Plasmonic Au–Cu Alloy Nanoparticles Exhibiting Order–Disorder Phase Transitions for Sensing and Catalysis

Plasmonic sensing leverages nanoscale transducers and straightforward optical setups to detect a wide range of phenomena, such as (bio)molecules, chemical reactions, temperature variations, and ionic strength. This versatility in sensing extends from practical devices to fundamental research applications such as monitoring changes in crystalline structures. In this work, we explore plasmonic Au–Cu alloy nanoparticles, which experience order–disorder phase transitions, including long-range superlattices. The alloy nanoparticles, fabricated through the dewetting method, are optically monitored to detect the phase transitions through their plasmonic resonance shifts while changing the temperature in a vacuum. The nanoparticles with a 50% Cu alloy composition involve a long-range incommensurate phase and were found to exhibit a lower phase transition temperature than bulk, implying a nanosize effect.