MORPHOSURF - Research project

Femtosecond laser irradiation experiments in a double pulse configuration, performed on a single crystal of Nickel with surface orientation <100>, revealed the appearance of a novel nanostructuring, consisting of a hexagonal array of nanoholes or nanopeaks of ~ 25nm in diameter and depth, spaced by ~60nm. The objective of the project was to determine the different regimes of self-organization and to predict their occurrence as a function of irradiation parameters through physical modeling and artificial intelligence. The consequences of the spatio-temporal shaping of the beam in cross-polarization were particularly studied. The experimental study naturally focused on other types of metallic samples for antibacterial behavior and catalysis (Titanium, Chromium). Thus, the physical properties of this new type of surface nano-structuring have been studied to define potential applications for these surfaces.


 

The self-organization of periodic patterns is a spectacular phenomenon, omnipresent in nature, and regularly reported at the microscale in laser-surface interaction, referred as "LIPSS". Our work demonstrates the potential of ultrafast laser for the fabrication of unconventional patterns (uniform periodic nanopatterns with a sub-100nm periodicity). In an elegant way, the control of fluid flows on the nanoscale by laser irradiation is demonstrated by tuning laser parameters.
We’ve reported the formation of unconventional self-organized patterns on the 100 nm scale generated by focused ultrafast light. Irradiated surface turns to a forest of nanopeaks with the highest aspect ratio reported in the literature at the nanoscale (height 100 nm: width 20 nm with a sub-100nm periodicity). Laser beam polarization is timely controlled to prevent anisotropic energy absorption and to synchronize the laser energy delivery rate with the material dynamic response. This strategy upgrades the energy coupling and the structure growth explained by a state-of-the-art Maxwell-hydrodynamic simulation. Initiated by convective instabilities at the nanoscale, we demonstrate that the crossed pulses polarization cancels the individual response of each nano-relief due to near-field optical enhancement and enables a collective response of the dissipative structure. The uniformity of the patterns results finally from the regulation between growth and local ablation process. Extreme thermomechanical conditions are supported by both simulations and high-resolution structural measurements owing to HR-TEM microscopy.
The exploited nanostructuring strategy, relying on a timely-controlled polarization feedback, paves the way for the production of homogeneous high-aspect ratio structures for nanoengineering metamaterials. Nanostructuring of high aspect ratio regular and densely packed nanostructures, open up new avenues for improving bactericidal properties and high adhesive forces, antiphase and polarization state manipulation, localized surface plasmon resonance excitation, and extreme light confinement at the nanoscale, significantly improving surface nonlinear optical response.