**Executive Summary**
Researchers from the Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR) and the University of Sydney have demonstrated that the optical properties of metals can be actively tuned through mechanical strain. This discovery, published in *Nano Letters* in 2026, overturns long-standing assumptions about fixed metallic plasma frequencies. The findings provide a new pathway for developing programmable nanophotonic devices compatible with standard semiconductor manufacturing.
**Key Points / Main Content**
* **Breakthrough in Optical Tuning**
* For the first time, researchers proved that a metal’s interaction with light (plasmon resonance) can be modified by applying mechanical strain.
* The study challenges the traditional physics assumption that the plasma frequency of a metal is fixed once its composition is determined.
* **Experimental Methodology**
* Scientists used 10-nanometre-thick epitaxial ultrathin titanium nitride (TiN) films for the study.
* The experiment compared a strain-free TiN film on a magnesium oxide (MgO) substrate against a strained film induced by an aluminium scandium nitride (Al₀.₃Sc₀.₇N) buffer layer.
* Advanced imaging and spectroscopy (EELS and DFT calculations) were used to map plasmon resonance at near-atomic resolution.
* **Scientific Findings and Mechanism**
* Strained TiN films exhibited a blue shift of 0.30–0.45 electron volts in plasmon resonance compared to unstrained films.
* Tensile strain was found to lower the energy required to form nitrogen vacancies, which act as electron donors.
* The resulting increase in free-electron concentration raises the plasma frequency, directly modifying the metal's intrinsic electronic response.
* **Material Advantages**
* Titanium nitride (TiN) was selected for its gold-like plasmonic response and superior thermal and chemical stability.
* TiN is fully compatible with complementary metal-oxide-semiconductor (CMOS) chip fabrication, making it ideal for industrial integration.
**Impact Analysis**
**Scientific Researchers**
**Impact**
The discovery provides a "control knob" for plasmonic properties, transforming plasmonics from a static platform into an active, programmable one.
**Action Required**
Utilize these findings to explore new research avenues in sub-wavelength photonic circuits and metasurface-based optical components.
**Semiconductor Manufacturers**
**Impact**
The use of CMOS-compatible materials like TiN ensures that these reconfigurable optical devices can be integrated into standard manufacturing processes.
**Action Required**
Evaluate the integration of strain-engineered TiN films into the production of programmable on-chip photonics.
**Medical and Sensor Technologists**
**Impact**
The ability to tune plasmon resonance improves the potential for ultrasensitive chemical sensors and cancer diagnostics.
**Action Required**
Incorporate tunable plasmonic materials to enhance the precision and functionality of diagnostic and sensing hardware.
Key Entities Referenced
Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR): An autonomous research institute under the Department of Science and Technology that led the breakthrough study on tuning the optical properties of metals through mechanical strain.
Prof. Bivas Saha: The lead researcher and Associate Professor at JNCASR who directed the team that discovered how to reconfigure the optical response of CMOS-compatible materials.
Department of Science and Technology (DST): The government department that oversees JNCASR and provided the administrative framework for this scientific development.
Nano Letters: The prestigious scientific journal by the American Chemical Society where the research findings on mechanical control of plasmon resonance were published.
Ministry of Science & Technology
Researchers show optical properties of metals
can be tuned opening new route to
programmable nanophotonic devices
प्रव तथ: 07 JUL 2026 4:01PM by PIB Delhi
In a significant development, researchers from Bengaluru have shown for the first time that how a metal
interacts with light can be actively tuned by applying mechanical strain. The 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.
Metals can trap and concentrate light into volumes far smaller than the wavelength of light itself, a
phenomenon known as plasmon resonance. This remarkable ability underpins a wide range of
technologies, from ultrasensitive chemical sensors and cancer diagnostics to sub-wavelength photonic
circuits and metasurface-based optical components. At the heart of this behaviour lies the plasma
frequency of the metal, which is set by its free-electron concentration and has conventionally been
considered fixed once the material composition is chosen. While researchers have used nanostructuring
and dielectric engineering to indirectly adjust plasmonic properties, directly modifying the plasma
frequency through mechanical deformation had remained largely unexplored.
Scientists at Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR), an autonomous
institute of the Department of Science and Technology (DST), used epitaxial ultrathin titanium nitride
(TiN) films to isolate the role of strain on plasmonic behaviour. TiN is a refractory material with a gold-
like plasmonic response, superior thermal and chemical stability, and full compatibility with
complementary metal-oxide-semiconductor (CMOS) chip fabrication. Two otherwise identical 10-
nanometre-thick TiN films were grown, one strain-free on a magnesium oxide (MgO) substrate, and one
subject to a controlled in-plane tensile strain induced by an aluminium scandium nitride (Al Sc N)
0.3 0.7
buffer layer with a larger crystal lattice constant.
Fig: Schematic illustration of mechanical control of plasmon resonance in ultrathin films.Using electron energy loss spectroscopy (EELS) in a scanning transmission electron microscope, Diksha
Dadhich and co-workers in Prof. Bivas Saha's group mapped the plasmon resonance energy at near-atomic
spatial resolution across both films. 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, a large and spatially resolved shift
that tracked the local strain distribution within the material. Both screened and unscreened plasmon modes
shifted consistently, providing strong evidence that strain was directly modifying the intrinsic electronic
response of the metal.
To understand the origin of this effect, the team performed first-principles density functional theory (DFT)
calculations which revealed that tensile strain systematically lowers the energy required to form nitrogen
vacancies in TiN. These vacancies act as electron donors, increasing the free-electron concentration and
thereby raising the plasma frequency, explaining the experimentally observed blue shift. Spectroscopic
ellipsometry and high-resolution X-ray diffraction measurements provided additional corroboration of this
mechanism.
“Our work shows that strain is a powerful and previously underexplored control knob for plasmonic
properties in metals. The ability to mechanically reconfigure the optical response of a CMOS-compatible
material like TiN transforms plasmonics from a static platform to an active and programmable one, with
exciting implications for on-chip photonics and optical sensing,” said Prof. Bivas Saha, corresponding
author and Associate Professor at JNCASR.
Apart from JNCASR, Dr. Magnus Garbrecht, Vijay Bhatia, and Ashalatha Indiradevi Kamalasanan Pillai
from the University of Sydney, Australia, participated in this research.
This research was published in the prestigious journal Nano Letters (American Chemical Society, 2026).
Publication link: https://doi.org/10.1021/acs.nanolett.6c01304
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