Laser dewetting mechanism and antibacterial properties of Cu-Al based medium entropy alloy films

High entropy alloys (HEAs) have attracted significant interest in recent decades due to their unique microstructures and many favorable properties, including high mechanical strength, good thermal stability and excellent corrosion resistance. In the present study, three Cu-Al based medium entropy alloys (MEAs), namely CuAlAg (CAA), CuAlZn (CAZ) and CuAlV (CAV), are deposited on glass substrates using a high-vacuum sputtering system. The as-sputtered MEA films (MEAFs) are processed by Rapid Thermal Annealing (RTA) for 5 min in order to stabilize their microstructures and are then dewetted using a near infrared (NIR) fiber laser system with various repetition rates, pulse powers and scan speeds to produce nanoparticle structures. Finally, the antibacterial properties of the MEAFs and dewetted films are investigated using three bacterial strains, namely Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus. It is shown that the particle size of the dewetted films decreases as the accumulated energy (AE) density increases. The smaller particle size leads to a blue shift of the localized surface plasmon resonance (LSPR) absorption peak wavelength as a result of the greater uniformity of the induced electromagnetic field. In the dewetting process, the Ag and Cu elements of the MEAFs form particles, while the Al atoms are repelled to the bottom or surrounding region of the nanoparticles, and the Zn and V atoms remain on the glass surface. The MEAFs and dewetted films show an antibacterial efficiency of 100% for all three bacterial strains after 24 h. Moreover, the bacterial growth curves indicate that the majority of the bacteria are destroyed within 4–5 h of contact. The antibacterial effect of the MEAFs and dewetted films is attributed to the production of reactive oxygen species (ROS) and the release of metal ions, which collectively destroy the cell membranes and lead to cell shrinkage and death. For all of the MEAFs, the antibacterial performance improves after dewetting as a result of the increased surface contact area provided by the nanoparticles. Overall, the present results confirm the effectiveness of MEAs and dewetted films in realizing thin-film coatings with enhanced antibacterial properties.