Subnanometer imaging and controlled dynamical patterning of thermocapillary driven deformation of thin liquid films

Exploring and controlling the physical factors that determine the topography of thin liquid dielectric films are of interest in manifold fields of research in physics, applied mathematics, and engineering and have been a key aspect of many technological advancements. Visualization of thin liquid dielectric film topography and local thickness measurements are essential tools for characterizing and interpreting the underlying processes. However, achieving high sensitivity with respect to subnanometric changes in thickness via standard optical methods is challenging. We propose a combined imaging and optical patterning projection platform that is capable of optically inducing dynamical flows in thin liquid dielectric films and plasmonically resolving the resulting changes in topography and thickness. In particular, we employ the thermocapillary effect in fluids as a novel heat-based method to tune plasmonic resonances and visualize dynamical processes in thin liquid dielectric films. The presented results indicate that light-induced thermocapillary flows can form and translate droplets and create indentation patterns on demand in thin liquid dielectric films of subwavelength thickness and that plasmonic microscopy can image these fluid dynamical processes with a subnanometer sensitivity along the vertical direction.
Sensitive mapping of liquid dielectric topography and thickness variation A technique that induces and maps tiny topographical changes in thin liquid dielectric films could have applications in interfacial science and industry. Shimon Rubin, Brandon Hong and Yeshaiahu Fainman of the University of California, San Diego used a heating laser to induce thermocapillary flows in thin liquid dielectric films. These films are used, among various things, for UV photolithography of semiconductors and microelectronics applications. The team mapped the changes caused by the flows using surface plasmon resonance microscopy, a non-contact imaging method that measures changes of the collective oscillations of surface electromagnetic waves and electrons in the metal substrate. The technique successfully identified subnanometer-scale topographical changes caused by the thermocapillary flow. It overcomes problems in currently used techniques, such as white light interferometry, which is not sensitive enough to detect small, local thickness variations. The technique has many potential applications, including the study of light-induced thickness changes in photosensitive materials.