Logarithmic trends in the surface characteristics of femtosecond laser produced self-organized microstructures on silicon

Processing of metallic and semiconductor surfaces by a femtosecond pulsed laser can be used to form self-organized quasi-periodic micro- and nano-scale structures on the surface of the material. This advanced manufacturing technique, known as Femtosecond Laser Surface Processing (FLSP), is a single step process and the self-organized micro- and nano-scale structures produced by FLSP are useful in a plethora of applications, including two-phase heat transfer, catalysis, and radiative cooling. A critical aspect governing the performance of FLSP surface structures in these applications are the physical surface characteristics including the surface roughness and average structure height. To improve the capabilities of FLSP for various applications, a deeper understanding of the influence of the laser parameters on the surface micro- and nano-scale features is needed. In this paper, silicon was chosen as the material for the investigation due to its great interest for heat transfer applications in electronic and photovoltaic systems. In this work, we establish a logarithmic trend in the average surface roughness and average microstructure height as a function of the laser fluence (energy per unit area) and pulse count (number of pulses hitting a given point in the surface). A large sweep of laser parameters was performed, and the surface roughness characteristics of the produced self-organized structures were measured through Laser Scanning Confocal Microscopy (LSCM). This work enables a deeper understanding and greater control of the self-organized surface micro- and nano-scale features formed through FLSP that lead to enhanced surface properties for a wide variety of applications.