Self-Organization Regimes Induced by Ultrafast Laser on Surfaces in the Tens of Nanometer Scales

Abstract

A laser-irradiated surface is the paradigm of a self-organizing system, as coherent, aligned, chaotic, and complex patterns emerge at the microscale and even the nanoscale. A spectacular manifestation of dissipative structures consists of different types of randomly and periodically distributed nanostructures that arise from a homogeneous metal surface. The noninstantaneous response of the material reorganizes local surface topography down to tens of nanometers scale modifying long-range surface morphology on the impact scale. Under ultrafast laser irradiation with a regulated energy dose, the formation of nanopeaks, nanobumps, nanohumps and nanocavities patterns with 20–80 nm transverse size unit and up to 100 nm height are reported. We show that the use of crossed-polarized double laser pulse adds an extra dimension to the nanostructuring process as laser energy dose and multi-pulse feedback tune the energy gradient distribution, crossing critical values for surface self-organization regimes. The tiny dimensions of complex patterns are defined by the competition between the evolution of transient liquid structures generated in a cavitation process and the rapid resolidification of the surface region. Strongly influencing the light coupling, we reveal that initial surface roughness and type of roughness both play a crucial role in controlling the transient emergence of nanostructures during laser irradiation.

Editorial: Special Issue “Laser-Generated Periodic Nanostructures”

“…We aimed to attract both academic and industrial researchers in order to collate the current knowledge of nanomaterials and to present new ideas for future applications and new technologies. By 8 August 2021, 22 scientific articles have been published in the Special Issue [ 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 ], see .…”

“…Three “Feature Papers” [ 15 , 16 , 17 ] were invited by the Guest Editors for the adequate framing of this Special Issue. An additional 19 papers were published as regular contributions [ 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 ]. The publications in this Special Issue can generally be divided into three groups: (1) manuscripts related to self-organized laser-induced periodic surface structures [ 15 , 18 , 19 , 21 , 23 , 24 , 25 , 26 , 28 , 30 , 31 , 32 , 33 , 34 , 35 , 36 ], (2) manuscripts related to interference-based periodic surface structuring [ 17 , 22 , 27 , 29 ], or (3) manuscripts combining both approaches [ 16 , 20 ].…”

“…Several publications focus on the relevance of chemical surface alterations during or after laser-processing, including studies of superficial oxidation on the formation of specific types of LIPSS [ 18 , 23 , 24 , 25 , 30 ], chemo-capillary effects in DLIP [ 29 ], or even post-laser irradiation effects due to reactions with the environment [ 30 ]. Other publications study the fundamental mechanisms of structure formation on the basis of experimental and theoretical plasmonic approaches [ 15 , 21 , 26 ], and also in combination with a two-temperature model [ 28 ], advanced molecular dynamics simulations [ 22 ], or multi-physical hydrodynamic continuum considerations [ 31 , 34 ]. Two articles investigate in vitro the growth of different types of biological cells (either scar-forming fibroblasts or bone-forming osteoblasts) on laser-generated micro- and nanostructures for medical applications [ 19 , 25 ].…”

“…Nakhoul et al [ 31 ] employed sequences of multiple cross-polarized double-fs-laser pulses (800 nm, 25 fs, 1 kHz) to generate a plethora of nanostructures at the surface of polished single-crystalline <100> nickel surfaces, including random patterns with concentrated nanoreliefs, 1D nanostripes, or 2D hexagonal arrays, forming disordered, labyrinthine, and bumpy nanopatterns. The surface morphologies were characterized by SEM and AFM.…”

“…Four items of this Special Issue “Laser-Generated Periodic Nanostructures” [ 18 , 31 , 33 , 35 ] were selected as “Editor’s Choice” articles by the Editorial Office and the international board of Editors of Nanomaterials—based on readers’ interests, academic editors’ comments, and reviewers’ suggestions. It is supposed that such articles will be particularly interesting or important, while simultaneously aiming to provide a snapshot of some of the work published in the various research areas of the journal.…”