The spectrum of two-dimensional (2D) and layered materials ‘beyond graphene’ offers a remarkable platform to study new phenomena in condensed matter physics. Among these materials, layered hexagonal boron nitride (hBN), with its wide bandgap energy (∼5.0–6.0 eV), has clearly established that 2D nitrides are key to advancing 2D devices1. A gap, however, remains between the theoretical prediction of 2D nitrides ‘beyond hBN’2,3 and experimental realization of such structures. Here we demonstrate the synthesis of 2D gallium nitride (GaN) via a migration-enhanced encapsulated growth (MEEG) technique utilizing epitaxial graphene. We theoretically predict and experimentally validate that the atomic structure of 2D GaN grown via MEEG is notably different from reported theory2,3,4. Moreover, we establish that graphene plays a critical role in stabilizing the direct-bandgap (nearly 5.0 eV), 2D buckled structure. Our results provide a foundation for discovery and stabilization of 2D nitrides that are difficult to prepare via traditional synthesis.
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Materials and experimental methods in this work were partially supported by Asahi Glass Japan and the National Science Foundation under grant numbers DMR-1006763 (J.M.R.), DMR-1410765 (J.M.R.), DMR-1420620 (J.M.R & J.A.R Seed Program through Penn State MRSEC—Center for Nanoscale Science) and DMR-1453924 (J.A.R.). Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation. Material characterization described in this work was supported by The Pennsylvania State University (PSU) Materials Characterization Laboratory (MCL) Staff Innovation Funding (SIF) Program, and the Alfred P. Sloan Foundation, USA. Theoretical work (S.D.) and XPS analysis (R.M.W.) was supported by the Center for Low Energy Systems Technology (LEAST). LEAST is one of six Semiconductor Research Corporation STARnet centres sponsored by MARCO and DARPA. We would like acknowledge V. Bojan (staff scientist, MCL) and J. Maier (technical staff, MCL) for contributions in AES analysis and FIB-TEM specimen preparation, respectively. In addition, we also acknowledge the microscopy and spectroscopy assistance provided by: N. Alem (PSU); K. Bernd (PSU); A. Azizi (PSU); J. Tischler (NRL); C. Ellis (NRL); J. Owrutsky (NRL) and T. Miyagi (Asahi Glass, Japan). Finally, we thank T. Tiwald (J.A. Woolam) for his assistance in developing the ellipsometric model with J.D.C. and P. Sheehan (NRL) for his beneficence in allowing us to use his ellipsometer.
The authors declare no competing financial interests.
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Al Balushi, Z., Wang, K., Ghosh, R. et al. Two-dimensional gallium nitride realized via graphene encapsulation. Nature Mater 15, 1166–1171 (2016). https://doi.org/10.1038/nmat4742
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