Interference Patterning Technique Research Articles

Fabrication of functional zirconia surfaces using a two‐beam interference setup employing a picosecond laser system with 532‐nm wavelength: Morphology, microstructure, and wettability

AbstractThe aim of this work was to evaluate the feasibility of the fabrication of microtextures in zirconia using the direct laser interference patterning (DLIP) technique. A green ultra‐short pulsed laser (532 nm, 10 ps) with a two‐beam interference setup was used to produce line‐like structures with a spatial period of 3 µm. For a fixed set of fluence and pulse‐to‐pulse overlap values (6.2 J/cm2, 81%), periodic structures were successfully created for different hatch distances. The average depth of the features ranged from 0.37 µm for a hatch distance of 14.4 µm up to 0.84 µm for a hatch distance of 12.4 µm. However, a further decrease in hatch distance did not result in an increase in depth since the region of the ridges is also ablated. Scanning electron microscopy analysis showed pores formation on the laser grooves, but no sign of micro‐cracking could be observed. Wettability tests showed an increase in hydrophobicity after DLIP. These results bring exciting perspectives on the fabrication of micro‐textures with DLIP on zirconia surface.

Ink‐Assisted Laser‐Induced Heterogeneous Permanent/Erasable Nanostructures on Metals

AbstractStructural color fabrication attracting significant interest for science and art is usually restricted by costly and time‐consuming structuring processes or inerasable characteristics of structures. Herein, by developing a universal, low‐cost technical solution—the nanosecond laser irradiation of ink (Solvent Black 7) layers coated on metal—laser‐induced heterogeneous permanent/erasable nanostructures (LIHPEN) are produced successfully on multiple metals, especially noble metals, without ablation damage to intrinsic surfaces. LIHPEN consist of uniform laser‐induced periodic surface structures produced by surface plasmon polariton excitation of metals and can be extended into 2D hybrid micro/nanostructures by introducing the direct laser interference patterning technique. LIHPEN technology operated under a large processing parameter window can realize space‐selective erasability of prepared structures by controlling processing parameters, which determine the ink‐layer carbonization degree and thus the permanent or erasable characteristic. Because ink layers can be coated manually, in addition to realizing digital scanning patterns, LIHPEN technology can be integrated with traditional artistic techniques to solidify and color artworks without risk of information loss and leakage in digital copying. LIHPEN with good durability can exhibit vivid structural colors on metals, demonstrating its great potential in fields of artwork iridescent coloring, encryption, and anti‐counterfeiting, particularly those requiring customization, personalization, and rewritability.

Laser structuring with DLIP technology of tungsten carbide with different binder content

In machining, tool wear is one of the main influence factors for the resulting quality of the product. Several wear mechanisms have to be addressed to prevent unwanted deterioration of the tool integrity. For aluminium alloys, adhesion of the workpiece material on the cutting tool is one of the most challenging wear mechanisms. Engineering surface microtopographies has been proved as a convenient strategy to tackle this issue. Particularly, the direct laser interference patterning (DLIP) technique enables the integration of periodic structures on the micrometer or sub-micrometer scale. In this study the structuring of tungsten carbide with different cobalt content is presented. The interference of two laser beams leads to periodic line-like structures with a spatial period of 5.5 µm. A maximum structure depth of 2.2 µm is reached by controlling the processing parameters. Moreover, the wettability of the structured samples was analyzed by contact angle measurements with selected cooling lubricants, revealing a hydrophilic behavior with a decreased contact angle of 10°. This work gives an insight into the possibilities of structuring tungsten carbide materials with a picosecond laser source in combination with an innovative beam shaping setup from the point of view of an analysis to explore the formation of structured surfaces and their wetting behavior with cooling lubricants.

Simultaneous Micro-Structuring and Surface Smoothing of Additive Manufactured Parts Using DLIP Technique and Its Influence on the Wetting Behaviour.

It is well known that the surface topography of a part can affect its function as well as its mechanical performance. In this context, we report on the surface modification of additive manufactured components made of Titanium 64 and Scalmalloy®, using Direct Laser Interference Patterning technique. In our experiments, a nanosecond-pulsed near-infrared laser source with a pulse duration of 10 ns was used. By varying the process parameters, periodic structures with different depths and associated roughness values are produced. Additionally, the influence of the resultant morphological characteristics on the wettability behaviour of the fabricated textures is investigated by means of contact angle measurements. The results demonstrated a reduction of the surface roughness of the additive manufactured parts (in the order of some tens of micrometres) and simultaneously the production of well-defined micro-patterns (in the micrometre range), which allow the wettability of the surfaces from 26° and 16° up to 93° and 131° to be tuned for Titanium 6Al 4V and Al-Mg-Sc (Scalmalloy®), respectively.

Tailored wetting of copper using precise nanosecond direct laser interference patterning

Nowadays, functionalized surfaces become more and more important for industrial applications concerning wettability, ice-repellency, self-cleaning, or tribology. In this contribution, an innovative approach is presented using the direct laser interference patterning (DLIP) technique for tailoring the wettability of copper surfaces. The interference of the laser beams was conducted by using prisms for forming a like-like pattern with a spatial period Λ of 3.3 µm. Moreover, texture depths up to 1.01 µm were reached. The wettability could be set to static water contact angles between 120° and 150° This paper gives inside into the viability of structuring copper materials using a low-cost nanosecond laser source in combination with an innovative beam shaping setup.

Direct Laser Interference Patterning of Bioceramics: A Short Review

Bioceramics are a great alternative to use in implants due to their excellent biocompatibility and good mechanical properties. Depending on their composition, bioceramics can be classified into bioinert and bioactive, which relate to their interaction with the surrounding living tissue. Surface morphology also has great influence on the implant biological behavior. Controlled texturing can improve osseointegration and reduce biofilm formation. Among the techniques to produce nano- and micropatterns, laser texturing has shown promising results due to its excellent accuracy and reproducibility. In this work, the use of laser techniques to improve surface morphology of biomaterials is reviewed, focusing on the application of direct laser interference patterning (DLIP) technique in bioceramics.

Micropatterning of fluorescent silver nanoclusters in polymer films by Laser Interference

Hybrid films of poly (methacrylic acid) (PMAA) and silver fluorescent nanoclusters were structured by the Direct Laser Interference Patterning technique (DLIP) using few nanosecond laser pulses (355 nm) to obtain an arranged and well-defined periodic surface pattern. It is shown that the films of neat PMAA are not structured by irradiation at 355 nm due to its low absorbance at this wavelength. However, the silver nanoclusters act as chromophores increasing the absorbance of the film and allowing the surface patterning. Also, the interaction of the laser beam with a film of PMAA doped with Ag+ induces the formation of fluorescent silver nanoclusters and the subsequent surface patterning. The patterned films maintain the luminescent properties of the PMAA/Ag nanoclusters in solution. The structured and unstructured films were characterized by optical, atomic force and spectral laser confocal scanning microscopy showing highly oriented lines patterning already after just one laser pulse.

Direct laser interference patterning of ophthalmic polydimethylsiloxane (PDMS) polymers

The inscription of diffractive elements in ophthalmic polymers and ocular tissues to induce refractive index changes is of great interest in the fields of Optics and Ophthalmology. In this work fabrication of linear periodic patterns in polydimethylsiloxane (PDMS) intraocular lenses by means of the direct laser interference patterning (DLIP) technique was studied. A Q-Switch Nd:YAG laser coupled to second and third harmonic modules emitting linearly polarized 4 ns pulses at 355 nm with 20 Hz repetition rate was used as the laser source. Laser processing parameters were modified to produce the linear patterns. Processed samples were characterized by means of optical confocal microscopy, Scanning Electron Microscopy SEM, Energy Dispersive X-ray Spectroscopy EDX, Attenuated Total Reflectance-Infrared Spectroscopy ATR-FTIR, and Raman Spectroscopy. Depending on the laser parameters both photo-thermal and photo-chemical damage were observed in the DLIP irradiated areas. Finally, diffractive techniques were used to characterize the diffraction gratings inscribed in the samples resulting in a refractive index change of 1.9 × 10−2 under illumination of a 632.8 nm He-Ne laser.

Frictional Performance Assessment of Cemented Carbide Surfaces Textured by Laser

Cemented carbides are advanced engineering materials often used in industry for manufacturing cutting tools or supporting parts in tribological system. In order to improve service life, special attention has been paid to change surface conditions by means of different methods, since surface modification can be beneficial to reduce the friction between the contact surfaces as well as to avoid unintended damage. Laser surface texturing is one of the newly developed surface modification methods. It has been successfully introduced to fabricate some basic patterns on cemented carbide surfaces. In this work, Direct Laser Interference Patterning Technique (DLIP) is implemented to produce special line-like patterns on a cobalt (Co) and nickel (Ni) based cemented tungsten carbide grade. It is proven that the laser-produced patterns have high geometrical precision and quality stability. Furthermore, tribology testing using a nano-tribometer unit shows that friction is reduced by the line-like patterns, as compared to the polished one, under both lubricated and dry testing regimes, and the reduction is more pronounced in the latter case.

Laser microstructured metal thin films as promising alternative for indium based transparent electrodes.

In the search for alternative materials to replace indium-tin-oxide in transparent electrodes we have structured copper and aluminum thin films (between 5 an 40 nm) for tailoring their optical properties. Micrometer scaled holes were produced using the direct laser interference patterning (DLIP) technique. We compared the optical and electrical parameters of nanosecond and picosecond processed thin films. It was found that the optical transmittance of the structured layers was relatively increased between 25 to 125% while the electrical resistance was marginally influenced. In addition, the laser treatment enhanced the diffuse to total transmission ratio (HAZE) by values ranging from 30 to 82% (relative) as a potential advantage of μm structuring. The results also show that both of the studied metals succeed to match the target which is set by typical applications of indium thin oxide (ITO) films. Furthermore, numerical simulations are performed in order to understand the ablation process of thin film material for ps and ns pulses.

Effect of laser-induced conversion of silicon nitride to silicon oxy-nitride on antireflective properties of passivation layer in polysilicon solar cells

Silicon solar cell technology is dominating in the photovoltaic industry, however, a further increase in cost-effectiveness is needed. This can be achieved by increasing the light coupling in the active layer of the cell. Passivation layer of the commercial polycrystalline silicon solar cells was textured using the laser beam interference patterning technique to obtain enhanced optical properties due to the formation of periodic refractive index grating. As a consequence of laser irradiation, passivation layer of silicon nitride was partially oxidized at the intensity peaks of the interference distribution. Periodic distribution of oxidized areas was found by EDS. Investigation of optical and electrical properties of the laser treated solar cells shows increased light coupling and better photo-electrical performance. Simulations were carried out to evaluate the influence of refractive index grating formed in silicon oxy-nitride to optical properties of the patterned solar cells. Periodic oxide grating was found to be more efficient for light coupling in thinner film structures. The results of this work may find applications in other fields as it allows alteration of material composition in the well-defined periodic pattern.

Holographically Fabricated Dye-Doped Nanoporous Polymers as Matrix for Laser Desorption/Ionization Mass Spectrometry

We report laser desorption/ionization mass spectrometry using a dye-doped nanoporous polymer matrix. The nanoporous polymer matrix was fabricated through a holographic interference patterning technique. The periodically aligned nanopores in the resulting polymer matrix produced a high surface-to-volume ratio that facilitates the homogeneous cocrystallization of the matrix and an analyte (i.e., peptide in this demonstration). To generate nanostructures with further enhanced functionalities, dyes were also incorporated into the photopolymer. We demonstrate that by using the dye-doped nanoporous polymer matrix, we can identify peptides with an enhanced signal from the peptides and decreased noise from the ion fragmentation. These results indicate that the dye-doped nanoporous polymer matrix we use here can be a promising platform for laser desorption/ionization mass spectrometry.

Direct laser interference patterning of multi-walled carbon nanotube-based transparent conductive coatings

Topographical structures were created on the surface of multi-walled carbon nanotube-based coatings deposited on borosilicate glass using the direct laser interference patterning (DLIP) technique. Films made by multi-walled carbon nanotubes (MWNTs) dispersed in antimony-doped tin oxide (ATO) matrix and networks of MWNTs with both low and high adherence to the substrates were irradiated with one single laser pulse. Due to the high absorption coefficient of ATO, the film was completely removed at the interference maxima positions leading to periodic arrays of high quality on macroscopic areas. Additionally, increase of the laser fluence has produced wider ablated regions. Irradiation of high adherent networks of MWNTs produced a periodic porous structure, what has been attributed to the presence of adherence promoters in the film. On the other hand, MWNT networks with low adhesion to the substrate were strongly removed at the interference maxima positions. In this case, however, the fabricated periodic structures presented several defects that result from the poor adherence of the film to the substrate.

Humidity sensing based on nanoporous polymeric photonic crystals

In this work, an optical humidity sensor based on a nanoporous polymeric photonic crystal (PC) is demonstrated. The PC sensing structure is created by combining a holographic interference patterning technique with a modified holographic polymer-dispersed liquid crystal system. Changes in relative humidity (RH) induce the modification of the refractive index contrast between the nanoporous and nonporous regions, and thus the transmittance and bandgap position, of the PC structure. For a PC structure with 30% porosity and a grating spacing of 220 nm, a change in the RH from 40% to 95% at 34 °C results in a redshift of 43 nm in the central wavelength at the PC bandgap and an increase from 12% to 87% in the relative transmittance at λ = 600 nm. Other performance analyses have shown that the nanoporous polymeric PC-based humidity sensor is highly stable and reproducible, exhibits minimal hysteresis, and responds relatively fast.