Researchers created ultrathin gold films with engineered optical structures beneath them to control how the films break apart under laser light. Dr. Thejaswi U. Tumkur and Dr. Mikhail A. Noginov led the study, published in the IEEE Journal of Selected Topics in Quantum Electronics.
The team fabricated four samples with identical chemical compositions but different optical structures by varying the thickness of underlying silica and gold layers. All samples had 10 nanometer gold films on top. Two samples showed expected dewetting behavior, where the continuous film retracted into nanoscale islands. The other two exhibited unexpected features, including broad particle size distributions and complex spatial patterns.
Laser-induced dewetting offers greater precision, speed and flexibility than thermal dewetting for patterning metallic films. It has applications in plasmonic color laser printing and metasurface fabrication. However, dewetting can be undesirable in low-emissivity window coatings and nanoscale plasmonic devices, where it shortens coating lifetime and degrades performance.
The findings show that nonlocal optical effects, working alongside thermal, capillary and fluid dynamic effects, influence how the films dewet. Finite-element simulations ruled out local electric field variations as the cause. "Our results offer a unique way of controlling the particle morphologies formed upon dewetting by engineering the underlying optical cavity," Noginov said. The approach could help reduce unwanted dewetting where laser-induced damage is undesirable.