Atomically thin half-van der Waals metals enabled by confinement heteroepitaxy

Abstract

Atomically thin two-dimensional (2D) metals may be key ingredients in next-generation quantum and optoelectronic devices. However, 2D metals must be stabilized against environmental degradation and integrated into heterostructure devices at the wafer scale. The high-energy interface between silicon carbide and epitaxial graphene provides an intriguing framework for stabilizing a diverse range of 2D metals. Here we demonstrate large-area, environmentally stable, single-crystal 2D gallium, indium and tin that are stabilized at the interface of epitaxial graphene and silicon carbide. The 2D metals are covalently bonded to SiC below but present a non-bonded interface to the graphene overlayer; that is, they are ‘half van der Waals’ metals with strong internal gradients in bonding character. These non-centrosymmetric 2D metals offer compelling opportunities for superconducting devices, topological phenomena and advanced optoelectronic properties. For example, the reported 2D Ga is a superconductor that combines six strongly coupled Ga-derived electron pockets with a large nearly free-electron Fermi surface that closely approaches the Dirac points of the graphene overlayer.

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Fig. 1: CHet with defect-engineered epitaxial graphene.
Fig. 2: Atomic structure of CHet-grown 2D metals.
Fig. 3: Electronic structure of CHet-grown 2D Ga.
Fig. 4: Superconductivity in 2D Ga grown via CHet.
Fig. 5: Theoretical calculations on heterostructures of graphene and 2D Ga.

Data availability

The data that support the findings of this study are available at 10.6084/m9.figshare.c.4830711 or from the authors on reasonable request. See author contributions for specific data sets.

Code availability

Code used for computational investigations presented in this manuscript is available at gitlab.com/QEF/q-e/tree/qe-6.3 (EPW v5.0.0, Quantum Espresso v6.3) and www.vasp.at (VASP).

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Acknowledgements

Funding for this work was provided by the Northrop Grumman Mission Systems’ University Research Program, Semiconductor Research Corporation Intel/Global Research Collaboration Fellowship Program, task 2741.001, National Science Foundation (NSF) CAREER Awards 1453924 and 1847811, the Chinese Scholarship Council, an Alfred P. Sloan Research Fellowship, NSF DMR-1708972 and 1808900, and the 2D Crystal Consortium NSF Materials Innovation Platform under cooperative agreement DMR-1539916. A portion of this research was conducted at the Center for Nanophase Materials Sciences, which is a DOE Office of Science User Facility, and at the Pennsylvania State University Materials Research Institute’s Material Characterization Laboratory. This research used resources of the Advanced Light Source, which is a DOE Office of Science User Facility under contract no. DE-AC02-05CH11231. We acknowledge Haiying Wang for help with STEM sample cross-section preparation via FIB; Vince Bojan, Nabil Bassim and Heshem Elsherif for help with AES; and Max Wetherington for Raman spectroscopy support.

Author information

N.B, B.B., Y.W., V.C. and J.A.R. wrote the paper with input from the co-authors. N.B. performed CHet and XPS characterization and assisted in the Raman spectroscopy and SEM characterization. B.B performed the Raman spectroscopy and SEM characterization and assisted in sample preparation and electrical characterization. Y.W. performed DFT modelling of graphene/Ga/SiC heterostructures in consultation with V.C. with input from J.Z., B.B., N.B. and J.A.R.; J.J. performed electrical measurements under the direction of C.Z.C. with input from B.B and J.Z.; R.K., A.B. and C.J. performed ARPES measurements under the direction of E.R.; N.N. performed graphene defect modelling under the direction of A.v.D.; and K.W. performed cross-sectional STEM imaging. M.K. and W.K. prepared the LEED instrument for EG/metal/SiC samples, and M.K. performed the LEED measurements. A.D.L.F.D. assisted with CHet and material characterization. C.D. and S.S. performed the EG synthesis under the direction of J.A.R.; J.S. assisted in XPS data analysis. M.F., Q.Z., G.Z. and A.P.L. performed the scanning probe characterization. Y.W.C. assisted with electrical measurements under the direction of J.Z.

Correspondence to Joshua A. Robinson.

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Briggs, N., Bersch, B., Wang, Y. et al. Atomically thin half-van der Waals metals enabled by confinement heteroepitaxy. Nat. Mater. (2020). https://doi.org/10.1038/s41563-020-0631-x

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