In the realm of energy and materials science, a team of researchers from Delft University of Technology, Radboud University, and the National Institute for Materials Science in Japan has made a significant stride in understanding and imaging excitons in twisted bilayer MoS₂. This work, published in the journal Nature Nanotechnology, opens up new avenues for efficient light sources, sensing technologies, and room-temperature information processing in the energy sector.
The team, led by Laurens J. M. Westenberg and including Lumen Eek, Jort D. Verbakel, Kevin Vonk, Stijn J. H. Borggreve, Kenji Watanabe, Takashi Taniguchi, Paul de Boeij, Rodrigo Arouca, Cristiane Morais Smith, and Pantelis Bampoulis, focused on the intriguing properties of twisted two-dimensional semiconductors. These materials generate a moiré landscape, a complex pattern that can confine excitons—bound electron-hole pairs—into programmable lattices. The ability to control and image these excitons at the nanoscale is crucial for developing advanced energy technologies.
Previous studies have relied on spatially averaged far-field signals to infer the behavior of excitons within a moiré unit cell. However, these methods lack the resolution to capture nanometer-scale variations. To overcome this limitation, the researchers employed room-temperature photocurrent atomic force microscopy, a technique that allowed them to directly image excitons across the moiré of a 2° twisted bilayer MoS₂ with nanometer resolution.
The researchers observed site-selective confinement, where direct and indirect excitons localize at different stacking registries of the moiré. The contrast in their images was governed by the alignment between site-selective generation and confinement minima. This detailed imaging provides a benchmark for excitonic order and offers a device-compatible route to engineering excitonic lattices in van der Waals heterostructures.
To validate their findings, the team developed a Wannier-based moiré-exciton model that reproduced the measured energies and the moiré-induced localization of the exciton wavefunction. This model not only confirms the experimental results but also provides a theoretical framework for understanding the behavior of excitons in twisted bilayer MoS₂.
The practical applications of this research are manifold. For the energy sector, the ability to engineer and control excitonic lattices can lead to more efficient light sources, such as LEDs and lasers, and advanced sensing technologies. Additionally, the insights gained from this study can pave the way for room-temperature information processing, which is crucial for developing next-generation electronic devices.
In summary, the researchers have achieved a significant breakthrough in imaging and understanding excitons in twisted bilayer MoS₂. Their work provides a robust foundation for the development of advanced energy technologies and offers a deeper understanding of the fundamental properties of two-dimensional semiconductors. This research was published in Nature Nanotechnology, a leading journal in the field of nanotechnology and materials science.
Source: Westenberg, L.J.M., Eek, L., Verbakel, J.D. et al. Real-space imaging of moiré-confined excitons in twisted bilayer MoS₂. Nat. Nanotechnol. (2023).
This article is based on research available at arXiv.