1,720,993 research outputs found
Laser fabrication of anti-icing surfaces: A review
Full text linkIn numerous fields such as aerospace, the environment, and energy supply, ice generation and accretion represent a severe issue. For this reason, numerous methods have been developed for ice formation to be delayed and/or to inhibit ice adhesion to the substrates. Among them, laser micro/nanostructuring of surfaces aiming to obtain superhydrophobic behavior has been taken as a starting point for engineering substrates with anti-icing properties. In this review article, the key concept of surface wettability and its relationship with anti-icing is discussed. Furthermore, a comprehensive overview of the laser strategies to obtain superhydrophobic surfaces with anti-icing behavior is provided, from direct laser writing (DLW) to laser-induced periodic surface structuring (LIPSS), and direct laser interference patterning (DLIP). Micro-/nano-texturing of several materials is reviewed, from aluminum alloys to polymeric substrates
Sorting of particles using inertial focusing and laminar vortex technology: A review
Full text linkThe capability of isolating and sorting specific types of cells is crucial in life science, particularly for the early diagnosis of lethal diseases and monitoring of medical treatments. Among all the micro-fluidics techniques for cell sorting, inertial focusing combined with the laminar vortex technology is a powerful method to isolate cells from flowing samples in an efficient manner. This label-free method does not require any external force to be applied, and allows high throughput and continuous sample separation, thus offering a high filtration efficiency over a wide range of particle sizes. Although rather recent, this technology and its applications are rapidly growing, thanks to the development of new chip designs, the employment of new materials and microfabrication technologies. In this review, a comprehensive overview is provided on the most relevant works which employ inertial focusing and laminar vortex technology to sort particles. After briefly summarizing the other cells sorting techniques, highlighting their limitations, the physical mechanisms involved in particle trapping and sorting are described. Then, the materials and microfabrication methods used to implement this technology on miniaturized devices are illustrated. The most relevant evolution steps in the chips design are discussed, and their performances critically analyzed to suggest future developments of this technology
Single-pass direct laser cutting of quartz by IR femtosecond pulses
No full textIn this work, we report on a single-pass method for cutting 250-μm thick Z-cut quartz plates using 200 fs laser pulses at the wavelength of 1030 nm. In particular, we delve into the influence of the process parameters, i.e. laser repetition rate, scan speed and pulse energy, on the generation of a controlled stress-induced fracture which ultimately leads to the final cut. Processing above a certain threshold pulse energy caused significant damage, resulting in poor quality cuts. Whereas, a correct combination of these parameters led to a flat and almost defect-free cut edges, in a single pass
Bonding of PMMA to silicon by femtosecond laser pulses
Full text linkMany devices and objects, from microelectronics to microfluidics, consist of parts made from dissimilar materials, such as different polymers, metals or semiconductors. Techniques for joining such hybrid micro-devices, generally, are based on gluing or thermal processes, which all present some drawbacks. For example, these methods are unable to control the size and shape of the bonded area, and present risks of deterioration and contamination of the substrates. Ultrashort laser bonding is a non-contact and flexible technique to precisely join similar and dissimilar materials, used both for joining polymers, and polymers to metallic substrates, but not yet for joining polymers to silicon. We report on direct transmission femtosecond laser bonding of poly(methyl methacrylate) (PMMA) and silicon. The laser process was performed by focusing ultrashort laser pulses at high repetition rate at the interface between the two materials through the PMMA upper layer. The PMMA-Si bond strength was evaluated as a function of different laser processing parameters. A simple, analytical, model was set up and used to determine the temperature of the PMMA during the bonding process. As a proof of concept, the femtosecond-laser bonding of a simple hybrid PMMA-Si microfluidic device has been successfully demonstrated through dynamic leakage tests
Improving the laser texture strategy to get superhydrophobic aluminum alloy surfaces
No full textChanging the wetting properties of surfaces is attracting great interest in many fields, in particular to achieve a surface with a superhydrophobic behavior. Laser machining is an emerg-ing technique to functionalize materials with high precision and flexibility without any chemical treatment. However, when it is necessary to treat large area surfaces laser-based methods are still too slow to be exploited in industrial productions. In this work, we show that by improving the laser texture strategy it is possible to reduce the laser processing time to produce superhydrophobic aluminum alloy surfaces. Three different surface texture geometries were micromachined; namely, square, circular and triangular lattice grooves. We found that if the spacing between the grooves is narrow, i.e., when the percentage of the textured surface is high, the volume of air trapped inside the micromachined structures plays an important role in the wetting behavior. Meanwhile, when the groove spacing approaches the droplet dimensions, the texture geometry has a preponderant influence. Based on these findings an appropriate choice of the laser texture strategy allowed the fabrication of superhydrophobic aluminum alloy surfaces with a 10% reduction of processing time
Investigation of the micro-milling process of steel with THz bursts of ultrashort laser pulses
No full textBurst mode (BM) processing with femtosecond laser pulses is emerging as a versatile tool for manufacturing micro-components on different materials, thanks to its ability to reduce the thermal load, which ensures highly precise and accurate miniaturization. However, a systematic investigation of the influence of the experimental parameters introduced by such irradiation mode, i.e., the number of pulses within the burst, their polarization and the intra-burst frequency, on the ablation process has not been reported, yet. In this work, we exploited a statistical approach based on the Design of Experiment (DoE) to study the micro-milling process of steel with bursts. Two prediction models were defined, describing the relationship between the working parameters, i.e., average power, number of overscans, laser repetition rate, scan speed and number of pulses within the bursts, and the response variables, i.e., ablated depth and surface roughness, revealing burst mode as a very promising solution to improve the surface finishing of ultrashort laser pulses micromilled components
Ultrashort laser welding of PMMA to silicon
No full textUtilization of parts made by combining dissimilar materials, such as different polymers, metals, or semiconductor to polymers, are nowadays highly demanded for the fabrication of electronic, electromechanical, medical micro-devices, and analytical systems (e.g., lab-on-chip). Techniques for joining such hybrid micro-devices, generally based on gluing or thermal processes, remain a challenging task presenting some drawbacks, such as deterioration and contamination of the substrates. Ultrashort laser welding is a non-contact and flexible technique to precisely weld similar and dissimilar materials. In this case, the only constrain is that the upper substrate is transparent to the laser wavelength. This technique has been demonstrated both for welding polymers and polymers to metallic substrates, but never for joining polymers to silicon. In this work, we report on direct femtosecond laser welding of Poly(methyl methacrylate) (PMMA) and silicon. The laser welding was performed in ambient air by focusing ultrashort laser pulses at high repetition rate at the interface between the two, being PMMA transparent to the laser wavelength. A mechanical homogenous pressure was applied on the sandwiched substrates during all the laser process. The Si-PMMA weld strength was evaluated as a function of the laser and processing parameters, e.g., repetition rate, scan speed, and the overlap between adjacent scan lines
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
- …
