without strain over deep trenches and other features with zero Gaussian curvature; however, features with nonzero Gaussian curvature can easily impart sufficient strain to initiate grain boundaries and fractured growth in different directions. Within a strain-tolerant regime, however, triangular single crystals can accommodate considerable (<1.1%) localized strain exerted by surface features that shift the bandgap up to 150 meV. Within this regime, the crystal growth accelerates in specific directions, which we describe using a growth model. These results present a previously unexplored strategy to strain-engineer the growth directions and optoelectronic properties of 2D crystals.