Spallation-induced roughness promoting high spatial frequency nanostructure formation on Cr

• Published in: Applied physics. A, Materials science & processing Materials science & processing, 2018-04, Vol.124 (4), p.1-12, Article 308
• Main Authors: Abou-Saleh, A., Karim, E. T., Maurice, C., Reynaud, S., Pigeon, F., Garrelie, F., Zhigilei, L. V., Colombier, J. P.
• Format: Article
• Language: English
• Subjects: Applied physics; Atomic force microscopy; Characterization and Evaluation of Materials; Chromium; Computer simulation; Condensed Matter Physics; Crystallography; Electron microscopy; Elongation; Engineering Sciences; Irradiation; Lasers; Machines; Manufacturing; Materials; Materials Science; Metal surfaces; Microscopy; Molecular dynamics; Morphology; Nanostructure; Nanotechnology; Optical and Electronic Materials; Physics; Physics and Astronomy; Processes; Roughness; Spallation; Surfaces and Interfaces; Thin Films
• ISSN: 0947-8396; 1432-0630
• DOI: 10.1007/s00339-018-1716-0

Interaction of ultrafast laser pulses with metal surfaces in the spallation regime can result in the formation of anisotropic nanoscale surface morphology commonly referred to as laser-induced periodic surface structures (LIPSS) or ripples. The surface structures generated by a single pulse irradiation of monocrystalline Cr samples are investigated experimentally and computationally for laser fluences that produce high spatial frequency nanostructures in the multi-pulse irradiation regime. Electron microscopy reveals distinct response of samples with different crystallographic surface orientations, with (100) surfaces exhibiting the formation of more refined nanostructure by a single pulse irradiation and a more pronounced LIPSS after two laser pulses as compared to (110) surfaces. A large-scale molecular dynamics simulation of laser interaction with a (100) Cr target provides detailed information on processes responsible for spallation of a liquid layer, redistribution of molten material, and rapid resolidification of the target. The nanoscale roughness of the resolidified surface predicted in the simulation features elongated frozen nanospikes, nanorims and nanocavities with dimensions and surface density similar to those in the surface morphology observed for (100) Cr target with atomic force microscopy. The results of the simulation suggest that the types, sizes and dimensions of the nanoscale surface features are defined by the competition between the evolution of transient liquid structures generated in the spallation process and the rapid resolidification of the surface region of the target. The spallation-induced roughness is likely to play a key role in triggering the generation of high-frequency LIPSS upon irradiation by multiple laser pulses.