Periodic Reporting for period 1 - 2DTWIST (Electrostatic actuation of 2D-materials-based heterostructures for in situ twistronics)
Reporting period: 2023-07-01 to 2025-06-30
The 2DTWIST project aims to overcome these limitations by developing a platform for dynamic, in situ control of the twist angle in 2D heterostructures. The main objectives are:
(1) the design and fabrication of electrostatic actuators based on 2D materials, capable of inducing controlled angular motion between stacked layers;
(2) the implementation and optical/electrical characterization of dynamically twistable graphene/hBN heterostructures;
(3) the demonstration of operando modulation of moiré patterns and their associated quantum phenomena.
These advances are expected to lay the foundation for new classes of reconfigurable quantum devices, sensors, and optoelectronic components, thus addressing key scientific and technological challenges identified at the European and international levels.
1. Fabrication and Assembly of 2D Heterostructures:
Robust protocols were established for the mechanical exfoliation of large-area, high-quality monolayers of graphene and hexagonal boron nitride. The process was optimized by incorporating gold-assisted exfoliation and APTES-based surface functionalization, leading to improved yield, adhesion, and transfer uniformity. These methods allowed the reproducible assembly of van der Waals heterostructures with clean interfaces and minimal defect density. The workflow is compatible with standard microfabrication techniques, demonstrating scalability and adaptability.
2. Device Microfabrication:
Lithographic techniques, including electron beam lithography (EBL) and reactive ion etching (RIE), were employed to pattern graphene stators and define the device geometry. Gold electrodes were deposited via thermal evaporation to enable precise electrical interfacing of each heterostructure.
3. Development and Demonstration of Contactless Electrostatic Actuation:
A major scientific achievement was the proof-of-concept demonstration of contactless electrostatic actuation in graphene/hBN heterostructures, realized through electron-beam-induced charge injection. By locally charging the hBN layer with a focused scanning electron beam, an in-plane electrostatic field and lateral torque were generated, resulting in controlled angular displacement of the hBN flake relative to the underlying graphene. This approach offers a non-invasive and versatile method to modulate the twist angle directly in situ, without the need for mechanical contact or external actuators.
4. Characterization:
The induced angular displacement and interlayer reconfiguration were monitored and quantified using a combination of techniques:
-In situ SEM imaging provided real-time visualization of the rotational motion, with angular displacements of typically 2–3 degrees measured between pre- and post-actuation states.
-Spatially resolved Raman spectroscopy was employed to independently verify twist modulation by mapping changes in the full width at half maximum (FWHM) and position of the graphene 2D Raman band in the overlap region, providing a spectroscopic fingerprint of moiré pattern evolution.
Compared to previous techniques, which often require mechanical contact, external manipulation, or complex micro-electromechanical architectures, this strategy simplifies device fabrication and opens up new possibilities for scalable, reconfigurable 2D material-based systems. The actuation principle is validated by combining real-time SEM imaging with Raman spectroscopy, offering complementary and non-destructive insight into interlayer dynamics and moiré pattern evolution.
The results pave the way for next-generation applications in optoelectronics, sensing, and quantum technologies, where precise control over the twist angle can be used to engineer electronic, optical, and quantum properties on demand. The methodology demonstrated here can be extended to other material systems and integrated into advanced device architectures, offering broad versatility and compatibility with established microfabrication processes.
To ensure further uptake and success, ongoing efforts focus on developing integrated actuation schemes, refining angular precision and reversibility, and exploring scalable device concepts suitable for industrial application and technology transfer. These advances will facilitate the transition from proof-of-concept experiments to robust, practical platforms for dynamically reconfigurable 2D material devices.