Laser-induced Periodic Structures Research Articles

Ultrafast dynamics of femtosecond laser-induced high spatial frequency periodic structures on silicon surfaces

Ultrafast dynamics of femtosecond laser-induced high spatial frequency periodic structures on silicon surfaces

Formation of Laser-Induced Periodic Structures on Thin Films of Transition Metal and Semiconductor Nitrides

Formation of Laser-Induced Periodic Structures on Thin Films of Transition Metal and Semiconductor Nitrides

Highly regular laser-induced periodic silicon surface modified by MXene and ALD TiO2 for organic pollutants degradation

The co-catalytic ability of surface groups in MXene renders MXene-based composites efficient photocatalysts for organic dye photodegradation. In this study, we introduce a novel approach combining highly-regular laser-induced periodic surface Si structures (Si nanoripples - SiNR) with MXene and TiO2, deposited through atomic layer deposition (ALD), to achieve stable, repeatable, and highly efficient photocatalytic materials. The ternary system, SiNR/MXene/TiO2, exhibits high light absorption across the entire spectrum. Furthermore, the photodegradation efficiency of SiNR/MXene/TiO2 is approximately 2.6 times higher than that of SiNR/TiO2 samples. This remarkable enhancement in photocatalytic activity can be attributed to two main factors: increased separation of photogenerated charge carriers and enhanced light absorbance through the light trapping effect. The synergistic combination of SiNRs, MXene, and TiO2 in the ternary nanocomposite structure enables efficient separation of photogenerated charge carriers, thereby minimizing recombination and enhancing the degradation of organic dyes. Moreover, the introduction of a laser-patterned surface and its ALD modification significantly enhances light absorbance, ensuring effective utilization of a wider range of the solar spectrum for photocatalysis. Therefore, SiNR/MXene/TiO2 ternary nanocomposites hold great promise for developing high-performance photocatalysts for water purification applications, offering improved stability, repeatability, and enhanced photocatalytic efficiency.

Impact of film thickness in laser-induced periodic structures on amorphous Si films

We report self-organized periodic nanostructures on amorphous silicon thin films by femtosecond laser-induced oxidation. The dependence of structural periodicity on the thickness of silicon films and the substrate materials is investigated. The results reveal that when silicon film is 200 nm, the period of self-organized nanostructures is close to the laser wavelength and is insensitive to the substrates. In contrast, when the silicon film is 50 nm, the period of nanostructures is much shorter than the laser wavelength, and is dependent on the substrates. Furthermore, we demonstrate that, for the thick silicon films, quasi-cylindrical waves dominate the formation of periodic nanostructures, while for the thin silicon films, the formation originates from slab waveguide modes. Finite-difference time-domain method-based numerical simulations support the experimental discoveries.Graphical abstract

Formation of Sub-100 nm Femtosecond Laser-Induced Periodic Fine Structures on Laser Powder Bed Fusion Fabricated Stainless Steel

Formation of Sub-100 nm Femtosecond Laser-Induced Periodic Fine Structures on Laser Powder Bed Fusion Fabricated Stainless Steel

Micro/nanostructured amorphous TiNbZr films to enhance the adhesion strength and corrosion behavior of stainless steel

To improve the corrosion resistance of key components and ensure the service safety of marine equipment, here we combined femtosecond (fs) laser fabrication and magnetron sputtering deposition to develop micro/nanostructured amorphous TiNbZr films. Analysis of the compositional, microstructural, corrosion, and mechanical properties was conducted. The results showed that the TiNbZr films were amorphous, and spherical TiNbZr nanoparticles uniformly covered the fs laser-induced periodic fringe structure. A complex hierarchical micro/nanostructure was formed that was hydrophobic and showed enhanced adhesion strength. The TiNbZr films deposited on fs laser-treated substrates provided the best corrosion resistance, showing a self-corrosion current density of 116 nA/cm2, excellent passive ability, and pitting resistance. The microscratch test revealed that the micro/nanostructures doubled the binding strength of the TiNbZr/316L interface due to the compositional and structural gradients induced by an approximately 20 nm transition layer formed during fs laser processing. This work provides a new method for obtaining anti-corrosion films with a high adhesion strength for marine applications.

Laser-induced periodic surface structuring for secondary electron yield reduction of copper: dependence on ambient gas and wavelength

One of the main limitations for future high-performance accelerators operating with positively charged particles is the formation of an electron-cloud inside the beam vacuum chamber, giving rise to instabilities. The Secondary Electron Yield (SEY) of the beam-facing surfaces gives a measure of the mechanism which drives this phenomenon. The laser-induced periodic structure formation on Cu surfaces has been demonstrated as a promising process to reduce SEY. In view of applications in beam chambers, we studied the laser process influence on SEY for 515 and 1030 nm wavelength femtosecond pulses on copper in different ambiences (air, nitrogen, vacuum). Depending on used process conditions, the surface composition differs, structures with varying aspect ratio are formed, i.e., periodic ripples and large-scale channels. Treatment in air at 515 nm is the most efficient for the formation of deeper structures allowing SEY maximum reduction first down to 1.6–1.7 and then below unity upon electron irradiation, thereby totally suppressing electron-cloud. Increasing the laser fluence, SEY will further reduce due to surface roughness enhancement via nanoparticle redeposition. This study reveals the fundamental role of LIPSS treatments to enable surface treatment in large-scale accelerator installations, where particle-free components are desired, and paves the way to potential future applications.

Ionization dynamics and damage conditions in fused silica irradiated with mid-infrared femtosecond pulses

The employment of ultrashort laser sources at the mid-infrared (mid-IR) spectral region for dielectrics is expected to open innovative routes for laser patterning and a wealth of exciting applications in optics and photonics. To elucidate the material response to irradiation with mid-IR laser sources, a consistent analysis of the interaction of long wavelength femtosecond pulses with dielectric materials is presented. The influence of the pulse duration is particularly emphasized in specifying the laser parameters for which photoionization and impact ionization are important. Simulation results using pulses at 2.2, 3.2, and 5 μm are conducted to illustrate optimum conditions for the onset of damage on the solid that is related to the occurrence of the optical breakdown. The results predict that the damage threshold scales as ∼τpa (0.31≤a≤0.37) at all laser wavelengths. Given the significant effect of the induced excitation level on excitation of surface plasmons (SPs), which account for the formation of laser-induced periodic structures oriented perpendicular to the laser polarization, a correlation of the produced electron densities with SPs and the threshold of SP excitation (∼τpβ, 0.33≤β≤0.39) are also discussed in this as yet unexplored spectral region. The results are expected to guide development of an innovative approach to surface patterning using strong mid-IR pulses for advanced applications.

Comparing study on single-beam and two-beam interference scanning for nanosecond laser-induced periodic structures on chromium metal

Comparing study on single-beam and two-beam interference scanning for nanosecond laser-induced periodic structures on chromium metal

Design and fabrication of micro and nano surface structures for enhancing metal–polymer adhesion using femtosecond laser treatment

This study investigated the effects of micro- and nanostructures on the adhesion strength between copper and an encapsulating mold compound (EMC). The shape of the microgrooves was designed based on fracture mechanics theory, and the effect of laser-induced periodic structure surface (LIPSS) formation on the microgroove was investigated using numerical simulations. The designed surface profiles were fabricated using femtosecond laser treatments, and the adhesion strength between copper and the EMC was evaluated. The results show that deep microgrooves improved the adhesion strength owing to the anchor effect. However, the aspect ratio between the pitch and depth of the microgroove had a limitation in enhancing the adhesion strength. The formation of LIPSSs on the mountaintop of the microgroove was very effective; however, an LIPSS on the valley of the microgroove was ineffective. Numerical analyses revealed that LIPSSs suppressed the shear deformation of the EMC and worked as resistance to interface delamination. Based on the findings obtained in this study, combining micro- and nano-scale surface structure formation with femtosecond laser treatments is an effective and eco-friendly method for improving adhesion strength.

Threshold effect on the femtosecond laser-induced periodic subwavelength structure: An analytical approach

For linearly polarized femtosecond laser-induced periodic nanostructures on a metal surface, the underlying physics of self-formation patterns is yet to be fully explained. We demonstrated here that the stabilized periodic interface electrostatic field (Coulomb field) arising from the surface phase-locking resonant dominates the self-formation of ripple structures. The kinetics of ultrafast laser ablation on solid surface were discussed. The threshold fluence and upper limit fluence for self-formation of ripple structures were calculated. The underlying mechanisms were clarified with both simulation and experimental results. Analytical formula for the interspace between ripples (i.e., wavelength of surface Langmuir wave) was developed. As illustrated by the experimental results, the competition of the two ablation mechanisms, namely surface Coulomb ablation and direct ultrafast laser ablations, was shown to result in distinct structuring patterns for a typical Gaussian pulse laser irradiation on the target surface at the appropriate laser energy fluence.

Laser-Processed PEN with Au Nanowires Array: A Biocompatibility Assessment

Although many noble metals are known for their antibacterial properties against the most common pathogens, such as Escherichia coli and Staphylococcus epidermidis, their effect on healthy cells can be toxic. For this reason, the choice of metals that preserve the antibacterial effect while being biocompatible with health cells is very important. This work aims to validate the effect of gold on the biocompatibility of Au/Ag nanowires, as assessed in our previous study. Polyethylene naphthalate (PEN) was treated with a KrF excimer laser to provide specific laser-induced periodic structures. Then, Au was deposited onto the modified PEN via a vacuum evaporation method. Atomic force microscopy and scanning electron microscopy revealed the dependence of the surface morphology on the incidence angle of the laser beam. A resazurin assay cytotoxicity test confirmed safety against healthy human cells and even cell proliferation was observed after 72 h of incubation. We have obtained satisfactory results, demonstrating that monometallic Au nanowires can be applied in biomedical applications and provide the biocompatibility of bimetallic Au/AgNWs.

Effects of Ablation Regimes on the Formation and Evolution of Femtosecond Laser-Induced Periodic Structures on Titanium

The formation and evolution of laser-induced periodic structures (LIPSS) have attracted much attention due to their broad applications and rich physics. The literature has shown that excessive laser energy accumulation, such as increasing single pulse energy or cumulative pulse number on a sample, leads to a final fuzzy LIPSS period or even disappearance of the period. This article discovers a new phenomenon by increasing the laser fluence; the periodic structure appears blurred and disappears in the middle of the laser fluence region. Two contrary evolution tendencies of the period’s disappearance are observed for the first time. This phenomenon can be attributed to femtosecond ablation regimes in different fluence regions. The experimental results and discussion provide a powerful guarantee for the high-quality preparation of structures by controlling the experimental parameters for future practical applications. The findings of this study play a significant role in regulating the LIPSS period and provide ideas for avoiding the hidden danger of the cycle structure disappearing during the creation of the LIPSS structure, which has practical implications for future LIPSS applications.

Transformation from nano-ripples to nano-triangle arrays and their orientation control on titanium surfaces by using orthogonally polarized femtosecond laser double-pulse sequences

One-dimensional and two-dimensional laser-induced periodic structures (nano-ripples and nano-triangle arrays) are fabricated on titanium surfaces by direct scanning with orthogonally polarized and equal-energy femtosecond laser double-pulse sequences (OP pulses). Clear and regular nano-ripples and nano-triangle arrays are formed when the laser fluence is slightly higher than the ablation threshold of titanium and the time delay is approximately 2 ps or shorter. By changing only the scanning speed, we achieve the transformation from nano-ripples to nano-triangle arrays. The orientation of nano-ripples and that of one of the three sides of nano-triangle arrays are always perpendicular to the scanning direction rather than the laser polarization. The mechanism underlying this phenomenon is as follows. First, the nano-ripples are formed due to periodic energy deposition along the direction of surface waves (surface plasmon polaritons; SPPs), which is along the scanning direction during the scan process. Subsequently, the preformed nano-ripples irradiated with subsequent laser pulses undergo hexagonal convection flow and are transformed into nano-triangle arrays. The preformed nano-ripples perpendicular to the scanning direction have a positioning effect on the formation of nano-triangle arrays, as verified in two-step fast scan experiments. Large-area patterning of nano-triangle arrays producing three-directional structural color is demonstrated in this paper.

Regulating Morphology and Composition of Laser-Induced Periodic Structures on Titanium Films with Femtosecond Laser Wavelength and Ambient Environment.

Recently, highly uniform thermochemical laser-induced periodic surface structures (TLIPSS) have attracted significant research attention due to their practical applicability for upscalable fabrication of periodic surface morphologies important for surface functionalization, diffraction optics, sensors, etc. When processed by femtosecond (fs) laser pulses in oxygen-containing environments, TLIPSS are formed on the material surface as parallel protrusions upon local oxidation in the maxima of the periodic intensity pattern coming from interference of the incident and scattered waves. From an application point of view, it is important to control both the TLIPSS period and nanoscale morphology of the formed protrusions that can be expectedly achieved by scalable shrinkage of the laser-processing wavelength as well as by varying the ambient environment. However, so far, the fabrication of uniform TLIPSS was reported only for near-IR wavelength in air. In this work, TLIPSS formation on the surface of titanium (Ti) films was systematically studied using near-IR (1026 nm), visible (513 nm) and UV (256 nm) wavelengths revealing linear scalability of the protrusion period versus the fs-laser wavelength. By changing the ambient environment from air to vacuum (10−2 atm) and pressurized nitrogen gas (2.5 atm) we demonstrate tunability of the composition and morphology of the Ti TLIPSS protrusions. In particular, Raman spectroscopy revealed formation of TiN together with dominating TiO2 (rutile phase) in the TLIPSS protrusions produced in the nitrogen-rich atmosphere.

Surface modification of titanium alloy via atmospheric pressure nitrogen plasma assisted femtosecond laser irradiation

The effect of atmospheric pressure nitrogen plasma in conjunction with femtosecond laser surface modification of Ti–6Al–4V samples was investigated. It was suggested that the superior friction and wear characteristics of the LP series (the sample subjected to both laser and plasma irradiation) were induced by the synergistic combination of the following three factors: the increased smoothness induced by homogenizing the laser-induced periodic surface groove shape structure, the high hardness caused by grain refinement and the high toughness and low friction properties conferred to the sample by the formation of oxynitride.

Femtosecond laser-induced periodic structures: mechanisms, techniques, and applications

Over the past two decades, femtosecond laser-induced periodic structures (femtosecond-LIPSs) have become ubiquitous in a variety of materials, including metals, semiconductors, dielectrics, and polymers. Femtosecond-LIPSs have become a useful laser processing method, with broad prospects in adjusting material properties such as structural color, data storage, light absorption, and luminescence. This review discusses the formation mechanism of LIPSs, specifically the LIPS formation processes based on the pump-probe imaging method. The pulse shaping of a femtosecond laser in terms of the time/frequency, polarization, and spatial distribution is an efficient method for fabricating high-quality LIPSs. Various LIPS applications are also briefly introduced. The last part of this paper discusses the LIPS formation mechanism, as well as the high-efficiency and high-quality processing of LIPSs using shaped ultrafast lasers and their applications.

Nanosecond laser-induced periodic structures on polyimide film

Nanosecond laser-induced periodic structures on polyimide film

Formation of laser-induced periodic structures on thin films of transition metal nitrides

Formation of laser-induced periodic structures on thin films of transition metal nitrides

Crystal cleavage, periodic nanostructure and surface modification of SiC ablated by femtosecond laser in different media

SiC , as one typical 3rd generation semiconductor, has high potential to be used as the substrate for harsh environment sensors. However, the etching of this material is still challenging. Femtosecond laser has been demonstrated to have great potential in SiC etching, but the material removal mechanisms need further investigation. Herein, the two-temperature model considering carrier concentration is utilized to illustrate the microscopic mechanism of carrier concentration and temperature change in SiC caused by femtosecond laser irradiation. An 800 nm, 50 fs, 10 Hz Ti: sapphire femtosecond laser was used to process SiC in different media including air, HF and water. The ablation threshold of SiC in the three media is calculated. The highest ablation threshold (4.98 J/cm 2 ) is obtained when the pulse number N = 50, in air. The lowest ablation threshold (0.53 J/cm 2 ) is obtained when the pulse number N = 300, in HF. Results indicate that ablation threshold is strongly dependent on the laser pulse number and processing medium. Based on the cleavage phenomenon of SiC crystal structure observed by micro-nano characterization, the mechanism model of femtosecond laser-induced periodic structure of SiC surface based on material lattice cleavage is established, and the relationship between the intrinsic texture and the evolution of periodic structure of ablation surface is revealed. This will provide a new way to understand the ablation mechanism of femtosecond laser. In addition, the processing media has significant effect on surface roughness and chemical bond characteristics of SiC. Liquid processing media can reduce the surface roughness and avoid oxidation, which is helpful to manufacture SiC devices with specific surface requirements using femtosecond laser as an auxiliary method. • The mechanism of femtosecond laser ablating SiC in different media are studied systematically. • The ablation threshold of SiC in different media (air, water, HF) are experimentally obtained. • The femtosecond laser-induced periodic structure is closely related to intrinsic structure cleavage.