Browsing by Author "Li, Xufan"

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    Nickel particle–enabled width-controlled growth of bilayer molybdenum disulfide nanoribbons
    (AAAS, 2021) Li, Xufan; Li, Baichang; Lei, Jincheng; Bets, Ksenia V.; Sang, Xiahan; Okogbue, Emmanuel; Liu, Yang; Unocic, Raymond R.; Yakobson, Boris I.; Hone, James; Harutyunyan, Avetik R.
    Transition metal dichalcogenides exhibit a variety of electronic behaviors depending on the number of layers and width. Therefore, developing facile methods for their controllable synthesis is of central importance. We found that nickel nanoparticles promote both heterogeneous nucleation of the first layer of molybdenum disulfide and simultaneously catalyzes homoepitaxial tip growth of a second layer via a vapor-liquid-solid (VLS) mechanism, resulting in bilayer nanoribbons with width controlled by the nanoparticle diameter. Simulations further confirm the VLS growth mechanism toward nanoribbons and its orders of magnitude higher growth speed compared to the conventional noncatalytic growth of flakes. Width-dependent Coulomb blockade oscillation observed in the transfer characteristics of the nanoribbons at temperatures up to 60 K evidences the value of this proposed synthesis strategy for future nanoelectronics.
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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.