Influence of plasmonic defects and microstructure on the formation, control and regularity of laser-induced periodic surface structures

• Applicants: Dr. Jörn Bonse; Dr. Stephan Gräf
• Subject Area: Synthesis and Properties of Functional Materials
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 530345255

Ultra-short laser pulses have attracted increasing interest in recent years for the modification of surfaces in the sub-nanometer range. Various novel applications of such surfaces are currently being discussed and actively explored, as femtosecond lasers are presently undergoing a rapid development towards high pulse repetition rates and becoming increasingly available, cheaper and more flexible. A particular focus is on a specific type of nanostructures, the so-called laser-induced periodic surface structures (LIPSS, ripples). A variety of potential applications of these grating-like LIPSS have already been demonstrated in the field of surface functionalization. Examples include structural colors (e.g. for optical effects or safety features), beneficial friction and wear reduction, variation of the wetting behavior of surfaces, and antibacterial or cell growth reducing properties for medical implants. However, the industrial application of LIPSS is often still limited by their intrinsic irregularity – a circumstance that is largely misunderstood so far and is, therefore, poorly controlled. This is where the proposed project comes in, to improve the fundamental understanding and control of the regularity of LIPSS, thus expanding their technical uses and promoting their industrial application. Based on own preliminary work of both applicants, the joint project between the Friedrich-Schiller-University Jena (FSU) and the Federal Institute for Materials Research (BAM) shall pursue an optimized approach to this current topic: Starting from the physical mechanisms of action for the formation of LIPSS (plasmonic, optical, thermodynamic), a series of initial questions were formulated and hypotheses for the regularity of LIPSS were developed from them. As a central idea, these are based on the influence of plasmonic defects and material structure on the formation of LIPSS and can be addressed by specifically varying the irradiated materials and laser irradiation conditions. To test the hypotheses, two specific and complementary material systems were developed and a work program was derived (experiments & theory). Various material systems tailored to the task, such as polycrystalline metal (Cu/Ni) alloys or semiconductor-metal (Si/Ag) micro-composites with variable microstructural size, will be developed and produced and then irradiated using different laser process strategies and parameters. Subsequently, the material modification and the regularity of the resulting nanostructures will be investigated, quantified, evaluated by surface analyses and complemented by modelling. The results of the research project promise fundamental new insights into the regularity of LIPSS, on the basis of which a significant improvement of this one-step nanostructuring technology can be expected.

• DFG Programme: Research Grants