Borophene, a theoretically proposed two-dimensional (2D) boron allotrope1,2,3, has attracted much attention4,5 as a candidate material platform for high-speed, transparent and flexible electronics6,7,8,9. It was recently synthesized, on Ag(111) substrates10,11, and studied by tunnelling and electron spectroscopy12. However, the exact crystal structure is still controversial, the nanometre-size single-crystal domains produced so far are too small for device fabrication and the structural tunability via substrate-dependent epitaxy is yet to be proven. We report on the synthesis of borophene monitored in situ by low-energy electron microscopy, diffraction and scanning tunnelling microscopy (STM) and modelled by ab initio theory. We resolved the crystal structure and phase diagram of borophene on Ag(111), but found that the domains remain nanoscale for all growth conditions. However, by growing borophene on Cu(111) surfaces, we obtained large single-crystal domains, up to 100 μm2 in size. The crystal structure is a novel triangular network with a concentration of hexagonal vacancies of η = 1/5. Our experimental data, together with first principles calculations, indicate charge-transfer coupling to the substrate without significant covalent bonding. Our work sets the stage for fabricating borophene-based devices and substantiates the idea of borophene as a model for development of artificial 2D materials.
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All the data generated and analysed during this study are included within this paper and the associated Supplementary Information.
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This research was supported by the US Department of Energy, Basic Energy Sciences, Materials Sciences and Engineering Division. R.W. and A.G. are supported by the Gordon and Betty Moore Foundation’s EPiQS Initiative through grant GBMF4410. I.K.D. acknowledges the support of a BNL Gertrude and Maurice Goldhaber Distinguished Fellowship. This research used resources of the Center for Functional Nanomaterials, which is a US DOE Office of Science Facility, at Brookhaven National Laboratory under contract no. DE-SC0012704. S.E. is supported by the National Science Foundation Graduate Research Fellowship through grant DGE-1122492. S.E and S.I.-B. thank the computing resources provided by the staff of the Yale University Faculty of Arts and Sciences High Performance Computing Center as well as NSF XSEDE resources via grant TG-MCA08X007.
The authors declare no competing interests.
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Inorganic Boron-Based Nanostructures: Synthesis, Optoelectronic Properties, and Prospective Applications
Physical Review B (2019)
Condensed Matter (2019)
Advanced Optical Materials (2019)
Nature Communications (2019)