Boosted Spontaneous Formation of High‐Aspect Ratio Nanopeaks on Ultrafast Laser‐Irradiated Ni Surface

Abstract

The capacity to synthesize and design highly intricated nanoscale objects of different sizes, surfaces, and shapes dramatically conditions the development of multifunctional nanomaterials. Ultrafast laser technology holds great promise as a contactless process able to rationally and rapidly manufacture complex nanostructures bringing innovative surface functions. The most critical challenge in controlling the growth of laser‐induced structures below the light diffraction limit is the absence of external order associated to the inherent local interaction due to the self‐organizing nature of the phenomenon. Here high aspect‐ratio nanopatterns driven by near‐field surface coupling and architectured by timely‐controlled polarization pulse shaping are reported. Electromagnetic coupled with hydrodynamic simulations reveal why this unique optical manipulation allows peaks generation by inhomogeneous local absorption sustained by nanoscale convection. The obtained high aspect‐ratio surface nanotopography is expected to prevent bacterial proliferation, and have great potential for catalysis, vacuum to deep UV photonics and sensing.

Beyond the Microscale: Advances in Surface Nanopatterning by Laser‐Driven Self‐Organization

“…These meticulously arranged structures are reported across diverse materials, including diamond, titanium and nickel. These structures exhibit an array of shapes, such as nanohexagons, [69] nanobumps, [76,91] nanohumps, [76] nanocrosshatch, [77] nanobreathfigure, [74] nanolabyrinthine patterns, [77] and high aspect ratio nanopeaks. [92] In general, HSFL are created by thermal convection, which arises from the interplay of light absorption fluctuations caused by surface reliefs and the fluid dynamics of the free surface between laser pulses.…”

“…These meticulously arranged structures are reported across diverse materials, including diamond, titanium and nickel. These structures exhibit an array of shapes, such as nanohexagons, [ 69 ] nanobumps, [ 76,91 ] nanohumps, [ 76 ] nanocrosshatch, [ 77 ] nanobreathfigure, [ 74 ] nanolabyrinthine patterns, [ 77 ] and high aspect ratio nanopeaks. [ 92 ]…”

“…Various types of 2D surface patterning have been reported, including patterns with hexagonal, [67][68][69] triangular, [70,71] spherical, [72] square, [73] labyrinthine, [74] or chaotic [75] symmetries, featuring both positive and negative reliefs such as humps, [76] bumps, [75] peaks, [74] and spikes. [77] Achieving a remarkably uniform establishment of these microscale patterns, independently of the oriented near-field optical effects on the local nanotopography, requires a more global and collective perspective.…”

Learning PDE to Model Self-Organization of Matter

“…This functional dependence is complex, with abrupt boundaries between pattern types for continuous variation of laser properties [ 17 ]. Pattern features of interest, such as rotational invariance, characteristic length, and feature height, for example, also show interesting dependence on laser parameters [ 2 , 17 , 18 ] and novel structures that can be reproduced reliably have recently been observed [ 18 , 19 ].…”

“…The photoexcited material evolves in a non-deterministic way due to stochastic surface roughness that may trigger local nonlinear optical response and collective thermomechanical response. In that far from equilibrium conditions, a deterministic approach is able to explain specific nanostructuring regimes [ 19 ] but fails to predict the coexistence and the transition between several nanopatterns.…”