Electron-beam-induced Contactless Manipulation of Interlayer Twist in van der Waals Heterostructures

TL;DR

This work demonstrates a non-contact method to actively reconfigure the twist between layers in graphene/hBN van der Waals heterostructures by electron-beam–induced charge injection. A grounded graphene stator and a decoupled hBN rotor form a nanoscale capacitor, where localized electron-beam charging of the hBN generates lateral electrostatic torque that drives in-plane rotation until a moiré‑energy minimum is reached. The rotation is tracked in real time by in-situ SEM and corroborated by twist-dependent Raman spectroscopy, revealing moiré‑pattern–driven changes in the graphene 2D peak and enabling estimation of the moiré wavelength and twist angle. While the method successfully overcomes static interlayer friction to induce small, directionally biased twists, the actuation is currently irreversible and subject to the energy landscape of the moiré potential; nonetheless, the results establish a foundation for on-chip, non-contact twist control with potential applications in optoelectronics, photonics, and quantum materials.

Abstract

The ability to dynamically control the relative orientation of layers in two dimensional (2D) van der Waals (vdW) heterostructures represents a critical step toward the realization of reconfigurable nanoscale devices. Existing actuation methods often rely on mechanical contact, complex architectures, or extreme operating conditions, which limit their applicability and scalability. In this work, we present a proof-of-concept demonstration of contactless electrostatic actuation based on electron-beam-induced charge injection. By locally charging an insulating hexagonal boron nitride (hBN) flake on an electrically grounded graphene layer, we create an interfacial electric field that generates in-plane electrostatic torque and induces angular displacement. We validate the induced rotation through in-situ scanning electron microscopy (SEM) and twist-dependent Raman spectroscopy.

Figures (13)

• Figure 1: a) Scanning electron micrograph of a representative graphene/hBN heterostructure. The bottom graphene layer (stator) is patterned into a square geometry. A mechanically decoupled hBN flake (rotor) is placed atop the patterned graphene (stator). The red dashed lines highlight the etched geometry of the stator. b) Conceptual representation of the device operation under electron beam irradiation. A focused electron beam (e$^-$ beam) locally charges the hBN layer, inducing a potential difference with respect to the grounded graphene. The resulting electrostatic field at the interface comprises vertical and lateral components. The lateral field exerts an in-plane torque on the hBN rotor (curved white arrow), starting rotational motion toward a new equilibrium twist angle.
• Figure 2: a) Scanning electron microscopy image of Sample S1 acquired before electron-beam exposure; the hBN flake rests on patterned graphene pads and the red dashed rectangle marks the area analysed by Raman mapping. b) Scanning electron microscopy image of the same region after electron injection, showing a counter-clockwise rotation of the flake. c) Overlay of images a) and b) reveals a net twist of $\Delta\theta \approx 3.18^{\circ}$. d) Map of the full width at half maximum (FWHM) of the graphene 2D Raman band recorded before actuation. e) Corresponding FWHM map after actuation; regions A (bare graphene) and B (graphene covered by hBN) are visible in both maps. f) Enlarged view from c) highlighting the measured rotation. g) Representative Raman spectra extracted from d). h) Corresponding spectra from e). Scale bar: 10 µm (applies to all panels).
• Figure 3: a) Scanning electron microscopy image of Sample S2 acquired before electron-beam exposure; the hBN flake rests on patterned graphene pads and the red dashed rectangle marks the area analysed by Raman mapping. b) Scanning electron microscopy image of the same region after electron injection, showing a clockwise rotation of the flake. c) Overlay of images a) and b) reveals a net twist of $\Delta\theta \approx 1.95^{\circ}$. d) Map of the full width at half maximum (FWHM) of the graphene 2D Raman band recorded before actuation. e) Corresponding FWHM map after actuation; regions A (bare graphene) and B (graphene covered by hBN) are visible in both maps. f) Enlarged view from c) highlighting the measured rotation. g) Representative Raman spectra extracted from d). h) Corresponding spectra from e). Scale bar: 10 µm (applies to all panels).
• Figure 4: Step-by-step fabrication process of the twistable graphene/hBN heterostructure. i) Patterning of monolayer graphene via electron beam lithography followed by reactive ion etching (RIE), using a resist mask. ii) Final geometry of the graphene stator after RIE. iii) Exfoliation of a hexagonal boron nitride (hBN) flake onto a separate substrate. iv) Pick-up of the hBN flake using a transparent polymer stamp. v) Dry-transfer of the hBN flake onto the patterned graphene stator. vi) Definition of gold contacts via e-beam lithography and thermal evaporation.
• Figure 5: Representative Raman spectrum from the mapped area.