Periodic Reporting for period 1 - PHOTOMOIRE (Polarization sensitive photodetection by straining moiré van der Waals superlattices)
Reporting period: 2023-06-01 to 2025-09-30
Two-dimensional moiré heterostructures formed by stacking atomically thin crystals with a small twist angle have emerged as a powerful platform for engineering electronic and optical properties beyond those of the individual layers. In these systems, the long-range periodic potential generated by the moiré superlattice gives rise to novel excitonic, valley and polarization phenomena that are highly sensitive to lattice symmetry and interlayer coupling. This sensitivity offers exceptional opportunities for optoelectronic functionality, but it also exposes a critical limitation of current approaches. Once fabricated, the optical response of these systems is essentially fixed, which severely restricts their adaptability, scalability and integration into functional devices. Moreover, uncontrolled strain introduced during fabrication often acts as a parasitic effect, leading to inhomogeneity, poor reproducibility and ambiguous interpretation of experimental results. Addressing these challenges requires a paradigm shift in which strain is no longer treated as an unavoidable artifact, but as an active and controllable degree of freedom.
The PHOTOMOIRE project is motivated by the need to establish strain as a deterministic and reversible knob for controlling polarization and light–matter interactions in marginally twisted moiré heterostructures. By combining controlled nanofabrication, in-situ nanoscale characterization and device-oriented design, the project pursues three complementary objectives. First, it will develop robust fabrication routes for high-quality twisted moiré heterostructures. Second, it will implement a state-of-the-art experimental platform capable of probing optical and electronic properties at the nanoscale while applying strain in situ. Third, it will translate these advances into prototype polarization-sensitive optoelectronic devices based on moiré superlattices.
The PHOTOMOIRE project is motivated by the need to establish strain as a deterministic and reversible knob for controlling polarization and light–matter interactions in marginally twisted moiré heterostructures. By combining controlled nanofabrication, in-situ nanoscale characterization and device-oriented design, the project pursues three complementary objectives. First, it will develop robust fabrication routes for high-quality twisted moiré heterostructures. Second, it will implement a state-of-the-art experimental platform capable of probing optical and electronic properties at the nanoscale while applying strain in situ. Third, it will translate these advances into prototype polarization-sensitive optoelectronic devices based on moiré superlattices.
The work performed within the project was structured around two complementary activities addressing both device fabrication and in-situ nanoscale characterization under controlled strain:
(a) The project established robust fabrication routes for optoelectronic devices based on two-dimensional materials integrated on flexible substrates, enabling efficient, homogeneous and reproducible strain transfer to the active layers. In particular, gold-assisted exfoliation was implemented as a key technique to prepare large-area, clean and well-adhered two-dimensional crystals, significantly reducing interfacial slippage and improving mechanical coupling between the material and the substrate. This approach allowed the reliable application of controlled strain to moiré heterostructures, overcoming common limitations associated with polymer-based transfer methods and enabling device-relevant architectures.
b) A motorized straining platform was developed and fully integrated with atomic force microscopy to enable in-situ nanoscale measurements under controlled mechanical deformation. This setup allows mapping of surface topography, moiré patterns and strain-induced features such as bubbles, while providing access to local electrical and electromechanical properties through advanced AFM techniques including Kelvin probe force microscopy and piezoresponse force microscopy. In addition, the platform was combined with co-localized Raman spectroscopy under applied strain, enabling direct correlation between structural, vibrational and functional responses at the nanoscale.
(a) The project established robust fabrication routes for optoelectronic devices based on two-dimensional materials integrated on flexible substrates, enabling efficient, homogeneous and reproducible strain transfer to the active layers. In particular, gold-assisted exfoliation was implemented as a key technique to prepare large-area, clean and well-adhered two-dimensional crystals, significantly reducing interfacial slippage and improving mechanical coupling between the material and the substrate. This approach allowed the reliable application of controlled strain to moiré heterostructures, overcoming common limitations associated with polymer-based transfer methods and enabling device-relevant architectures.
b) A motorized straining platform was developed and fully integrated with atomic force microscopy to enable in-situ nanoscale measurements under controlled mechanical deformation. This setup allows mapping of surface topography, moiré patterns and strain-induced features such as bubbles, while providing access to local electrical and electromechanical properties through advanced AFM techniques including Kelvin probe force microscopy and piezoresponse force microscopy. In addition, the platform was combined with co-localized Raman spectroscopy under applied strain, enabling direct correlation between structural, vibrational and functional responses at the nanoscale.
The project has delivered a set of complementary scientific and technological results that advance the state of the art in strain-engineered optoelectronics based on two-dimensional materials. The main outcome is the demonstration of optoelectronic device architectures fabricated on flexible substrates, enabling efficient and homogeneous strain transfer to two-dimensional active layers and providing a robust platform for the controlled modulation of their optical and electrical properties. This was enabled by the implementation of gold-assisted exfoliation as a key fabrication strategy, which significantly improves interfacial adhesion and reduces slippage, thereby ensuring reliable and reproducible strain coupling.
In parallel, the project established an advanced motorized straining platform fully integrated with atomic force microscopy, enabling in-situ nanoscale characterization under controlled mechanical deformation. This setup allows simultaneous mapping of surface topography, moiré superlattices and strain-induced features, such as bubbles, while providing direct access to local electrical and electromechanical responses through Kelvin probe force microscopy and piezoresponse force microscopy. The integration of co-localized Raman spectroscopy under applied strain further enables direct correlation between structural, vibrational and functional responses at the nanoscale.
Together, these results provide a versatile experimental framework for investigating strain-driven phenomena in moiré heterostructures and lay the foundations for the development of adaptive, polarization-sensitive optoelectronic devices. The methodologies and tools developed within the project are broadly transferable to other two-dimensional material systems, supporting further uptake in both fundamental research and emerging device applications.
In parallel, the project established an advanced motorized straining platform fully integrated with atomic force microscopy, enabling in-situ nanoscale characterization under controlled mechanical deformation. This setup allows simultaneous mapping of surface topography, moiré superlattices and strain-induced features, such as bubbles, while providing direct access to local electrical and electromechanical responses through Kelvin probe force microscopy and piezoresponse force microscopy. The integration of co-localized Raman spectroscopy under applied strain further enables direct correlation between structural, vibrational and functional responses at the nanoscale.
Together, these results provide a versatile experimental framework for investigating strain-driven phenomena in moiré heterostructures and lay the foundations for the development of adaptive, polarization-sensitive optoelectronic devices. The methodologies and tools developed within the project are broadly transferable to other two-dimensional material systems, supporting further uptake in both fundamental research and emerging device applications.