Abstract 

Second-harmonic generation (SHG) in monolayer transition-metal dichalcogenides is highly sensitive to mechanical strain, often leading to signal suppression under deformation. Here, we demonstrate reconfigurable SHG in monolayer MoS2 integrated with plasmonic nanoslits, where localized plasmonic fields counteract strain-induced suppression. The plasmonic nanoslits induce strong spatially localized field enhancement, yielding an SHG enhancement of up to 8000, estimated by normalizing the signal to the illumination area, relative to MoS2 on unpatterned Au films. Applying 1.2% compressive strain increases the SHG intensity by approximately threefold relative to the unstrained state, demonstrating effective strain-enabled modulation. Upon mechanical bending, the SHG response is reversibly modulated and remains stable after an initial preconditioning regime, retaining more than 95% of its initial intensity over repeated bending cycles. This strain-adaptive platform demonstrates robust cycling stability and provides a previously unexplored strategy for dynamically reconfigurable nonlinear metasurfaces, enabling applications in wearable sensors, tunable modulators, and compact frequency converters.

A collaborative team from UNIST and Ajou University has unveiled a flexible optical device that generates a stronger light signal when bent. This achievement defies the traditional understanding that mechanical deformation diminishes optical performance, paving the way for advanced wearable sensors and flexible photonic systems.

Led by Professors Hyeong-Ryeol Park and Seon Namgung of UNIST Department of Physics, alongside Professor Young-Hwan Ahn at Ajou University, the team engineered a device capable of converting incident light into a shorter wavelength. Unlike conventional devices that depend on bulky, thick materials, this ultra-thin structure employs molybdenum disulfide (MoS2), a two-dimensional semiconductor only a few atoms thick.

While bending MoS2 typically weakens its optical signals, the researchers redesigned the architecture to focus electromagnetic energy within nanoscale gaps—merely 20 nanometers wide—that concentrate fields during compression. When bent inward, these gaps are narrow, amplifying the emitted light. On the other hand, when relaxed, they widen, diminishing the signal. This dynamic modulation renders the device both strain-sensitive and capable of real-time optical control.

Experimental results demonstrated that compressing the device by approximately 1.2% increased its second-harmonic output—converting 800 nm light to 400 nm—by nearly threefold. Within these nanoscale gaps, the local electromagnetic field exceeds 8,000 times that of a flat MoS₂ film on gold. Notably, the device maintained over 95% of its initial performance even after 190 bending cycles, with minimal material degradation.

“This nanoscale design not only enhances the optical signal but also provides inherent protection for the material,” said lead researcher Sobhagyam Sharma from UNIST. “It offers a straightforward approach to developing flexible sensors that respond to mechanical stress through changes in light emission.”

Professor Park added, “This innovation lays the groundwork for deformation sensors that operate via optical signals and offers new insights into strain effects on two-dimensional materials.”

The findings were published in Science Advances on May 8, supported by the National Research Foundation of Korea (NRF), the Institute for Information & Communications Technology Planning & Evaluation (IITP), and UNIST.

Journal Reference

Sobhagyam Sharma, Satyabrat Behera, Byung Hee Son,  et al ., “Reconfigurable second-harmonic generation via plasmonic nanoslits counteracting strain-induced suppression in monolayer MoS2,”  Sci. Adv.,  (2026).