Microstructure and optical properties of AgCuAl medium entropy films with nanoparticles induced by pulsed-laser dewetting

AgCuAl equimolar complex concentrated alloy (CCA) thin films are deposited on glass substrates using a high-vacuum sputtering system. The films are annealed at 400 °C for 5 min to stabilize the structure and are then dewetted using a NIR pulsed-laser system at various pulse powers, repetition rates and scan speeds to form nanoparticles. It is shown that the dewetting process prompts a diffusion of the Al atoms toward the glass substrate. The resulting low concentration of Al within the AgCuAl film results in the formation of CCA nanoparticles consisting mainly of Ag and Cu with neither elemental segregation nor phase separation. The nanoparticles exhibit local surface plasmon resonance (LSPR) peaks at wavelengths in the range of 510–550 nm. The nanoparticle size and peak wavelength vary linearly with the accumulated energy density, which is controllable through the dewetting parameters. Overall, the present results suggest that AgCuAl CCA thin films have significant potential for such applications as tuning the absorption wavelength peak.