3-D aluminum nanostructure with microhole array synthesized by femtosecond laser radiation for enhanced light extinction

This article presents 3-D aluminum micro-nanostructures for enhanced light absorption. Periodic microhole arrays were created by firing a train of femtosecond laser pulses at megahertz pulse frequency onto the surface of an aluminum target at ambient conditions. The laser trains ablated the target surface and created microholes leading to the generation of deposited nanostructures inside and around the microholes. These micro-nanostructures showed enhanced light absorption, which is attributed to surface plasmonics induced by the generation of both nano- and microstructures. These micro-nanostructures may be promising for solar cell applications.     

Study of nanostructure growth with nanoscale apex induced by femtosecond laser irradiation at megahertz repetition rate

Leaf-like nanostructures with nanoscale apex are induced on dielectric target surfaces by high-repetition-rate femtosecond laser irradiation in ambient conditions. We have recently developed this unique technique to grow leaf-like nanostructures with such interesting geometry without the use of any catalyst. It was found to be possible only in the presence of background nitrogen gas flow. In this synthesis method, the target serves as the source for building material as well as the substrate upon which these nanostructures can grow. In our investigation, it was found that there are three possible kinds of nanotips that can grow on target surfaces. In this report, we have presented the study of the growth mechanisms of such leaf-like nanostructures under various conditions such as different laser pulse widths, pulse repetition rates, dwell times, and laser polarizations. We observed a clear transformation in the kind of nanotips that grew for the given laser conditions.     

High-temperature silicon carbide material with wicking and evaporative cooling functionalities fabricated by femtosecond laser surface nano/microstructuring

A multifunctional silicon carbide (6H–SiC) material with efficient wicking and evaporative cooling performances in a temperature range of 23–180 °C is created through hierarchical surface nano/microstructuring by a femtosecond laser. The elaborated hierarchical surface structure is an array of nanotextured microgrooves that includes structural features in a range between about 15 nm and 140 μm, integrating benefits from micro- and nanoscale physics of capillarity and thermodynamics. The spatiotemporal dynamics of both water spreading and temperature field obtained by optical and infrared imaging show the excellent wicking and evaporative cooling functionalities of the created material. The range of applications of the developed multifunctional 6H–SiC material includes the technologies for enhancing power generation efficiency, waste heat recovery, and cooling high-heat-flux Si- and SiC-based electronic devices. The application of the created material in cooling technologies for power generation can result in substantial fuel savings and global reduction in greenhouse gas emissions.     

Two-stage model of nanocones formation on a surface of elementary semiconductors by laser radiation

ABSTRACT: In this work we study mechanism of nanocone formation on a surface of elementary semiconductors by Nd:YAG laser radiation. Our previous investigations of SiGe and CdZnTe solid solutions have shown that nanocone formation mechanism is characterised by two stages. The first stage is characterized by formation of heterostructure. For example, Ge/Si heterostructure from SiGe solid solutions, and the second stage is characterized by formation of nanocones by mechanical plastic deformation of the compressed Ge layer on Si due to mismatch of Si and Ge crystalline lattice. The mechanism of nanocone formation for elementary semiconductors is not clear until now. Therefore, the main goal of our investigations is to study the stages of nanocone formation in elementary semiconductors. A new mechanism of p-n junction formation by laser radiation in the elementary semiconductor as a first stage of nanocones formation is proposed. We explain this effect by following way: p-n junction is formed by generation and redistribution of intrinsic point defects in temperature gradient field - the Thermogradient effect, which is caused by strongly absorbed laser radiation. According to the Thermogradient effect, interstitial atoms drift towards the irradiated surface, but vacancies drift to the opposite direction - in the bulk of semiconductor. Since interstitials in Ge crystal are of n-type and vacancies are known to be of p-type, a n-p junction is formed. The mechanism is confirmed by appearance of diode-like current-voltage characteristics after i-Ge irradiation crystal by laser radiation. In Si mechanism is confirmed by conductivity type inversion and increase microhardness of Si crystal. The second stage of nanocone formation is laser heating up of top layer enriched by interstitial atoms with its further plastic deformation due to compressive stress caused by interstitials in the top layer and vacancies in the buried layer.     

Insight into dynamics of polyelectrolyte chains in salt-free solutions by laser light scattering and analytical ultracentrifugation

We have investigated the dynamics of xanthan aqueous solutions with and without added salt (NaCl) by using laser light scattering (LLS) and analytical ultracentrifugation (AUC) via sedimentation velocity (SV). The fast and slow modes are observed in salt-free and low-salt xanthan solutions by dynamic light scattering (DLS). The scattering ratio (KC/R_s(q)) and apparent diffusion coefficient (D_s,app(q)) of the slow mode is linearly related to scattering vector (q²), indicating that it is related to the diffusion of scattering objects. The intensity contribution (α_s) of the slow mode is independent of scattering angles, indicating that the slow mode is not related to some scattering objects larger than the LLS observation length. However, the slow mode disappears in SV experiments, indicating that it arises from the temporal aggregates due to long range electrostatic interactions between chains, which can be destroyed in centrifugal field. The diffusion coefficient measured by SV is close to that of the fast mode in DLS measurements, indicating that it is the coupling diffusion of macroions and counterions. The present studies also demonstrate that the chain stiffness does not change the characteristics of the dynamics of polyelectrolyte in solutions.     

Tunability of form birefringence induced by femtosecond laser irradiation in anion‐doped silica glass

Form birefringence originating from self‐assembly of the bulk nanograting structures in silica glass with various anion dopants (OH, Cl and F) was induced by the femtosecond laser pulses. Despite the almost similar nanostructure, the photo‐induced birefringence can be changed by the anion dopants in glass. Larger birefringence can be induced in silica glass doped with higher Cl ion concentration. Even if F‐doped silica glass indicates lower thermal stability, its lifetime could be evaluated to be at least several billion years.     

Chromium powder as a reference material for the quality control of particle-size measurement by laser diffraction

Chromium is an important alloying element for aluminium melts. During aluminium cast house practice, chromium is mainly added to melts of aluminium in the holding furnace as tablets or minitablets (compressed compacts of chromium and aluminium powders). Particle-size analyses of chromium powder used as raw material can routinely be carried out by laser diffraction to assure correct packing. Factors affecting the laser diffraction analysis were studied by means of designed experiments in order to improve and control the quality of such particle-size measurements. Moreover, a laboratory reference material based on chromium powder was produced to assure the quality control of particle-size measurements. The material was carefully handled (collection, pre-treatment and preservation) and its homogeneity and term stability were verified. Laser diffraction analyses were validated against sieve-type measurements for the same material.     

Micro-welding of sapphire and metal by femtosecond laser

A direct joining of sapphire and Fe–36Ni alloy was successfully realized via femtosecond laser micro-welding for the first time. A sound joint without any voids or microcracks was obtained with a narrow interface width less than 1 μm. There was no obvious element diffusion or metallurgical reactions at the interface. Sapphire and Fe–36Ni alloy were found chemically bonded and mechanically interlocked evidenced by jagged feature at the interface due to “cold” machining of femtosecond laser ablation. The highly localized femtosecond laser irradiation and smaller heat-affected zone contributed to the shear strength of the joint as high as 108.35 MPa. A higher laser scanning speed corresponded with less jagged feature and thermal stress due to the reduced thermal deposition at the interface. Proper micro-welding parameters were obtained for sapphire/Fe–36Ni alloy, and was verified in the direct joining of sapphire/steel and sapphire/silicon. It appears the femtosecond laser micro-welding technique is promising for direct joining of materials with large physical property disparities, and beneficial for manufacturing of optomechanical components at high precision, efficiency and performance.     

Three-dimensional complex construct fabrication of illite by digital light processing-based additive manufacturing technology

Illite is a group of clay minerals that are expected to be widely used in catalyst fabrication, radioactive element adsorption, and so forth, due to its excellent adsorption properties. However, the shape control limitation of the illite product should be overcome to maximize its utilization and properties. We herein propose additive manufacturing (AM) as one of the best solutions to solve this structural drawback. Digital light processing (DLP) technology with the film-type of the material supplying system was adapted instead of the general vat-type DLP system to increase illite printability. The photo-curability and printability of illite-contained photocurable suspension were optimized. The color effect due to different ferric oxide content in yellow- and white-illite which influence the photopolymerization process also adjusted thoroughly. White illite showed better photo-curability and could be increased solid loading than yellow illite. The defect-free illite products with three-dimensional complex structures, which cannot be produced by typical ceramic processes, were obtained by DLP technology for both yellow- and white-illite after sintering at 1100°C. The overcoming of shape control limitation of illites by ceramic AM proved in this study has excellent potential for expanding illite utilities in various applications.     

Formation mechanisms of nano and microcones by laser radiation on surfaces of Si,Ge, and SiGe crystals

In this work we study the mechanisms of laser radiation interaction with elementary semiconductors such as Si and Ge and their solid solution SiGe. As a result of this investigation, the mechanisms of nanocones and microcones formation on a surface of semiconductor were proposed. We have shown the possibility to control the size and the shape of cones both by the laser. The main reason for the formation of nanocones is the mechanical compressive stresses due to the atoms’ redistribution caused by the gradient of temperature induced by strongly absorbed laser radiation. According to our investigation, the nanocone formation mechanism in semiconductors is characterized by two stages. The first stage is characterized by formation of a p-n junction for elementary semiconductors or of a Ge/Si heterojunction for SiGe solid solution. The generation and redistribution of intrinsic point defects in elementary semiconductors and Ge atoms concentration on the irradiated surface of SiGe solid solution in temperature gradient field take place at this stage due to the thermogradient effect which is caused by strongly absorbed laser radiation. The second stage is characterized by formation of nanocones due to mechanical plastic deformation of the compressed Ge layer on Si. Moreover, a new 1D-graded band gap structure in elementary semiconductors due to quantum confinement effect was formed. For the formation of microcones Ni/Si structure was used. The mechanism of the formation of microcones is characterized by two stages as well. The first stage is the melting of Ni film after irradiation by laser beam and formation of Ni islands due to surface tension force. The second step is the melting of Ni and subsequent manifestations of Marangoni effect with the growth of microcones.     

Cylindrical-electrode-assisted solution blowing for nanofiber spinning

In this article, a novel process called cylindrical-electrode-assisted solution blowing spinning (CSBS) for producing excellent quality nanofibers with simultaneous electrostatic force and air stretching is reported. The originality of this work is in a new apparatus. With a cylindrical electrode, the solution jets were noncontact charged because of electrostatic induction; this is different from traditional solution-blowing spinning (SBS). Poly(ethylene oxide) nanofibers were fabricated by the CSBS technique for the first time. The scanning electron microscopy results prove that the nanofiber mats produced by CSBS and formed by individual cylindrical-shaped fibers presented a more regular morphology than SBS ones. Compared with that of SBS fibers, the CSBS fiber diameter standard deviation decreased by 21%, and the mean diameter decreased by 6.17%. Their thinner and more uniform fibers may make CSBS fiber webs a better candidate for filtration and other uses compared with SBS ones. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47087.     

Removal of the herbicide Bentazon from contaminated water in the presence of synthesized nanocrystalline TiO2 powders under irradiation of UV-C light

A solution-based processing method has been used to synthesize nanocrystalline TiO₂ powders by controlling the hydrolysis of TiCl₄ in an aqueous solution in both anatase and rutile phases. The primary particle sizes of the powders were in the range of 5-15 nm. To determine the crystal phase composition and size of the prepared photocatalysts, X-ray diffraction (XRD) measurements were used. We also studied the photocatalytic removal of the herbicide, Bentazon, from contaminated water in the presence of synthesized nanocrystalline TiO₂ powders under UV light illumination (30 W). The removal efficiency of Bentazon was 16% when the photolysis was carried out in the absence of TiO₂ and it was negligible in the absence of UV light. We have studied the influence of the basic operational parameters such as the different kinds of TiO₂, amount of TiO₂, irradiation time and initial concentration of Bentazon on the photocatalytic removal efficiency of Bentazon. Our results indicated that 99% removal of the herbicide from the solution containing 15 ppm of Bentazon after selecting desired operational parameters could be achieved in a relatively short time, about 90 min. A kinetic model was successfully established for the prediction of removal of Bentazon by the UV/TiO₂ system with any concentration of the herbicide. In this work, we also compared the photocatalytic activity between the commercial TiO₂ and synthesized nanocrystalline TiO₂ powders. The photocatalytic activities of different photocatalysts were tested using the herbicide solution.     

Microstructure and wear resistance of in-situ synthesized Ti(C,N) ceramic reinforced Fe-based coating by laser cladding

In order to enhance the wear resistance of Fe-based cladding layer, TiN, Ti and graphite were added into Fe313 powder and in-situ formation of Ti(C, N) ceramic reinforcement phase was carried out by laser cladding. Firstly, thermodynamic calculations were used to determine the feasibility and favorability of a chemical reaction. Then, the reaction mechanism was investigated by adding five groups of different contents and carrying out EDS and phase analysis. We report that large TiN particles do not completely decompose and in-situ synthesized TiC phase forms around large TiN particles. However, small TiN particles are completely decomposed and directly formed the Ti(C, N) phase. Finally, through the friction and wear tests, it has been observed that the friction coefficient of a sample, with three powders added, was 0.559 times smaller than the substrate and 0.725 times smaller than the initial powder, and the wear volume of the same sample was 0.365 times smaller than the substrate and 0.799 times smaller than the initial powder. Therefore, it can be concluded that the in-situ synthesis of Ti(C, N) ceramic reinforced Fe-based coatings by laser cladding greatly improves the wear resistance of the Fe313 layer.     

Characterization of disbonds in a nuclear radiation protection structure using laser ultrasonics

Characterization of disbonds in a nuclear radiation protection structure (NRPS) has been investigated by laser ultrasonics. Characteristics of laser ultrasonic waves in an NRPS have been researched by simulations and experiments. The signal-to-noise ratio of laser ultrasonic signals in the adhesive structure can be improved by wavelet threshold de-noising (WTDN) and band-pass filtering. Original laser ultrasonic signals were processed by WTDN to implement C-scans which have high contrast to noise ratio. Laser ultrasonic C-scan results can accurately characterize the disbonds, which are in reasonable agreement with the immersion ultrasonic detection result. Therefore, laser ultrasonics has potential for non-destructive evaluation of the bonding quality of NRPSs.     

In situ fabrication of highly-dense Al2O3/YAG nanoeutectic composite ceramics by a modified laser surface processing

Alumina-matrix eutectic in situ composite ceramics present excellent high-temperature mechanical properties, which have been considered as promising next-generation ultra-high temperature structural materials. A modified laser surface processing is developed to in situ fabricate highly-dense Al₂O₃/YAG bulk nanoeutectic ceramics with large size and homogeneous three-dimensional network of nanoeutectic microstructure by introducing two-side remelting and high-temperature preheating. The crack and porosity are avoided, and the eutectic structure achieves a good continuous growth between two solidified layers. The eutectic phases show sharp interface bonding with a defined orientation relationship. The dislocations and crack deflection at high-density phase interfaces importantly contribute to the enhanced fracture toughness.     

Nitride phosphor-in-glass films enabling high-performance white light in transmissive and reflective laser lighting

Phosphor-converted laser lighting has become a credible candidate in next-generation high-brightness white lighting, and the configuration types of phosphor converters have a great influence on the opto-thermal performances of laser lighting. In this work, we proposed nitride phosphor-in-glass films (PIGFs) for high-brightness laser lighting and investigated the opto-thermal performances of PIGFs in transmissive (T) and reflective (R) modes. The Y-PIGFs were prepared by low-temperature sintering a mixture of yellow-emitting La₃Si₆N₁₁:Ce³⁺ (LSN) phosphor and borosilicate glass, and the Y/R-PIGFs were achieved by incorporating red-emitting CaAlSiN₃:Eu²⁺ (CASN) phosphor into the Y-PIGFs. The PIGFs display higher thermal stability and luminescence intensity than the raw phosphors. By tailoring the thickness of Y-PIGFs, the Y-PIGF with a film thickness of 75 μm achieves the luminous efficacy of 199.4 lm/W and 91.5 lm/W in the T mode and R mode, respectively, and the PIGF realizes the highest luminous efficacy of 207.8 lm/W by collecting backward light in the T mode. At the CASN/LSN ratio of 0.20, the Y/R-PIGF enables high-quality white light with a color rendering index (CRI) higher than 89. Furthermore, under 4.82 W laser excitation, the central temperatures of Y-PIGF in the T-mode and R-mode are only 98 °C and 67.4 °C, respectively. The results indicate that the PIGFs enable high-performance white laser lighting with distinct opto-thermal properties by adjusting configuration types.     

Organic-inorganic composites for novel optical transformation induced by high-energy laser ablation

High-energy continuous-wave (CW) laser has been considered as a significant technology in recent decades. Such laser can destroy conventional materials in an extremely short time, necessitating their protection. In this study, zirconium carbide (ZrC) and silicon carbide (SiC) particle-modified short silicon carbide fiber-reinforced phenolic resin matrix composites (SiC/BPF-ZS) with significant anti-laser performance were designed and prepared. Our results showed that the ceramic particles and SiC fibers rapidly oxidized, leading to the formation of a ceramic coating composed of ZrO₂ and SiO₂. Owing to the formation of the ceramic coating, the reflectivity of the composites improved significantly from 15.8% to 73.2% after ablation at 500 W/cm² for 30 s. Additionally, the SiC fibers played an important role in the formation of a high-reflectivity coating during laser ablation. Contrast experiments indicated that SiC fibers lead to better performance than the carbon fibers. The high reflectivity and low mass ablation rate are demonstrated to be the key factors improving the anti-laser ablation performance of the SiC/BPF-ZS composites.     

Recycled polyester nanofiber as a reservoir for essential oil release

The importance of creating sustainable alternatives for products that can be easily recyclable, such as, poly (ethylene terephthalate) (PET), is not new, being textile fibers the product of greatest interest. The objective of this work is to propose a recycling alternative for PET bottles for fiber production as a reservoir of essential oils for aromatherapy applications. The fibers were obtained via coaxial and dual-jet electrospinning techniques. The material used in the impregnation and release of peppermint oil was PET originating from disposable bottles. The release of oil from the electrospun fibers was quantified by UV–vis spectroscopy. For the fibers produced by dual-jet electrospinning the cumulative release of peppermint reached around 70% after 30 days. The sample obtained by coaxial electrospinning had a core-shell structure and the amount of oil released was 33% after 30 days. In this investigation, a less aggressive process was introduced, making the electrospinning of PET a viable technique for essential oil impregnation. Dual-jet as well as coaxial electrospinning showed slower release than values reported in the literature. Thus, a procedure with more favorable working conditions was developed, making the process more feasible and serving as an alternative for recycling PET bottles to produce functional textiles.     

A comparative investigation on microstructure evolution and wear resistance of in situ synthesized NbC,WC, TaC reinforced Mo2FeB2 coatings by laser cladding

To improve the microhardness and wear resistance of Mo₂FeB₂ coatings, composite coatings were prepared by laser cladding using in situ synthesized NbC, WC, and TaC. The influence of different carbides on the morphology, microstructure, microhardness, residual stress, and tribological properties of the composite coatings was investigated. The results showed various microstructural morphologies in different composite coatings. Apparent herringbone structures were observed in most coatings except for the Mo₂FeB₂/TaC composite coating and a eutectic structure was formed in the Mo₂FeB₂/WC composite coating. In addition, the heat-affected zone was typically composed of acicular martensite and lath martensite. The microhardness of the Mo₂FeB₂/WC composite coating increased to 1543.6 HV_0.5 compared with 985.7 HV_0.5 observed for the Mo₂FeB₂ coating. Tensile stress existed in the coating, bonding zone, and heat-affected zone, whereas the substrate exhibited compressive stress. The Mo₂FeB₂/WC composite coating exhibited the lowest tensile stress (298 MPa). The Mo₂FeB₂/WC composite coating containing WC and the W₂C phase had the lowest coefficient of friction (0.38) and wear rate (3.90 × 10^?5 mm³/Nm), indicating its excellent tribological properties. Moreover, the wear mechanism of the Mo₂FeB₂ coating is severe adhesive and abrasive wear. The adhesive wear mechanism was mitigated by the formation of in situ synthesized NbC, WC, and TaC. The wear mechanism of the Mo₂FeB₂/WC composite coating was only a slight abrasive wear.