Dendritic patterns mediated by non-equilibrium growth processes are ubiquitous in all length scales from atomic metal islands [ 1 ] to macroscopic snowfl akes. [ 2 ] These fractal species have attracted great research interests regarding their complex morphologies, unique formation mechanisms, [ 3 ] and more importantly intriguing physical and chemical properties. [ 4 ] A model fractal growth system toward these is metal-on-metal epitaxy [ 5 ] which is usually mediated by a limited diffusion of adatoms along island edges with respect to that on free surfaces, following a diffusion-limited aggregation (DLA) mechanism. [ 6 ] Notably, adatoms in this model have to hop among predefi ned lattice sites of the substrate to achieve effi cient bonding, [ 7 ] and the resultant epilayer usually follows the same lattice symmetry as that of the substrate. However, it remains an open question what would happen if the symmetry of the overlayer differs from that of the substrate. Recently, it is intriguing to see that van der Waals epitaxial growth of compact 2D atomic crystals can be realized on symmetry-different metal substrates (e.g., graphene grown on Cu(001) [ 8 ] ). In this regard, it is imperative to know if the fl ake shape of similar 2D layered materials could be tailored from compact to fractal by the deliberately introduced adlayer-substrate symmetry disparity.Monolayer molybdenum disulfi de (MoS 2 ) has emerged as a star material due to its exceptional electronic [ 9 ] and optoelectronic [ 10 ] properties among the 2D crystal family. Particularly, in recent works, MoS 2 with rich active edges was proved to be an effi cient catalyst in electrochemical hydrogen evolution, [ 11 ] petrochemical hydrodesulfurization, [ 12 ] etc. However, dendritic MoS 2 samples were rarely achieved through chemical vapor deposition (CVD) or any other bottom-up synthesis methods, [ 13 ] with respect to that of the universally derived compact MoS 2 triangles.Herein, we realized the controllable synthesis of 2H-phase monolayer MoS 2 dendrites on a symmetry-disparate SrTiO 3 (STO) (001) substrate via a facile CVD method. With a combination of various characterization techniques, we tried to uncover the coverage-dependent fractal dimension, the crystallinity inside a dendritic fl ake, and fi nally the key factors that induce the dendritic growth behavior. It is expected that the Dendritic patterns generated in non-equilibrium growth processes are prevalent in nature while their formation mechanisms are far from fully understood. Here, we report a coverage-dependent fractal degree evolution of monolayer 2H-MoS 2 dendrites synthesized on a symmetry-disparate substrate of SrTiO 3 (001). Surprisingly, various characterizations have revealed that the monolayer dendrites featured with orthogonal backbones are single crystalline, possessing both peculiar adlayer-substrate interaction and abnormal indirect bandgap on SrTiO 3 (001). Further theoretical calculations indicate that a prominent diffusion anisotropy of monomer precursors, combined w...
Monolayer molybdenum disulfide (MoS2) has recently attracted intense interests due to its remarkable optical properties of valley-selected optical response, strong nonlinear wave mixing and photocurrent/photovoltaic generation and many corresponding potential applications. However, the nature of atomic-thin thickness of monolayer MoS2 leads to inefficient light-matter interactions and thereby hinders its optoelectronic applications. Here we report on the enhanced and controllable photo-response in MoS2 by utilizing surface plasmonic resonance based on metallic nano-antenna with characteristic lateral size of 40 × 80 nm. Our nano-antenna is designed to have one plasmonic resonance in the visible range and can enhance the MoS2 photoluminescence intensity up to 10 folds. The intensity enhancement can be effectively tuned simply by the manipulation of incident light polarization. In addition, we can also control the oscillator strength ratio between exciton and trion states by controlling polarization dependent hot carrier doping in MoS2. Our results demonstrate the possibility in controlling the photo-response in broad two-dimensional materials by well-designed nano-antenna and facilitate its coming optoelectronic applications.
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