Plasmonic Nanoparticles in Oxide Thin Films for Sensing Applications

Oxide semiconductors such as Ga2O3, ZnO, and CuO are promising materials for various applications due to their stability and tunable electronic properties. Incorporating plasmonic nanoparticles into these materials enhances their optical and electrical performance through localized surface plasmon resonance (LSPR). In this work, Ag and Au nanoparticles were embedded into Ga2O3, ZnO, and CuO thin films to study their plasmonic behaviour and evaluate their potential in temperature sensing and photodetection.

The formation of metallic nanoparticles in Ga2O3 thin films by ion implantation was demonstrated for the first time, as confirmed by optical and structural characterization. Plasmonic absorption bands appeared at 400–600 nm for Ag and 500–700 nm for Au, exhibiting red-shifts with increasing annealing temperature. Heavy ion irradiation revealed nanoparticle redistribution toward the surface and shape elongation.

A comparative study of ZnO and CuO thin films with Au nanoparticles formed by ion implantation and in situ growth was performed to investigate the temperature dependence of the LSPR. Optical transmittance measurements showed a reversible red-shift of the LSPR peak with increasing temperature, consistent with theoretical predictions.

Finally, photodetection tests revealed that, under visible light, implanted Ga2O3 films displayed noticeable sub-bandgap photocurrents attributed to defect states rather than plasmonic effects. Au-ZnO demonstrated significantly enhanced photoresponses comparatively to its undoped film, particularly under illumination resonant with the nanoparticles, suggesting that plasmonic effects were involved. In contrast, the inclusion of the nanoparticles in Au-CuO decreased its dark current, as well as its responsivity.