14 research outputs found
The fabrication of hydrophilic structure on lens via direct laser interference lithography
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Influence of aluminum addition on the laser powder bed fusion of copper-aluminum mixtures
No full textThe high optical reflectivity of copper (Cu) in the near infrared (NIR) domain and its elevated heat dissipation make Cu a challenging metal for laser powder bed fusion (LPBF), even with high energy densities (EDs). In this study, we demonstrated that adding aluminum (Al) powder by as little as 0.75, 1.5, and 3 wt.% substantially enhances Cu processability, leading to denser (up to 98 %) and smoother (Ra = 3.3 μm) Cu-Al parts as compared to 95% and 18 μm, respectively, for the parts printed using pure Cu. In addition, this method reduces the ED required by a factor of two for the additive manufacturing of the Cu-based parts while maintaining a significant heat dissipation. These improvements are achieved due to the coexistence of solid Cu particles with liquid Al at the vicinity of the molten pool, accomodating the predensification of the powder mixture. The development of the semi-liquid 3D printing 2 approach opens up a new path to easily print materials difficult to be printed for broadening their applications
Chemical element variation in fungi-induced coating degradation using laser-induced breakdown spectroscopy combined with Raman spectroscopy, mass spectrometry, and multivariate analyses
No full textInternational audienceTraditional coating products for hindering fungal growth are environmentally hazardous. As regulations become increasingly stringent, environmentally benign coating materials are becoming more prevalent. However, due to these new, lower-toxicity coating materials, the growth of mold, mildew, and other fungus begins to cause detrimental effects on materials. Thus, it is important to develop an understanding of the fungal survival and material degradation mechanisms of such low-toxicity coating materials. This study explored the fungal degradation mechanisms of coating materials by developing an approach combining laser-induced breakdown spectroscopy (LIBS), Raman spectroscopy, and mass spectrometry (MS). The coating systems tested in this study were MIL-PRF-23377, Type I, with chromate (class C) and non-chromate (class N). Aspergillus niger (A. niger) was used for fungal growth. The LIBS results indicate a chemical change/exchange (Mg, Ca, Ti, C, and N) during fungi-induced corrosion. In the Raman study, chemical bond changes at Raman peaks 748, 812, 976, 1006, 1041, 1184, and 1610 cm−1 were identified in the class N coatings after fungal growth. In the MS study, organic acids (oxalic and acetic) produced by fungi were detected. Based on the results, degradation mechanisms of non-Cr coating materials were proposed
Forming three-dimensional micro-objects using two-dimensional gradient printing
No full textControllable transformations from two-dimensional (2D) patterns to three-dimensional (3D) geometries independent of materials or external stimuli are being pursued in numerous fields. Here, we present an approach to forming various 3D structures through 2D printing using distributed stress inside a polymer. The key is to establish controlled stress fields by introducing composition and property gradients inside a photocurable polymer by femtosecond laser two-photon polymerization. Structural deformation induced by internal stress is a general bottleneck both in materials processing and 3D printing. In contrast to the significant efforts previously made to reduce stress and deformation, we use them to enable shape transformation to construct various 3D micro-objects through 2D printing with engineered stress fields inside. Multi-mode 2D-to-3D structural transformations, including bending, rolling, coiling, waving, spiraling, and out-of-plane distortions are realized in a shape- and location-specific fashion. This strategy promises a unique way to fabricate delicate 3D objects not feasible through conventional techniques and to circumvent the intrinsic stepping limitations in direct 3D printing using two-photon polymerization. When combined with the standard 2D patterning techniques such as nanoimprint and photolithography, such a 2D-to-3D transformation approach will lay a foundation for high-throughput and cost-effective production of complex 3D nanostructures
Femtosecond laser polishing of pure copper surfaces with perpendicular incidence
No full textOver the past few years, femtosecond (fs) laser processing has drawn a growing interest in a wide range of applications as it offers the possibility to process the surface morphologies of metals and semiconductors. In contrast to other polishing techniques, laser polishing offers a flexible and non-contact solution, thereby avoiding potential external contamination, while enabling a precise selection of processing areas. We investigated the influence of fs laser parameters on surface roughness of pure copper and ablation thickness, focusing on highlighting the importance of fluence and scanning overlap. With a two-step processing strategy, composed of coarse and fine polishing steps, surfaces with Sa < 400 nm were achieved, representing a 98% reduction from the high roughness of 15 μm on initial surfaces. This research demonstrated the possibility of directly polishing rough parts using a fs laser with a perpendicular incidence. © 202
Time-resolved imaging of microscale dynamics in laser drying of silicon wafers
No full textSurface drying plays a critical role in wafer fabrication in microelectronics, primarily on eliminating watermarks. Spin drying, isopropanol alcohol (IPA) drying, and Marangoni drying are the most commonly used methods, but they have drawbacks such as high risk of water stains, safety hazards, environmental concerns, and energy inefficiency. Hence, there is a continuous demand for fast, efficient, chemical-free, and energy-efficient wafer drying processes. This study explored the use of nanosecond (ns) laser pulses for laser-induced sub-surface evaporation as a promising alternative for surface drying. By adjusting the laser fluence, clean and dry silicon (Si) substrates can be obtained without any stain or damage. Large-area laser drying was also demonstrated. Time-resolved imaging was employed to investigate the drying dynamics after the interaction between the laser pulses and the substrates. It was observed that the deposited water droplet films expand, detach from the substrates, and eject into the air after excimer laser pulses. Moreover, the study examined the influence of substrate conditions on laser drying, including surface roughness and hydrophilicity. The effectiveness of laser drying was evaluated on various substrates, including stainless steels (polished/mirror polished) and glasses. Pulsed lasers demonstrate the ability to dry chemical solutions, such as 35 g/L NaCl, in addition to pure water. These findings show the potential of using ns pulsed lasers as a versatile and environmentally friendly drying tool for various solution and substrate types
Non-sticky superhydrophobicity on polypropylene surfaces achieved via single-step femtosecond laser-induced processing in n-hexadecane liquid
No full textInternational audienceThe preparation of superhydrophobic polypropylene (PP) surfaces for biosafety is a pressing challenge in the food and medical industries. We achieve superhydrophobicity on commercial PP using a single-step process based on femtosecond (fs) laser-induced micro/nano texturing in n-hexadecane. Analysis of the wetting behavior after fs laser texturing revealed that 120 times of repetitive texturing, with a contact angle (CA) exceeding 150° and a rolling angle below 1° yielded optimal results. The generation, growth, and evolution of micro/nanostructures over processing times were investigated to establish a direct correlation between the micro/nanostructures and hydrophobicity. Furthermore, we elucidated the interactions between fs laser pulses and different material types in air, water, and n-hexadecane to explain the formation of micro/nanostructures formed in n-hexadecane
Laser powder bed fusion of diamond‐reinforced AlSi10Mg: printing process, interfacial characterization, and mechanical properties
No full textInternational audienceThe additive manufacturing of metal matrix composites (MMCs) using laser powder bed fusion (LPBF) is gaining considerable attention for its ability to produce high‐performance materials with intricate geometries. However, incorporating reinforcement such as diamond (D) particles poses challenges to the melting and solidification behavior of the powders, potentially affecting print quality. In this study, the laser irradiation of AlSi10Mg powder mixed with 5 vol% of uncoated D particles is investigated across varying processing parameters. Dense (97%) and crack‐free parts are successfully produced using high laser powers (300 and 400 W) and low laser scanning speeds (300 and 400 mm s −1 ). It is shown that the energy needed for proper melting of the powder surpasses that required for printing pure AlSi10Mg. Scanning transmission electron microscopy coupled with energy‐dispersive X‐ray spectroscopy uncovers a direct interfacial reaction between the molten aluminum (Al) and the D reinforcement, forming Al carbide at the Al–D interface. Moreover, Al composites processed under optimal energy density exhibit an enhanced Young's modulus. It is highlighted that optimizing LPBF processing parameters is crucial to achieve superior material properties in MMCs, while controlled matrix–reinforcement interactions offer the potential for tailored properties
Diamond coatings on femtosecond-laser-textured stainless steel 316 surfaces for enhanced adherence
No full textA challenge for directly coating diamond on metallic substrates is the large residual stress near their interfaces due to the large mismatch in the coefficients of thermal expansion (CTEs) that leads to cracking or delamination of the diamond coatings from the substrates. In this work, femtosecond (fs)-laser texturing was applied to fabricate various periodic microgrids on stainless steel (SS) 316 substrates for enhancing the adherence between the SS 316 substrates and the diamond coatings grown using the laser-assisted combustion flame chemical vapor deposition (CVD). Through adjusting the dimensions of the microgrids with different fs scanning parameters, the diamond coatings with a maximum thickness of 19 μm can be grown with quality factors up to 96 % as analyzed by Raman spectroscopy. The corresponding large diamond crystals with an average grain size of 9 μm can be obtained on SS316 substrates by optimizing the fs-laser texturing process. The enhanced adherence between the SS 316 substrates and diamond coatings can be attributed to the stress relief and the improved mechanical bonding. The growth kinetics of the diamond coatings on fs-laser-textured SS 316 substrates were also revealed through the phase constitutions and morphology characteristics. This work is anticipated to provide a new strategy and guidance for the growth of diamond coatings on metallic materials with strong adherence at the interfaces
