Epitaxial growth of two-dimensional transition metal dichalcogenides on sapphire has emerged as a promising route to wafer-scale single-crystal films. Steps on the sapphire act as sites for transition metal dichalcogenide nucleation and can impart a preferred domain orientation, resulting in a substantial reduction in mirror twins. Here we demonstrate control of both the nucleation site and unidirectional growth direction of WSe2 on c-plane sapphire by metal–organic chemical vapour deposition. The unidirectional orientation is found to be intimately tied to growth conditions via changes in the sapphire surface chemistry that control the step edge location of WSe2 nucleation, imparting either a 0° or 60° orientation relative to the underlying sapphire lattice. The results provide insight into the role of surface chemistry on transition metal dichalcogenide nucleation and domain alignment and demonstrate the ability to engineer domain orientation over wafer-scale substrates.
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Additional data relevant to the conclusions of this study are available in the Supplementary Information. Growth and characterization data associated with the samples produced in this study are available via ScholarSphere52. This includes substrate preparation and recipe data for samples grown by MOCVD in the 2DCC-MIP facility and standard characterization data including AFM images, room-temperature Raman/photoluminescence spectra and field-emission scanning electron microscopy images of the samples. Videos associated with the DFT results are included as Supplementary Videos 1–8 and are available via figshare at https://doi.org/10.6084/m9.figshare.23274647 (ref. 53). Additional datasets related to DFT, SHG, TEM, FET and low-temperature photoluminescence are available from the corresponding author upon request.
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The work was financially supported by the National Science Foundation (NSF) through the Pennsylvania State University 2D Crystal Consortium–Materials Innovation Platform (2DCC-MIP) under NSF cooperative agreement numbers DMR-1539916 and DMR-2039351. S.B. and N.A. acknowledge support provided by NSF Career grant number DMR-1654107. T.V.M. and J.M.R. acknowledge support from the Defense Technical Information Center under award number FA9550-21-1-0460. N.T. acknowledges support from the NSF Graduate Research Fellowship Program under grant number DGE1255832. K.Z. and S.H. acknowledge support from NSF under grant numbers ECCS-1943895 and ECCS-2246564 and Air Force Office of Scientific Research under grant number FA9550-22-1-0408. SHG measurements were supported by the Center for Nanophase Materials Sciences (CNMS), which is a US Department of Energy Office of Science User Facility at Oak Ridge National Laboratory.
The authors declare no competing interests.
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Supplementary Figs. 1–26 and Discussion.
Nucleation of a TRIANGULAR WSe2 on the BOTTOM terrace of a MIXED Se/O step.
Nucleation of a TRIANGULAR WSe2 on the TOP terrace of a MIXED Se/O step.
Nucleation of a TRIANGULAR WSe2 on the BOTTOM terrace of a SINGLE Se step.
Nucleation of a TRIANGULAR WSe2 on the TOP terrace of a SINGLE Se step.
Nucleation of a RIBBON WSe2 on the BOTTOM terrace of a MIXED Se/O step.
Nucleation of a RIBBON WSe2 on the TOP terrace of a MIXED Se/O step.
Nucleation of a RIBBON WSe2 on the BOTTOM terrace of a SINGLE Se step.
Nucleation of a RIBBON WSe2 on the TOP terrace of a SINGLE Se step.
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Zhu, H., Nayir, N., Choudhury, T.H. et al. Step engineering for nucleation and domain orientation control in WSe2 epitaxy on c-plane sapphire. Nat. Nanotechnol. 18, 1295–1302 (2023). https://doi.org/10.1038/s41565-023-01456-6
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