Mechanical Control of Plasmon Resonances in Ultrathin Metals

Plasmon resonances arise from the collective oscillations of free electrons in conductive media, enabling strong light-matter interactions. In contrast to semiconductors, the plasmonic response of metals is regarded as intrinsically fixed by their large carrier density and electronic structure and therefore relatively insensitive to external perturbations such as mechanical strain. Here, we show conclusive experimental evidence that plasmon resonances in metals can be actively tuned through strain engineering. Using epitaxial ultrathin titanium nitride (TiN) films, we demonstrate that in-plane tensile strain produces a pronounced blue shift of both unscreened and screened plasmon modes relative to unstrained films of identical thickness, with the magnitude of the shift closely tracking the local strain distribution. First-principles calculations reveal that strain modifies the local defect landscape, which alters the electronic structure, governing the plasmonic response. These results establish strain as an effective control knob for plasmonic properties in metals, enabling mechanically reconfigurable plasmonic and nanophotonic platforms.