Improved copper–epoxy adhesion by laser micro- and nano-structuring of copper surface for thermal applications

The objective of this work is the enhancement of metal-to-metal bonding to provide high thermal conductivity together with electrical insulation, to be used as heat sinks at room and cryo-genic temperatures. High thermal conductive metal (copper) and epoxy resin (Stycast 2850FT) were used in this study, with the latter also providing the required electrical insulation. The copper surface was irradiated with laser to induce micro- and nano-patterned structures that result in an improvement of the adhesion between the epoxy and the copper. Thus, copper-to-copper bonding strength was characterized by means of mechanical tensile shear tests. The effect of the laser processing on the thermal conductivity properties of the Cu/epoxy/Cu joint at different temperatures, from 10 to 300 K, is also reported. Using adequate laser parameters, it is possible to obtain high bonding strength values limited by cohesive epoxy fracture, together with good thermal conductivity at ambient and cryogenic temperatures. © 2021 by the authors. Licensee MDPI, Basel, Switzerland

The spontaneous escape behavior of silver from graphite-like carbon coatings and its effect on corrosion resistance

Silver-doped graphite-like carbon (Ag-GLC) coatings were prepared on the surface of aluminum alloy and single-crystal silicon by magnetron sputtering under different deposition parameters. The effects of silver target current and deposition temperature, as well as of the addition of CH4 gas flow, on the spontaneous escape behavior of silver from the GLC coatings were investigated. Furthermore, the corrosion resistance of the Ag-GLC coatings were evaluated. The results showed that the spontaneous escape phenomenon of silver could take place at the GLC coating, regardless of preparation condition. These three preparation factors all had an influence on the size, number and distribution of the escaped silver particles. However, in contrast with the silver target current and the addition of CH4 gas flow, only the change in deposition temperature had a significant positive effect on the corrosion resistance of the Ag-GLC coatings. The Ag-GLC coating showed the best corrosion resistance when the deposition temperature was 500 °C, which was due to the fact that increasing the deposition temperature effectively reduced the number of silver particles escaping from the Ag-GLC coating

Large enhancement of thermal conductance at ambient and cryogenic temperatures by laser remelting of plasma-sprayed Al2O3 coatings on Cu

Joints of high thermal contact conductance and electrical insulation have been obtained by coating copper supports with thin alumina (Al2O3) layers (of 140–150 µm thickness). This has been achieved by a combination of plasma spraying process and the subsequent coating remelting by a near-Infrared (n-IR) laser. With a proper optimization of the laser processing conditions, it is possible to transform the metastable ¿-Al2O3 phase of the as-sprayed coatings to stable a-Al2O3, and to achieve denser alumina coatings. This results in a large enhancement of the thermal conductance of the joints, enabling their application as heat sinks at cryogenic and ambient temperatures. The process proposed in this work is scalable for the formation of alumina coatings on large metallic pieces of complex geometries. © 202

Properties and antibacterial activity of MnFe2O4 nanoparticles obtained by pulsed laser ablation in liquid

In this study, MnFe2O4 nanoparticles (NPs) were fabricated via pulsed laser ablation in liquid. Chemical and structural composition, microstructure, magnetic and antibacterial properties were characterized. Spinel was found as the main crystalline phase, while Fe2O3 and Mn2O3 were observed as the major secondary phases, all identified by X-ray diffractometry (XRD). Observation by Transmission Electron Microscopy (TEM) indicated that most of the nanoparticles were spherical in shape and found in agglomerates, most likely because of their magnetic nature. Moreover, Fast Fourier Transform of selective area electron diffraction patterns pointed at the existence of crystalline particles. The coercive field (Hc) and saturation magnetization (Ms) values determined for these NPs were found to increase with decreasing temperature. Their antibacterial properties were evaluated using the viable bacteria counting technique (colony) for MnFe2O4 concentrations of 100 and 300 μg/mL with Bacillus subtilis, Salmonella typhimurium, Pseudomonas aeruginosa, Klebsiella pneumoniae and Escherichia coli strains

Laser floating zone growth: Overview, singular materials, broad applications, and future perspectives

The Laser Floating Zone (LFZ) technique, also known as Laser-Heated Pedestal Growth (LHPG), has been developed throughout the last several decades as a simple, fast, and crucible-free method for growing high-crystalline-quality materials, particularly when compared to the more conventional Verneuil, Bridgman-Stockbarger, and Czochralski methods. Multiple worldwide efforts have, over the years, enabled the growth of highly oriented polycrystalline and single-crystal high-melting materials. This work attempted to critically review the most representative advancements in LFZ apparatus and experimental parameters that enable the growth of high-quality polycrystalline materials and single crystals, along with the most commonly produced materials and their relevant physical properties. Emphasis will be given to materials for photonics and optics, as well as for electrical applications, particularly superconducting and thermoelectric materials, and to the growth of metastable phases. Concomitantly, an analysis was carried out on how LFZ may contribute to further understanding equilibrium vs. non-equilibrium phase selectivity, as well as its potential to achieve or contribute to future developments in the growth of crystals for emerging applications

Large enhancement of thermal conductance at ambient and cryogenic temperatures by laser remelting of plasma-sprayed Al2O3 coatings on Cu

Joints of high thermal contact conductance and electrical insulation have been obtained by coating copper supports with thin alumina (Al2O3) layers (of 140–150 μm thickness). This has been achieved by a combination of plasma spraying process and the subsequent coating remelting by a near-Infrared (n-IR) laser. With a proper optimization of the laser processing conditions, it is possible to transform the metastable γ-Al2O3 phase of the assprayed coatings to stable α-Al2O3, and to achieve denser alumina coatings. This results in a large enhancement of the thermal conductance of the joints, enabling their application as heat sinks at cryogenic and ambient temperatures. The process proposed in this work is scalable for the formation of alumina coatings on large metallic pieces of complex geometries.

Ultra-Short Pulse Laser Cleaning of Contaminated Pleistocene Bone: A Comprehensive Study on the Influence of Pulse Duration and Wavelength

The impact of wavelength and pulse duration in laser cleaning of hard blackish contaminants crust from archaeologically significant Pleistocene bone is investigated in this research. The objective is to determine the practical cleaning procedures and identify adequate laser parameters for cleaning archaeological bone from Sima de los Huesos (Spain) based on conservation and restoration perspectives. Bone surface cleaning was performed utilizing two Q-switched Nd:YAG lasers: subnanosecond pulsed lasers with emission wavelengths at 355 nm and 1064 nm, respectively, and a Yb:KGW femtosecond pulsed laser with an emission wavelength in the third harmonic at 343 nm. In all experiments, the laser beam scanning mode was applied to measure cleaning efficiency in removing contaminants and degradation products while assessing the underlying substrate surface damage. Several properties, including wavelength-dependent absorption, pulse repetition rate, and thermal properties of the material, are analyzed when evaluating the ability of these lasers to boost the cleaning efficiency of the deteriorated bone surface. Bone surface morphology and composition were studied and compared before and after laser irradiation, using Optical Microscopy, Scanning Electron Microscopy with Energy Dispersive X-ray Spectrometry (SEM-EDS), Fourier Transform Infrared Spectroscopy (FTIR), and X-ray Photoelectron Spectroscopy (XPS) characterization methods. The results indicate that 238-femtosecond UV laser irradiation with 2.37 TWcm−2 is significantly safer and more efficient toward surface contaminant desorption than sub-nanosecond laser irradiation. The results herein presented suggest that these types of fs lasers may be considered for realistic laser conservation of valuable historic and archaeological museum artifactsEuropean Commission - H2020-MSCA-ITN-EJD ED-ARCHMAT PROJECT - GA 76631

Laser-induced scanning transfer deposition of silver electrodes on glass surfaces: A green and scalable technology

A pulsed laser ablation backwriting technique with high repetitive rates is implemented for the fabrication of silver coatings on glass surfaces. This method enables geometrical constraint-free deposition of metallic coatings. These exhibit sufficiently low electrical resistance to be used as electrodes in dielectric barrier discharge (DBD) plasma elements. Ambient air deposition of metallic silver electrodes on standard glass slides is explored using a sub-ns UV laser source, combined with hybrid beam scanning methods. The green nature of the overall deposition process includes a preliminary irradiation scan to homogenise the target surface before the subsequent backwriting step. Metal transfer is achieved by combining two phenomena within a simple beam scanning process: LIRT (laser-induced reverse transfer) of silver from the target to the glass, with a partial and secondary LIFT (Laser-Induced Forward Transfer) of silver from the glass to the target. Appropriate selection of pulse energy and pulse repetition rates, beam scanning velocities and target motion enable the growth of sufficiently thick Ag deposits on glass with the required low electrical resistivity and nearly 2D constraint-free geometry. This method avoids the use of vacuum and liquids, resulting in a cheap, facile and green methodology for the deposition of silver electrodes onto transparent substrate surfaces

Ultrashort pulsed Femtosecond UV laser for selective cleaning of significant Cretaceous flints

This work reports on studies aimed to evaluate the utilization of ultrashort 238 fs (fs) pulsed UV laser emission at 343 nm for eliminating colored crusts and surface deposits on significant Cretaceous flint surfaces, in an attempt to safeguard its aesthetic appearance and archaeological value. The results indicate that fs UV lasers may be an ideal, non-contact tool for selective surface cleaning of sensitive archaeological artefacts, since they enable contaminant desorption while avoiding photothermal damage.European Commission H2020-MSCA-ITN-EJD ED-ARCHMAT - GA 76631

Desarrollo de procesos de limpieza de materiales metálicos con tecnologías láser. Aplicación en patrimonio.

La limpieza láser es una técnica moderna que puede utilizarse para eliminar los productos de corrosión y la contaminación en objetos metálicos. Sin embargo, para implantar esta técnica como un procedimiento estándar de limpieza en conservación del patrimonio, todavía es necesario explorar y definir metodologías concretas. En este trabajo, se han desarrollado experimentos de limpieza láser modificando y optimizando parámetros que incluyen la potencia, la frecuencia de repetición de pulsos, el interlineado láser y la velocidad de barrido, empleando láseres pulsados que emiten con diferentes longitudes de onda (infrarrojo y ultravioleta) y diferentes anchuras de pulso (50 ns, 800 ps y 300 ps). También se han definido protocolos de limpieza combinando el uso de varios láseres y en diferentes atmósferas, habiendo realizado tratamientos en aire, con la muestra inmersa en agua o con una capa de hidrocarburos. Utilizando técnicas de caracterización que incluyen difracción de rayos X, microscopía electrónica de barrido (FESEM), espectroscopía Mössbauer y microscopía confocal, se ha determinado la composición química y la microestructura resultante y asociada a cada tipo de tratamiento láser realizado. Se ha prestado una especial atención a las transformaciones de los compuestos de Fe inducidas por irradiación láser