Researchers from Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR), an autonomous institute of the Department of Science and Technology, have demonstrated for the first time that how a metal interacts with light can be actively tuned by applying mechanical strain. This finding overturns a decades-old assumption in physics that optical properties of metals are unchangeable and opens new pathways for building reconfigurable, programmable optical devices that are fully compatible with standard semiconductor manufacturing.
The research focused on metals' ability to trap and concentrate light into volumes far smaller than the wavelength of light itself, a phenomenon known as plasmon resonance that underpins technologies ranging from ultrasensitive chemical sensors and cancer diagnostics to sub-wavelength photonic circuits and metasurface-based optical components. Scientists used epitaxial ultrathin titanium nitride (TiN) films, a refractory material with gold-like plasmonic response, superior thermal and chemical stability, and full CMOS compatibility. They grew two identical 10-nanometre-thick TiN films—one strain-free on magnesium oxide substrate and one subject to controlled in-plane tensile strain induced by an aluminium scandium nitride buffer layer.
Using electron energy loss spectroscopy in a scanning transmission electron microscope, the team mapped plasmon resonance energy at near-atomic spatial resolution. The strained TiN film exhibited a pronounced blue shift of 0.30–0.45 electron volts in its plasmon resonance relative to the unstrained film, with the shift tracking the local strain distribution within the material. First-principles density functional theory calculations revealed that tensile strain systematically lowers the energy required to form nitrogen vacancies in TiN, which act as electron donors and increase free-electron concentration, thereby raising the plasma frequency and explaining the observed blue shift.
According to Prof. Bivas Saha, corresponding author and Associate Professor at JNCASR, this work shows strain is a powerful control knob for plasmonic properties that transforms plasmonics from a static platform to an active and programmable one. The research involved collaboration with Dr. Magnus Garbrecht, Vijay Bhatia, and Ashalatha Indiradevi Kamalasanan Pillai from the University of Australia and was published in the journal Nano Letters (American Chemical Society, 2026).
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