AFM Materials Journal Club

Twistable electronics with dynamically rotatable heterostructures

by Rebeca Ribeiro-Palau, Changjian Zhang, Kenji Watanabe, Takashi Taniguchi, James Hone, and Cory R. Dean.

Science 17th Aug 2018: Vol. 361, Issue 6403, pp. 690-693

The electrical properties of 2D materials in a van der Waals heterostructure are now known to vary with the relative angle between layers. This effect was first discovered by measurements in aligned structures of graphene on hexagonal boron nitride (BN). The authors used a BN/graphene/BN heterostructure and managed to change the relative angle between the upper most layers by using the NanoMan software of the Dimension Icon AFM. The manipulation of the angular alignment allowed them to point out new optical, mechanical (also measured with the AFM), and electrical properties of the heterostructure. In their report, optical measurements, using Raman spectroscopy, ensured the alignment of the layers and allowed a direct comparison with previous results, proving the capability to align layers in a heterostructure. The authors also measured the frictional force between BN/graphene layers, which turned out to be highly dependent on the angular orientation. This increase of the friction close to the aligned position is attributed to the presence of a superimposed moiré potential. The effects of this superpotential are also observed in electron transport measurements.

In their electrical measurements, which show an angular control <0.2 degree rotation between layers, the presence of a second peak of high resistance (or satellite peak) when the Fermi energy is varied reflects the existence of the moiré potential, and it is a clear signature of an electronic band structure modification. Satellite resistance peaks were observed to diminish in intensity and to move further away in energy from the charge neutrality point as the angular misalignment increased. The possibility to control the angular orientation between 2D materials using the AFM provides the ability to dynamically tune the optical, mechanical and electronic properties of 2D heterostructures, providing new tools in device engineering, which can be extended to other 2D materials fabricated into heterostructures.