Bengaluru Scientists Discover New Way to Control Light Using Metal Strain

Metals possess the unique ability to trap and concentrate light into spaces much smaller than its wavelength through a phenomenon known as plasmon resonance.

Researchers from Bengaluru have made a breakthrough that could reshape the future of photonics by demonstrating, for the first time, that the way a metal interacts with light can be actively controlled through mechanical strain. The discovery challenges a long-standing belief in physics that the optical properties of metals remain fixed after the material is created, opening the door to programmable optical devices that are compatible with modern semiconductor manufacturing.

The study was carried out by scientists at the Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR), an autonomous institute under the Department of Science and Technology (DST), in collaboration with researchers from the University of Sydney, Australia.

Mechanical strain changes how metals respond to light

Metals possess the unique ability to trap and concentrate light into spaces much smaller than its wavelength through a phenomenon known as plasmon resonance. This property plays a vital role in technologies ranging from highly sensitive chemical sensors and cancer detection tools to advanced photonic circuits and next-generation optical components.

Until now, scientists believed that a metal's plasma frequency, which determines how it interacts with light, was fixed by its chemical composition and could not be altered without changing the material itself.

To test this assumption, the JNCASR team created two ultra-thin 10-nanometre titanium nitride (TiN) films. One film remained strain-free, while the other was subjected to carefully controlled tensile strain using a specially designed buffer layer. Titanium nitride was selected because it offers plasmonic properties similar to gold while providing greater thermal stability and compatibility with standard CMOS semiconductor fabrication.

Advanced imaging reveals a measurable optical shift

Using electron energy loss spectroscopy (EELS) inside a scanning transmission electron microscope, the researchers examined how both films interacted with light at nearly atomic resolution. The strained titanium nitride film displayed a significant blue shift of 0.30 to 0.45 electron volts in its plasmon resonance compared with the unstrained sample. The shift closely matched variations in the strain across the material, providing clear evidence that mechanical deformation directly altered the metal's intrinsic electronic behaviour.

To understand why this happened, the team performed density functional theory (DFT) calculations. The analysis showed that tensile strain makes it easier for nitrogen vacancies to form inside the titanium nitride crystal. These vacancies release additional electrons, increasing the metal's free-electron concentration and raising its plasma frequency, which explains the observed optical shift. Additional measurements using spectroscopic ellipsometry and high-resolution X-ray diffraction confirmed the findings.

Discovery could enable programmable photonic technologies

According to Prof. Bivas Saha, Associate Professor at JNCASR and the study's corresponding author, the research introduces mechanical strain as a powerful new method for controlling plasmonic behaviour in metals. He said the discovery transforms plasmonics from a static technology into an active and programmable platform. Since titanium nitride is already compatible with semiconductor manufacturing processes, the findings could accelerate the development of reconfigurable optical chips, advanced sensors and integrated photonic devices for future computing and communication technologies.

The research also involved Diksha Dadhich and colleagues from Prof. Saha's group at JNCASR, along with Dr. Magnus Garbrecht, Vijay Bhatia and Ashalatha Indiradevi Kamalasanan Pillai from the University of Sydney. The findings have been published in the 2026 edition of Nano Letters, a leading journal of the American Chemical Society.