Laser-induced Periodic Surface Structures Research Articles

Impact of Hybrid Electromagnetic Surface Modes on the Formation of Low Spatial Frequency LIPSS: A Universal Approach

AbstractIn this article, the impact of the excited electromagnetic surface modes in a comprehensive investigation of the formation of laser‐induced periodic surface structures (LIPSS) is analyzed. It is demonstrated that the electromagnetic origin of low spatial‐frequency LIPSS (LSFL) is the frequency detuning between propagating and localized modes due to their coupling/hybridization. The influence of the pattern profile, inhomogeneity, and material type on the coupling strength, electric‐field spatial distribution, and associated near‐field scattering are highlighted. Exploiting the potential of the approach, evidence of a universal manifestation of LSFLs is provided irrespective of the material and the authors are able to predict and validate the experimentally‐proven lower limit of LSFL periodicity (i.e., λL/2, where λL stands for the laser wavelength). Furthermore, the analysis of the electromagnetic modes predicts that the periodicity of LSFL is practically unaffected by the laser fluence, while a suppression of LSFL at high excitation levels or large number of pulses is also predicted. It is also shown that plasmonic‐active materials are not necessary for LSFL formation perpendicular to polarization. Toward these directions, an important generic metric, namely the resonance quality factor, is additionally inserted. The approach can, thus, serve as a guide for controlling laser‐induced surface topography.

Bulk ceramics of lanthanum hexaboride with enhanced spectral selectivity and photothermal efficiency for novel hybrid thermal-thermionic solar absorbers

Lanthanum hexaboride (LaB6) single-crystals are known from a long time for their excellent thermionic and field-assisted electron-emitting properties. Recently, multi-crystalline ceramics, which offer several technological advantages over single-crystals, have been studied as well, proving a low work function and Richardson constant, in addition to favorable optical properties for high-temperature solar radiation absorbers. However, to fully disclose to LaB6 ceramics the novel application of a double-function bulk thermionic emitter, enabled by the direct absorption of solar radiation, and, at the same time, thermodynamic solar absorber for Concentrating Solar Power (CSP), their optical properties should be further optimized. The ideal result, consisting in the selective increase of the solar absorptance and decrease of the thermal emittance, thus increasing both the spectral selectivity and the photothermal efficiency of the absorber, has been obtained in this work by realizing Laser-Induced Periodic Surface Structures (LIPSS) on the ceramic surface by means of femtosecond-laser treatments. LIPPS formation has been investigated as a function of the accumulated laser fluence.

Revealing damage evolution and ablation behavior of SiC/SiC ceramic matrix composites by picosecond laser high-efficiency ablation

The picosecond laser was utilized to fabricate the slanting microholes efficiently on SiC/SiC ceramic matrix composites. The machining damage, material oxidation, and temperature field were mainly analyzed through static and in-situ detections. The damage evolution and ablation behavior of SiC/SiC composites were qualitatively and quantitatively revealed. The results showed that the lowest peak temperature of the slanting microhole was 282.6 °C. The heat accumulation effect and thermal stress that was tensile stress in nature present caused recasts, microcracks, fiber fracture, fiber debonding, and fiber stripping. Fibers and matrix underwent slight oxidation, forming SiO2 recasts through the phase transition. The pulse energy, frequency, and inclination angle regularly affected the quantity, size, and distribution of microcracks, material removal rate (MRR), and hole wall roughness. The maximum MRR was about 2.5 mm3/s, corresponding to the minimum time was 0.9 s. The circularly polarized picosecond laser could process parallel striped laser-induced periodic surface structures (LIPSS) on the hole wall.

Fabrication of Hybrid Micro/Nano Structures on Titanium by Vector Femtosecond Laser Beam

The morphology of laser-induced periodic surface structures (LIPSS) and micro/nanostructures may be influenced by laser optics or process parameters. This study focused on two beam profiles, Gaussian and vector beams. Vector beam is an annular beam with a null intensity at its center. Radial and azimuthal polarization are the common states of polarization. We investigated Gaussian and vector femtosecond laser beams with the wavelength of 515 nm irradiated on titanium to analyze the ablation crater characterization and the ablation threshold of titanium. Finally, we conducted an experiment on the fabrication of the hybrid micro/nanostructures via spot-by-spot vector beam.

Polarization‐Modulated Patterned Laser Sculpturing of Optical Functional Hierarchical Micro/Nanostructures

AbstractHierarchical micro/nanostructures have garnered considerable attention for their capabilities in light modulation, but the flexible fabrication of designed optical functional structures at both micro and nano scales remains challenging. Here, a polarization‐modulated patterned laser ablation method complemented by flowing liquid is proposed to fabricate hierarchical microgrooves featuring tunable cross‐sections and engraved surface nanostructures with controllable periods and orientations. The liquid‐assisted ablation counters the shielding effect of ablation debris through laser‐induced microjets, ensuring accurate control of the microgroove's shape by modulating the laser pattern in the focal plane. Simultaneously, the absence of debris also permits the consistent formation of laser‐induced periodic surface structures (LIPSS) across the microgrooves. The LIPSS's period and orientation can be finely adjusted by manipulating the pulse energy and polarization within the patterned laser spot, facilitating the adaptable creation of hierarchical micro/nanostructures for optical application needs. As a demonstration, blazed gratings featuring orientation‐customized LIPSS are fabricated, which exhibit polarization‐dependent diffraction efficiency. The laser fabrication technique offers a highly versatile solution for sculpturing shape‐controllable hierarchical gratings on hard‐to‐machine materials, paving the way for the swift production of customized optical elements.

Preparation of laser induced periodic surface structures for gas sensing thin films and gas sensing verification of a NiO based sensor structure

Abstract This study presents different approaches to increase the sensing area of NiO based semiconducting metal oxide gas sensors. Micro- and nanopatterned laser induced periodic surface structures (LIPSS) are generated on silicon and Si/SiO2 substrates. The surface morphologies of the fabricated samples are examined by FE SEM. We select the silicon samples with an intermediate Si3N4 layer due to its superior isolation quality over the thermal oxide for evaluating the hydrogen and acetone sensitivity of a NiO based test sensor.

Polarization-Dependent Anisotropy of LIPSSs' Morphology Evolution on a Single-Crystal Silicon Surface.

Utilizing the principle of laser-induced periodic surface structures (LIPSSs), this research delves into the morphological evolution of single-crystal silicon surfaces irradiated by a near-infrared picosecond laser through a scanning mode. With the increase in laser energy density, the nanostructure morphology on single-crystal silicon surfaces induced by incident lasers with different polarization directions sequentially produces high spatial-frequency LIPSSs (HSFLs) with a period of 220 nm ± 10 nm parallel to the laser polarization, low spatial-frequency LIPSSs (LSFLs) with a period of 770 nm ± 85 nm perpendicular to the direction of the polarization, and groove structures. Furthermore, by varying the angle between the laser polarization and the scanning direction, the study examined the combined anisotropic effects of the laser polarization scanning direction angle and the laser polarization crystal orientation angle on the genesis of LIPSSs on single-crystal silicon (100) surfaces. The experiments revealed polarization-related anisotropic characteristics in the morphology of HSFLs. It was found that when the polarization angle approached 45°, the regularity of the LSFLs deteriorated, the modification width decreased, and the periodicity increased. This is critical for the precise control of the LSFLs' morphology.

Revealing a spontaneous two-stage process in femtosecond laser-induced fully-oxidized nanostructures

Femtosecond laser interactions with matter facilitate the creation of diverse structures on material surfaces, including laser induced periodic surface structures (LIPSS), ablation nanoparticles, sub-diffraction nanogrooves, and plasmonic nanostructures. In this study, we reveal a unique nanostructure on silicon induced by femtosecond laser irradiation, distinguished by its pea-shaped morphology. At the center of this nanostructure, a nano-slit is oriented perpendicular to the laser polarization. The nano-slit penetrates the pea-shaped nanostructure and an underlying layer with a depth of approximately 600 nm. Energy dispersive X-ray spectroscopy (EDS) analysis confirms that the nanostructure and the underlying layer consist entirely of silicon oxide. A spontaneous two-stage oxidation process is proposed to explain the formation mechanism of fully-oxidized nanostructures. The presence of nano-slits endows the oxide nanostructures with polarization sensitivity, which shows the potential in applications such as optical encryption and data storage. In addition, the spontaneous two-stage oxidation process allows for the maskless fabrication of oxide nanowires with a precision down to hundreds of nanometers, providing the flexibility to produce arbitrary nanostructures. This capability opens up new possibilities for manipulating light beams and enabling on-chip nano-glass printing.

Direct Fabrication of Te-Doped Black Si with an Enhanced Photoelectric Performance by Femtosecond Laser Irradiation under Water.

Tellurium (Te)-doped black silicon (Si) with enhanced absorption and photoelectric performance over a broad wavelength range of 0.2-2.5 μm was obtained using femtosecond (fs) laser irradiation in liquid water. Prior to laser irradiation, the Si sample was covered with a Te thin film (thickness 200 nm) over an adhesion layer of Cr (thickness 5 nm). Surface analyses by scanning electron microscopy and three-dimensional confocal microscopy evidence the presence of hierarchical surface structures combining quasi-periodic stripes with a spatial period of about 5 μm and subwavelength laser-induced periodic surface structures directed in directions parallel and perpendicular to the direction of the laser polarization, respectively. Moreover, the incorporation of Te generates intermediate levels within the Si bandgap. The Te-doped black Si shows a significant enhancement of the absorption, which reaches values of about 48% in the UV and visible (0.2-1.1 μm) and 70% in the near-infrared (1.1-2.5 μm) spectral ranges, respectively, due to the synergistic effects of multiscale surface structures and Te incorporation. Moreover, the surface reflectance is reduced to almost zero across the entire spectrum. The Te-doped black Si sample is used to realize a photodetector which displays an impressive photoelectric capability, being characterized by a responsivity of 328 mA/W, and an external quantum efficiency of 49.27% at a voltage bias of -10 V for 1064 nm light illumination, with rising and falling times of 55 and 67 ms, respectively. These figures remarkably outperform the response of unprocessed Si under the same experimental conditions.

Colouration of diamond surfaces by laser-induced periodic surface structuring

Colouration of diamond surfaces by laser-induced periodic surface structuring

Biofilm growth on laser-induced periodic surface structures (LIPSS) of AISI 316L stainless steel

Biofilm growth on laser-induced periodic surface structures (LIPSS) of AISI 316L stainless steel

Laser nanostructured metasurfaces in Nb superconducting thin films

Superconducting Nb thin films have been nanostructured by means of a femtosecond UV laser. Laser induced periodic surface structures (LIPSS) with lateral modulation of ≈250nm and depth smaller than amplitude (≲20nm from crest to trough) are obtained for optimized laser scanning conditions over the film surface, i.e. power, frequency, scanning speed and polarization. This provides a fast and scalable procedure of surface control at the nanoscale. In thin films, control over the kinetics of the LIPSS formation process has been crucial. Untreated and laser-patterned samples have been characterized by electron and atomic force microscopy as well as by local and global magnetometry. The superconducting properties reveal anisotropic behavior in accordance with the observed topography. The imprinted LIPSS define channels for anisotropic current flow and flux penetration. At low temperatures, magnetic flux avalanches are promoted by the increased critical current density, though flux tends to be channeled along the LIPSS. In general, directional flux penetration is observed, being a useful feature in fluxonic devices. Scalability allows us to pattern areas of the order of cm2/min.

Microstructure Formations Resulting from Nanosecond and Picosecond Laser Irradiation of a Ti-Based Alloy under Controlled Atmospheric Conditions and Optimization of the Irradiation Process.

This paper presents a study and comparison of surface effects induced by picosecond and nanosecond laser modification of a Ti6Al4V alloy surface under different ambient conditions: air and argon- and nitrogen-rich atmospheres. Detailed surface characterization was performed for all experimental conditions. Damage threshold fluences for picosecond and nanosecond laser irradiation in all three ambient conditions were determined. The observed surface features were a resolidified pool of molten material, craters, hydrodynamic effects and parallel periodic surface structures. Laser-induced periodic surface structures are formed by multi-mode-beam nanosecond laser action and picosecond laser action. Crown-like structures at crater rims are specific features for picosecond Nd:YAG laser action in argon-rich ambient conditions. Elemental analysis of the surfaces indicated nitride compound formation only in the nitrogen-rich ambient conditions. The constituents of the formed plasma were also investigated. Exploring the impact of process control parameters on output responses has been undertaken within the context of laser modification under different environmental conditions. Parametric optimization of the nanosecond laser modification was carried out by implementing an advanced method based on Taguchi's parametric design and multivariate statistical techniques, and optimal settings are proposed for each atmosphere.

Enhancement of Metal Nanostructure Deposition on Silicon Laser-Induced Periodic Surface Structures by Galvanic Replacement.

We report a chemically motivated, single-step method to enhance metal deposition onto silicon laser-induced periodic surface structures (LIPSSs) using reactive laser ablation in liquid (RLAL). Galvanic replacement (GR) reactions were used in conjunction with RLAL (GR-RLAL) to promote the deposition of Au and Cu nanostructures onto a Si LIPSS. To increase the deposition of Au, sacrificial metals Cu, Fe, and Zn were used; Fe and Zn also enhanced the deposition of Cu. We show that the deposited metal content, surface morphology, and metal crystallite size can be tuned based on the difference in electrochemical potentials of the deposited and sacrificial metal. Compared to the Au and Cu reference samples, GR more than doubled the metal content on the LIPSS and reduced metal crystallite sizes by up to 20%. The ability to tune the metal content and crystalline domain size simultaneously makes GR-RLAL a potentially useful approach in the manufacturing of functional metal-LIPSS materials such as surface-enhanced Raman spectroscopy substrates.

Wavelength selection for femtosecond laser processing of materials: Comparison of ablation efficiency and surface quality

We investigated the effects of the femtosecond laser wavelengths λ = 1035, 515, and 345 nm on the laser ablation of 64FeNi alloy (Invar). The ablation rate and ablation efficiency for the three wavelengths were obtained through material-removal experiments of stationary irradiation and laser scanning, respectively. Among laser–matter interaction parameters, the effective penetration depth (α−1) and ablation threshold fluence (Fth) could be estimated from the experiments and were found to be proportional to λ. The ablation rate and ablation efficiency for the peak fluence range of 0.2 J/cm2 < F0 < 1.0 J/cm2 and F0 > 1.0 J/cm2 were the highest at λ = 515 and 1035 nm, respectively, which could be confirmed by using analytical models with α−1 and Fth. The smoothest (roughest) processed surfaces could be obtained at λ = 345 nm (1035 nm) owing to the shortest (longest) periodicity of laser-induced periodic surface structures. Thus, surface smoothing at λ = 345 nm over a certain ablation depth after ablation at λ = 1035 nm, i.e., double-wavelength ablation, can be used for improving surface quality. These results can help in the selection of the proper λ for implementing precise laser micromachining with high productivity.

Femtosecond laser induced periodic surface structures on crystals: Formation, evolution and application

In the research field of laser induced periodic surface structures (LIPSSs), the ones located at the superficial surface of the solid materials (s-LIPSSs) induced by femtosecond laser have been widely investigated. It is noticed that, the formation of s-LIPSSs is limited to a relatively narrow parameter window and, as the parameters are tailored, such structures would evolve into novel topographies which possess laser-ablated micro-grooves with LIPSSs being deeply located at the groove-bottoms (d-LIPSSs). In this work, both s-LIPSSs and d-LIPSSs are produced on the surface of Nd:LGGG crystal by using femtosecond laser irradiation. Experimental investigations and numerical modeling convince the crucial role of surface plasmon polariton excitation in the formation of both structures. The evolution of surface topographies and the dependence of LIPSSs-periods on the fabricating parameters can be mainly ascribed to the feedback mechanisms of s-LIPSSs and laser-induced micro-grooves. Furthermore, based on the d-LIPSSs, a novel approach is proposed to fabricate 2-dimensional surface with orthogonal dual-periods. Such structure shows enhanced polarization-sensitive antireflectivity within long wavelength range and the ability for NIR detection, which is superior to the traditional surface structure composed of s-LIPSSs.

Oxidation-driven 2D LIPSS on amorphous Si films atop metal layers: The interplay of near-field and far-field effects

We investigate the formation of Laser-Induced Periodic Surface Structures (LIPSS) on amorphous Si films coated on Al using circularly polarized femtosecond lasers. By controlling laser fluence, we induce oxidation-based surface patterns, with their regularity governed by the interplay between near-field and far-field contributions. Achieving the right balance between these effects results in a consistent hexagonal pattern. Varying the underlying metal type further revealed its impact on pattern quality: strong far-field contributions led to irregular patterns, while dominant near-field effects resulted in extensive oxidation. Our study reveals the critical balance between near-field and far-field effects in optimizing 2D LIPSS patterns, emphasizing the role of the underlying metal.

Laser‐Induced Periodic Surface Structures in Polymers with Tailored Laser Fields

In this work, laser‐induced periodic surface structures (LIPSS) are generated on the surface of thin films of poly(trimethylene terephthalate) (PTT) fabricated by spin coating on silicon. Previous studies have shown the appearance of LIPSS in this type of materials with femtosecond laser pulses in the near‐infrared region of the spectrum, despite the extremely low absorption of the polymer. The present work consists of an exploration of the effect of adding complexity to the femtosecond laser fields employed for irradiation. Changes in the repetition rate of the pulse train, the pulse duration, and the pulse temporal chirp are explored, and conditions for optimum LIPSS formation are identified. The effects of these modifications on the polymer surface topography, assessed by atomic force microscopy, are described and discussed.

Unraveling the formation dynamics of metallic femtosecond laser induced periodic surface structures

Femtosecond laser surface processing (FLSP) is an emerging fabrication technique to efficiently control the surface morphology of many types of materials including metals. However, the theoretical understanding of the FLSP formation dynamics is not a trivial task, since it involves the interaction of various physical processes (electromagnetic, thermal, fluid dynamics) and remains relatively unexplored. In this work, we tackle this problem and present rigorous theoretical results relevant to low-fluence FLSP that accurately match the outcomes of an experimental campaign focused on the formation dynamics of laser induced periodic surface structures (LIPSS) on stainless steel. More specifically, the topography and maximum depth of LIPSS trenches are theoretically and experimentally investigated as a function of the number of laser pulses. Moreover, precise LIPSS morphology measurements are performed using atomic force microscopy (AFM). The proposed comprehensive simulation study is based on two-temperature model (TTM) non-equilibrium thermal simulations coupled with fluid dynamic computations to capture the melting metal phase occurring during FLSP. Our rigorous simulation results are found to be in excellent agreement with the AFM measurements. The presented theoretical framework to model FLSP under low-fluence femtosecond laser pulses will be beneficial to various emerging applications of LIPSS on metallic surfaces, such as cooling high-powered laser diodes and controlling the thermal emission or absorption of metals.

Rapid fabrication of antireflective structures on ZnS surface by spatial shaping femtosecond laser

Antireflection performance and fabrication efficiency are key factors that affect the practical application of antireflective structures. Nowadays, how to combine good antireflection performance with highly efficient processing is still a difficult problem. In this work, a novel and scalable method of fabrication of antireflective LIPSS (laser induced periodic surface structure) on ZnS surface by spatial shaping femtosecond laser is proposed. A Gaussian beam is converted to a line beam by a cylindrical lens transformation. The focal long axis of line beam is on the scale of centimeters, and the minor axis is on the scale of micrometers. Hence, the fabrication efficiency can be significantly improved by adjusting the scanning direction perpendicular to the major axis. Notably, the proposed highly efficient method only takes 21 s to complete the fabrication of 1 × 1 cm2 antireflective ZnS surface with excellent antireflective property. At the laser power of 500 mW, scan speed of 1.0 mm/s, scan interval of 0.55 cm, the transmittance of fabricated antireflective structures maintains 78–87.5% at 2.5–10 μm, with the average transmittance of 81.3%, 5.9% higher than that of untreated ZnS. This proposed method may open a revolutionary concept for the rapid antireflective surface laser processing, which has a great application potential in energy, military, aerospace and other fields.