Strain-Directed Layer-By-Layer Epitaxy Toward van der Waals Homo- and Heterostructures

Abstract
Transition-metal dichalcogenide (TMDC) homo- and heterostacks hold tantalizing prospects for being integrated as active components in future van der Waals (vdW) electronics and optoelectronics. However, most TMDC homo- and heterostacks are created by onerous mechanical exfoliation, followed by a mixing-and-matching process. While versatile enough for pilot demonstrations, these strategies are clearly not scalable for practical technologies and widespread implementations. Here, we report a two-step epitaxy strategy that promotes the growth of second-layer TMDCs on the basal plane of the first TMDCs epilayer. The first-layer TMDCs are grown on substrates where the tensile strength can be tuned by the control of chemical environments. The succeeding epilayers then prefer to grow layer-by-layer on the highly tensile-strained first layers. The result is the growth of high-density TMDC homo (WSe2) bilayers and hetero (WSe2–MoS2) bilayers with an exceedingly high yield (>99% bilayers) and uniformity. A density functional theory simulation further sheds light on how strain engineering shifts the subsequent layer growth preference. Second-harmonic generation and high-angle annular dark-field scanning transmission electron microscopy collectively attest to the AB and AA′ stacking between the TMDC epi- and overlayers. The proposed strategy could be a versatile platform for synthesizing diverse arrays of vdW homo- and heterostacks, thus providing prospects for realizing large-scale and layer-controllable two-dimensional electronics.

Citation
Wan, Y., Huang, J.-K., Chuu, C.-P., Hsu, W.-T., Lee, C.-J., Aljarb, A., … Tung, V. (2021). Strain-Directed Layer-By-Layer Epitaxy Toward van der Waals Homo- and Heterostructures. ACS Materials Letters, 442–453. doi:10.1021/acsmaterialslett.0c00554

Acknowledgements
V.T. and L.-J.L. acknowledge the support from King Abdullah University of Science and Technology (KAUST) Office of Sponsored Research (OSR) under Award No. OSR-2018-CARF/CCF-3079. V.T. is grateful for the support from KAUST Catalysis Center. A.A. and M.-H.C. are supported by KAUST Solar Center. W.H.C. acknowledges the support from the Ministry of Science and Technology of Taiwan (MOST-108-2119-M-009-011-MY3, MOST-107-2112-M-009-024-MY3) and from the CEFMS of NCTU supported by the Ministry of Education of Taiwan. V.T. and Y.W. are indebted to the support from Core Lab in KAUST and the fruitful discussions in DFT with Dr. Z. Cao.

Publisher
American Chemical Society (ACS)

Journal
ACS Materials Letters

DOI
10.1021/acsmaterialslett.0c00554

Additional Links
https://pubs.acs.org/doi/10.1021/acsmaterialslett.0c00554

Permanent link to this record