Assessing the Electronics of 2D Heterostructures—Stacked, Joined, Nested or Shaped to a Topography

For the materials’ hetero-bilayers, their chemical content, the shapes and mutual positioning of the parts—all create a multi-dimensional, multi-parametric, a space immensely large for any routine point-by-point assessment. Nevertheless, physical intuitive models equipped with quantitative DFT-based computing, can probe at least its sparse subset finding many examples of interest, where new physics and eventually device-functionality can emerge. Among the planar stacked van der Waals hetero-bilayers, (i) one can find pairs where valence and conductance bands nearly overlap (broken type-III gap), to reach realization of early Mott musings on the excitonic ground states and, accordingly, various possibilities of the condensate [1], with different electron-hole phases. (ii) If one layer is ferroelectric, its polarization can shift bands positions, allowing the spin-orbit coupling (SOC) to cause the band inversion, and thus switch the topological state [2], between trivial and nontrivial—eventually leading to possibility of reconfigurable 2D circuits. (iii) “Hetero” does break the symmetry and for heavy-elements containing layers with SOC, it can yield a surprising spin-split of electronic bands, the Rashba effect, coveted for spintronics. Its strength correlates with Born effective charges of frontier interface atoms, and further Pauling’s electronegativity of their pseudobond [3]. (iv) A dilemma for the future electronics, which of the contacts, top-stacked (no Fermi level pinning yet highly resistive) or coplanar edge-edge (well-bonded, less resistive but prone to Bardeen states and suppressed FLP, [4])—which type should dominate the future devices? We may further discus (v) cylindrical-coaxial hetero-structures of nested nanotubes [5], an architecture strikingly appealing for GAA FET, while already showing computed band offsets optimal for photovoltaic charge separation [6]. From our recent explorations, we learn how (vi) topography curvature induces symmetry-breaking flexoelectric field, enabling Rashba effect in TMD with heavy-elements [7] or (vii) creates, in undulated bilayer hBN, an array of 1D-flat bands [8] akin to the quantum wells, with no need for complex chemical-composition modulation. One wonders (viii) if and how topography modulation can turn a ‘simple’ 2D material into a chiral, with all its attributes [9] of physical behaviors.
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[2] J.-J. Zhang et al. Nano Lett. 21, 785 (2021)
[3] S. Gupta et al. J. Am. Chem. Soc. 143, 3503 (2021)
[4] H. Yu et al. J. Phys. Chem. Lett. 12, 4299 (2021)
[5] Y. Gogotsi & B.I. Yakobson, Science, 367, 506 (2020)
[6] V. Artyukhov et al. Nano Lett. 20, 3240 (2020)
[7] S. Gupta et al. arXiv:2410.16242 (2024)
[8] X. Li et al. arXiv:2410.17548 (2024)
[9] H. Zhu & B.I. Yakobson, Nature Mater. 23, 316 (2024)