van der Waals Heterostructures with High Accuracy Rotational Alignment

TLDR

The authors aim to realize van der Waals heterostructures with precise rotational alignment and demonstrate their functionality via resonant tunneling double bilayer graphene devices. They achieve this by successive monolayer graphene transfers to form Bernal‑stacked bilayers and by fabricating double bilayer graphene heterostructures separated by hexagonal boron‑nitride dielectrics. Raman, STM, and tunneling spectroscopy confirm Bernal stacking, while dual‑gated transport shows a field‑induced band gap in the bilayer graphene.

Abstract

We describe the realization of van der Waals (vdW) heterostructures with accurate rotational alignment of individual layer crystal axes. We illustrate the approach by demonstrating a Bernal-stacked bilayer graphene formed using successive transfers of monolayer graphene flakes. The Raman spectra of this artificial bilayer graphene possess a wide 2D band, which is best fit by four Lorentzians, consistent with Bernal stacking. Scanning tunneling microscopy reveals no moiré pattern on the artificial bilayer graphene, and tunneling spectroscopy as a function of gate voltage reveals a constant density of states, also in agreement with Bernal stacking. In addition, electron transport probed in dual-gated samples reveals a band gap opening as a function of transverse electric field. To illustrate the applicability of this technique to realize vdW heterostructuctures in which the functionality is critically dependent on rotational alignment, we demonstrate resonant tunneling double bilayer graphene heterostructures separated by hexagonal boron-nitride dielectric.