Researchers at Rice University have discovered that laser light can physically shift atoms in certain two-dimensional semiconductors called Janus transition metal dichalcogenides (TMDs). This optostriction effect, observed through changes in second harmonic generation patterns, highlights the materials' asymmetry and potential for advanced optical technologies. The finding could enable faster photonic chips and sensitive sensors.
In a study published in ACS Nano on November 14, 2025, scientists at Rice University demonstrated how light can generate mechanical forces in ultrathin Janus TMD materials, causing atomic lattice shifts. These materials, named after the two-faced Roman god Janus, feature asymmetric structures with different chemical elements in their top and bottom layers, such as molybdenum sulfur selenide stacked on molybdenum disulfide.
The team, led by Shengxi Huang, associate professor of electrical and computer engineering, used laser beams of various colors to probe the material's response. They focused on second harmonic generation (SHG), where the material emits light at twice the incoming frequency. When the laser matched the material's resonances, the typical six-pointed 'flower' SHG pattern distorted, indicating atomic movement.
"We discovered that shining light on Janus molybdenum sulfur selenide and molybdenum disulfide creates tiny, directional forces inside the material, which show up as changes in its SHG pattern," said Kunyan Zhang, a Rice doctoral alumna and lead author. "Normally, the SHG signal forms a six-pointed 'flower' shape that mirrors the crystal's symmetry. But when light pushes on the atoms, this symmetry breaks—the petals of the pattern shrink unevenly."
This phenomenon, termed optostriction, arises from light's electromagnetic field applying force to atoms, amplified by the strong layer coupling in Janus TMDs. "Janus materials are ideal for this because their uneven composition creates an enhanced coupling between layers, which makes them more sensitive to light's tiny forces," Zhang explained.
The discovery opens doors to light-based technologies that could outperform electrical systems by generating less heat. Potential applications include energy-efficient photonic chips, ultrasensitive detectors for vibrations or pressure, and tunable light sources for displays and imaging.
"Such active control could help design next-generation photonic chips, ultrasensitive detectors or quantum light sources—technologies that use light to carry and process information instead of relying on electricity," Huang said.
TMDs, composed of transition metals like molybdenum and chalcogens like sulfur or selenium, are prized for their conductivity, light absorption, and flexibility in next-generation devices. The research was funded by the National Science Foundation, Air Force Office of Scientific Research, and others.