Bubble Dynamics and Directional Marangoni Flow Induced by Laser Heating of Silicon Nanodisk Arrays

Journal article, 2025

Gold nanostructures have been extensively used asphotothermal heat sources in a variety of studies due to theirchemical inertness, biocompatibility, and advantageous thermo-plasmonic properties. However, gold nanostructures are prone tosurface melting and thermal deformation, which, in some cases,limit their applicability. In this study, we investigate micrometer-sized amorphous silicon nanodisk arrays as a stable andbiocompatible alternative for the particular application of photo-thermally induced microbubble formation and generation of strongdirectional Marangoni flows in water. By using time-modulatedcontinuous-wave laser heating, we show that the induced flows canmove microparticles tens of micrometers across a substrate surface.The direction of particle movement can be preselected by utilizingasymmetric pairs of nanodisk arrays as heat sources or dynamically controlled by altering the laser spot position relative to asymmetric pair of arrays. We also demonstrate that average bubble size and particle displacement positively correlate and cruciallydepend on the laser modulation frequency. These results are discussed in terms of the temporal dynamics of bubble growth followingnucleation. Our findings highlight the potential of using silicon nanostructures as substrates for generating strong thermocapillaryflows on the micrometer scale, with potential applications in chemical mixing, pumping, particle sorting, and mass transport.