Enhanced heating by microdroplet lens in nanoparticle electrospray laser deposition

In this paper, an additive manufacturing process has been used to deposit nanoparticles on a substrate. In this innovative technique called the nano-electrospray laser deposition process, droplets of various nanosuspensions are dispensed onto a silicon substrate where subwavelength structures and bouncing droplets have been observed. An analytical model is presented for determining the temperature distribution in the substrate by considering the microdroplet as a ball lens. This lens continuously changes the focus of the laser beam as the droplet travels toward the substrate. The laser is either defocused or focused on the substrate forming locally decreased or enhanced heating near the center of the laser beam depending on the distance of the droplet from the substrate. It is found that the enhancement in heating differs for the nanosuspensions since their optical properties are different. The subwavelength structures determined from the post-pulse temperature qualitatively match with the experimental results. The steady end-period temperature is also compared with the experimentally observed temperature for bouncing droplets and the temperatures are in good agreement.