Researchers at Rice University have unveiled a groundbreaking discovery in the field of two-dimensional materials, specifically focusing on a subclass known as Janus transition metal dichalcogenides (TMDs). These atomically thin semiconductors exhibit a remarkable ability: light not only interacts with them but also induces a subtle mechanical shift within their atomic lattice. This phenomenon, which the team explored through detailed experimental investigation, opens up promising avenues for tuning material properties using light itself, potentially revolutionizing future optoelectronic and photonic technologies.
Janus TMDs derive their name from the two-faced Roman deity, a fitting metaphor for the unique structural asymmetry inherent to these materials. Their atomic structure consists of distinct top and bottom layers made from different elements, resulting in an internal polarity that profoundly influences their interaction with electromagnetic waves. This innate electric dipole moment renders Janus materials exceptionally responsive to external stimuli such as light, setting them apart from traditional layered TMDs and enabling novel optomechanical behaviors.
Central to the study was the use of molybdenum sulfur selenide (MoSSe) layered atop molybdenum disulfide (MoS₂), forming a heterostructure whose optical properties the researchers probed using second harmonic generation (SHG) spectroscopy. SHG is a nonlinear optical process in which incident photons at a certain frequency are converted into emitted photons at twice that frequency, effectively doubling the light’s energy and providing a sensitive probe of the material’s symmetry and electronic environment. Under normal conditions, the SHG from these crystals manifests as a symmetrical six-lobed pattern mirroring their hexagonal lattice symmetry.
However, the research team made a remarkable observation: when the frequency of the incident laser light matched the material’s intrinsic resonances, the SHG pattern became distorted, losing its typical symmetry. This distortion offered a window into the subtle influence of light-induced forces within the crystal lattice. Specifically, the electromagnetic field of the incoming photons exerted a mechanical pressure—an effect known as optostriction—that displaced atoms within the Janus layers, breaking the material’s native symmetry and reshaping its optical response.
This optomechanical coupling in Janus TMDs is amplified by the material’s asymmetric layering, which enhances the interaction between the atomic sheets and the incident light. The layered heterostructure behaves like a nanoscale system in which mechanical strain and electronic excitation are intricately linked, allowing minute forces from photons to induce measurable changes in the physical structure. Detecting these forces directly is challenging due to their minuscule magnitude, but changes in the anisotropy of the SHG signal provided a powerful, indirect method to probe these internal strains.
The discovery has significant implications for the development of future photonic devices. Light-driven forces that can deform material lattices enable the design of tunable optical components that operate on extremely small scales. Unlike electronic transistors, which rely on electrical currents and are prone to resistive heating, photonic devices harnessing optomechanical effects promise faster operation speeds and vastly improved energy efficiency. Such technology could redefine the architecture of optical switches, modulators, and detectors, paving the way for faster, cooler, and more compact computing platforms.
Janus TMDs’ unique response to light also sets the stage for novel sensor designs. Their sensitivity to mechanical deformation induced by tiny optical forces could lead to ultrasensitive detectors capable of monitoring vibrations, pressure changes, or even quantum fluctuations. These capabilities are crucial for advances in areas ranging from environmental sensing to quantum information science, where precise control of light-matter interactions at the nanoscale is essential.
The researchers emphasize the broader scientific and technological potential unlocked by exploiting the structural asymmetry of Janus materials. By tuning light frequencies to specific resonances within these materials, it is possible to engineer dynamic strain fields that modulate their electronic and optical properties on demand. This tunability represents a paradigm shift in material science, where the traditional static viewpoint of crystals gives way to actively controllable, adaptive nanosystems.
Underlying the experimental achievements is a robust theoretical understanding of the complex interplay between optical fields and lattice dynamics. The team’s findings highlight how electromagnetic radiation can act as a mechanical agent, not just an energy source, within specially engineered materials. This mechanistic insight into optostriction at the atomic level offers new perspectives for manipulating other two-dimensional materials and heterostructures beyond Janus TMDs.
This cutting-edge research received support from prominent agencies, including the National Science Foundation and the U.S. Department of Energy, among others. Such investment reflects the broad interest in harnessing two-dimensional materials to create next-generation devices that merge optics, electronics, and mechanics in novel ways. As the field evolves, the intricate balance of symmetry, structure, and light-matter interaction in Janus TMD heterostructures will likely inspire a wave of innovation in nanoscale engineering.
Looking ahead, the possibilities for integrating Janus TMDs into practical technologies are immense. Their ability to respond dynamically to optical inputs can form the basis for quantum light sources, tunable lasers, and reconfigurable photonic circuits. Combined with their atomic thickness and mechanical flexibility, these materials will be central to developing wearable and flexible optoelectronics that adapt in real-time to changing environmental conditions or user demands.
This study’s findings underscore how subtle atomic-scale asymmetries in materials can yield outsized technological benefits. By revealing the optomechanical dynamics within Janus TMDs, the Rice University team has opened a new frontier at the intersection of condensed matter physics, materials science, and photonics. The integration of mechanical forces generated by light into functional materials design promises to reshape how future devices process and control information, laying the foundation for a new era of light-based technologies.
The research article, titled “Optomechanical Tuning of Second Harmonic Generation Anisotropy in Janus MoSSe/MoS₂ Heterostructures,” was published in ACS Nano and documents the experimental methodologies and detailed analyses underlying these discoveries. The authors declare no conflicts of interest, emphasizing the fundamental nature of the work as a building block toward innovative scientific applications. This groundbreaking work not only advances understanding of Janus materials but also charts a course for vibrant future research and development at the nanoscale.
Subject of Research: Transition metal dichalcogenides, two-dimensional materials
Article Title: Optomechanical Tuning of Second Harmonic Generation Anisotropy in Janus MoSSe/MoS2 Heterostructures
News Publication Date: November 4, 2025
Web References:
- Study DOI: 10.1021/acsnano.5c10861
- Rice University news site: news.rice.edu
References:
Zhang, K., Dandu, M., Hung, N., Zhang, T., Barré, E., Saito, R., Kong, J., Raja, A., & Huang, S. (2025). Optomechanical Tuning of Second Harmonic Generation Anisotropy in Janus MoSSe/MoS₂ Heterostructures. ACS Nano. DOI: 10.1021/acsnano.5c10861
Image Credits: Kunyan Zhang / Rice University
Keywords
Transition metal dichalcogenides, Two-dimensional materials, Materials science, Thin films, Semiconductors, Optoelectronics, Electronics, Light, Light-matter interactions
