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Laser chemical machining (LCM) is a method for removing material by thermally induced chemical dissolution of self-passivating metals. However, the process window is limited by disrupted material removal due to gas bubble formation and metallic salts and oxides deposition at higher energy input. Since the temperature increases, and therefore gas bubble growth takes time, it is hypothesized that the temporal modulation of laser power can remove the metal homogeneously, i.e., without disrupted material removal, while achieving a higher removal rate. Based on this, the dynamic process behavior of material removal is investigated for the LCM of titanium in phosphoric acid, using a rectangular modulation of the laser power with varying irradiation durations. As a result, however, high-speed videos show that gas bubbles are consistently generated, regardless of the applied laser power and power modulation, although the quantity of bubbles varies with different parameters. Even with short power durations (10 ms), the material deposition occurs after multiple irradiations. When the duration is longer, the material deposition increases in height along the laser scan direction. For the studied process parameters, a Fourier analysis in the spatial domain further indicates the correlation between the material removal frequencies and the modulation frequencies. In conclusion, the laser power modulation cannot prevent the disturbed material removal at high laser powers. Nevertheless, the material deposition can be utilized to generate periodic surface structures with a depth below and above the initial surface. [ABSTRACT FROM AUTHOR]

Nowadays, structural colors successfully replace pigment‐based ones. Most of the newly proposed solutions rely on plasmonic systems, so speaking nanosized objects, exhibiting strongly size‐dependent optical properties. As a consequence, the fabrication requires high‐precision and time‐consuming technologies. A concept dealing with sub‐micronic surface features, easily reproducible on a large scale is proposed. The designed metasurface consists of randomly distributed holes serving both as cavity resonators and scatterers. The proposed solution grants an efficient control of the spatial distribution of diffuse light and offers a large palette of vibrant colors. The interferometric model and a two‐layer angular spectrum method provide a solid description of the physical origin of the phenomenon, with a high degree of agreement between simulations and experimental data. [ABSTRACT FROM AUTHOR]

Laser chemical machining (LCM) is a method of laser processing based on gentle material removal by means of thermal induced chemical dissolution. Since LCM depends predominantly on the surface temperature of the workpiece, the process window is restricted by the appearance of gas bubbles at higher laser powers and their associated shielding effect. In order to extend the process understanding, the influence of the laser power modulation on the removal behavior is investigated in the present work. The experiments were conducted on titanium grade 1 and with phosphoric acid. Based on the response time in experiments with a single step function of the laser power, a spatial frequency threshold was determined above which a constant removal depth could be expected. Afterward, the laser power was modulated rectangularly in time, resulting in combination with the process velocity in different spatial modulation frequencies varying from 1 to 20 mm−1. The investigations showed that the removal cavity exhibited sinusoidal oscillation in depth along the machining direction with a spatial frequency corresponding to the spatial frequency of the laser power. When the spatial frequency exceeds the determined threshold frequency, the cavity depth is constant. This established the basis for generating complex removal profiles by varying the power in the range below the threshold frequency. [ABSTRACT FROM AUTHOR]

We experimentally demonstrated that dielectrophoretic (DEP) forces of alternating photovoltaic fields generated near the surface of a photorefractive Fe-doped lithium niobate crystal by an optical Bessel beam with concentric ring structure and 532 nm wavelength exert the structuring of pure glycerin layer on the crystal surface and formation of stationary fluid concentric ring pattern. Taking into account this effect, the manipulation and trapping of the Ag nanoparticles suspended in the thin glycerin layer on the crystal surface with Bessel beam-induced photovoltaic field pattern have been studied. The formation of the clusters of Ag nanoparticles is observed. The localization of the Ag particles on the extremes of fluid lattice rings is detected. The trapping process can be described by a two-stage scenario. In the early stage, the stratification of glycerin thin layer under positive DEP force and localization of the fluid in the maxima of the photovoltaic field take place, thus forming the concentric ring fluid channels on the crystal surface. The flow of viscose glycerin in the radial directions also carries along the Ag nanoparticles. In the advanced stage, the repulsive DEP forces lead to the trapping of Ag particles on the crystal surface at the borderlines of fluid lattice rings. The generated photovoltaic space charge fields are long-living and, as a consequence, the formed patterns remain stable for a long time due to the high resistance of the crystal. The photovoltaic tweezers operating in an autonomous regime and allowing the trapping, manipulation and separation of micro-/nanoparticles are promising for photonics, integrated optics, nanoelectronics and biotechnology. [ABSTRACT FROM AUTHOR]

Photosensitive glasses for radiation-induced 3D microstructuring, due to their optical transparency and thermal, mechanical, and chemical resistance, enable the use of new strategies for numerous microscale applications, ranging from optics to biomedical systems. In this context, we investigated the plasma etching of photosensitive glasses after their exposure and compared it to the established wet chemical etching method, which offers new degrees of freedom in microstructuring control and microsystem fabrication. A CF4/H2 etching gas mixture with a constant volumetric flow of 30 sccm and a variable H2 concentration from 0% to 40% was utilized for plasma-based etching, while for wet chemical etching, diluted hydrofluoric acid (1% ≤ cHF ≤ 20%) was used. Therefore, both etching processes are based on a chemical etching attack involving fluorine ions. A key result is the observed reversion of the etch selectivity between the initial glassy and partially crystallized parts that evolve after UV exposure and thermal treatment. The crystallized parts were found to be 27 times more soluble than the unexposed glass parts during wet chemical etching. During the plasma etching process, the glassy components dissolve approximately 2.5 times faster than the partially crystalline components. Unlike wet chemical etching, the surfaces of plasma etched photostructured samples showed cone- and truncated-cone-shaped topographies, which supposedly resulted from self-masking effects during plasma etching, as well as a distinct physical contribution from the plasma etching process. The influences of various water species on the etching behaviors of the homogeneous glass and partially crystallized material are discussed based on FTIR-ATR and in relation to the respective etch rates and SNMS measurements.

Photosensitive glasses for radiation-induced 3D microstructuring, due to their optical transparency and thermal, mechanical, and chemical resistance, enable the use of new strategies for numerous microscale applications, ranging from optics to biomedical systems. In this context, we investigated the plasma etching of photosensitive glasses after their exposure and compared it to the established wet chemical etching method, which offers new degrees of freedom in microstructuring control and microsystem fabrication. A CF4/H2 etching gas mixture with a constant volumetric flow of 30 sccm and a variable H2 concentration from 0% to 40% was utilized for plasma-based etching, while for wet chemical etching, diluted hydrofluoric acid (1% ≤ cHF ≤ 20%) was used. Therefore, both etching processes are based on a chemical etching attack involving fluorine ions. A key result is the observed reversion of the etch selectivity between the initial glassy and partially crystallized parts that evolve after UV exposure and thermal treatment. The crystallized parts were found to be 27 times more soluble than the unexposed glass parts during wet chemical etching. During the plasma etching process, the glassy components dissolve approximately 2.5 times faster than the partially crystalline components. Unlike wet chemical etching, the surfaces of plasma etched photostructured samples showed cone- and truncated-cone-shaped topographies, which supposedly resulted from self-masking effects during plasma etching, as well as a distinct physical contribution from the plasma etching process. The influences of various water species on the etching behaviors of the homogeneous glass and partially crystallized material are discussed based on FTIR-ATR and in relation to the respective etch rates and SNMS measurements. [ABSTRACT FROM AUTHOR]

Algae are a source of many biologically active compounds that can be used in food production to expand the range of functional products. For instance, sodium alginate possesses a complex of scientifically proven biologically active properties. In the food industry, it usually serves as a thickener, stabilizer, gelatio n agent, and water-retaining agent. The biological activity of this polysaccharide and its effect on the technological properties of food systems depend on the molecular weight and particle size uniformity. The present research objective was to study the method of sonochemical microstructuring of sodium alginate to increase its biological activity and efficiency as part of v arious bakery formulations. The research featured alginate gels, yeast suspensions of Saccharomyces cerevisiae, and bakery products. The sonochemical microstructuring of sodium alginate involved a low-frequency ultrasonic treatment at 240, 435, and 630 W/L and 50°C for 20, 25, and 30 min. The effect of the treatment included the following indicators: particle morphology vs. distribution of the hydrodynamic particle diameter in a dispersed medium, antioxidant activity, dynamic viscosity, in vitro bioactivity, and bioavailability against Paramecium caudatum and S. cerevisiae. The quality assessment of bakery products followed State Standard 58233-2018. The process of sonochemical microstructuring depolymerized large particles of sodium alginate into shorter ones: 5670 nm – 30.6%, 502 nm – 53.4%, 56.1 nm – 16%. It increased the antioxidant activity by 7 times and the potential in vitro bioactivity by 3.9%. The microstructured sodium alginate improved the fermentation activity of S. cerevisiae and reduced the yeast biomass by 8%. The resulting bakery products had a greater porosity by 5.9% and antioxidant activity by 3.7 times. The sonochemical microstructuring reduced the particle size of sodium alginate, as well as increased its biological activity. The sonochemically microstructured sodium alginate demonstrated a great potential for baked foods.

Tungsten is an important material for high‐temperature applications due to its high chemical and thermal stability. Its carbide, that is, tungsten carbide, is used in tool manufacturing because of its outstanding hardness and as a catalyst scaffold due to its morphology and large surface area. However, microstructuring, especially high‐resolution 3D microstructuring of both materials, is a complex and challenging process which suffers from slow speeds and requires expensive specialized equipment. Traditional subtractive machining methods, for example, milling, are often not feasible because of the hardness and brittleness of the materials. Commonly, tungsten and tungsten carbide are manufactured by powder metallurgy. However, these methods are very limited in the complexity and resolution of the produced components. Herein, tungsten ion‐containing organic–inorganic photoresins, which are patterned by two‐photon lithography (TPL) at micrometer resolution, are introduced. The printed structures are converted to tungsten or tungsten carbide by thermal debinding and reduction of the precursor or carbothermal reduction reaction, respectively. Using TPL, complex 3D tungsten and tungsten carbide structures are prepared with a resolution down to 2 and 7 μm, respectively. This new pathway of structuring tungsten and its carbide facilitates a broad range of applications from micromachining to metamaterials and catalysis. [ABSTRACT FROM AUTHOR]

The present work focuses on the shrinkage of PMMA films under irradiation and its application to the creation of optical devices. We prepared the free-standing PMMA films in four different thicknesses (13, 21, 32, and 43 μm), and PMMA films of the same thickness, but deposited on a glass substrate. A diffraction grating was chosen as the optical device to show the applicability of the method. The study revealed that at a film thickness of 13–32 μm, the shrinkage of the free-standing film increases proportionally to its thickness, while the film on the substrate does not have a pronounced dependence. Films with the thickness of 43 µm do not follow this trend. It was found that under the same irradiation conditions, the film on the substrate shrinks more compared to the free-standing film. Interference patterns from the created diffraction gratings were shown to present spurious illumination areas. [ABSTRACT FROM AUTHOR]

The integrated perception capable of detecting and monitoring varieties of activities is one of the ultimate purposes of wearable electronics and intelligent robots. Limited by the space occupation, it lacks practical feasibility to stack multiple types of single sensors on each other. Herein, a high-sensitivity dual-function capacitive sensor with proximity sensing and pressure sensing is proposed. The fringing electric field can be confined in the proximity-sensitive area by fibrous loop-patterned electrode, leading to more stolen charges when object approaching and thus a high proximity sensitivity. The high-permittivity doped structured dielectric layer reduces the compressive stiffness and enhances the rate of compression-caused increase in the equivalent relative permittivity of the dielectric layer, resulting in a larger increase in capacitance and thus a high pressure sensitivity. The electrodes and dielectric layer together compose the capacitor and act as the sensor without taking up additional space. The decoupling of proximity-sensing and pressure-sensing modes can be achieved by decrease or increase in capacitance. Combined with array distribution and sequential scanning, the sensors can be used for detection of motion trajectory, contour recognition, and pressure distribution. [ABSTRACT FROM AUTHOR]

Microfluidic systems have become part of our everyday life, with surface microfluidics occupying its niche in instant diagnostics and point-of-care testing. Implementing surface microfluidics on a large scale appears to be impossible without developing or upgrading manufacturing technologies. Our paper proposes a CO2-laser microtechnology of precise fused silica surface processing. Key microfluidic elements–microchannels, input and deposition reservoirs have been designed, fabricated and tested with picoliter volumes of fluids. Optical transmittance of the elements remains high enough to observe reactions in a microfluidic system by means of optical methods. The above research and its results would contribute to making laser microtechnologies available to a wide range of experimental and commercial users of microfluidics. [ABSTRACT FROM AUTHOR]

Laser microstructuring has been studied extensively in the last decades due to its versatile, contactless processing and outstanding precision and structure quality on a wide range of materials. A limitation of the approach has been identified in the utilization of high average laser powers, with scanner movement fundamentally limited by laws of inertia. In this work, we apply a nanosecond UV laser working in an intrinsic pulse-on-demand mode, ensuring maximal utilization of the fastest commercially available galvanometric scanners at scanning speeds from 0 to 20 m/s. The effects of high-frequency pulse-on-demand operation were analyzed in terms of processing speeds, ablation efficiency, resulting surface quality, repeatability, and precision of the approach. Additionally, laser pulse duration was varied in single-digit nanosecond pulse durations and applied to high throughput microstructuring. We studied the effects of scanning speed on pulse-on-demand operation, single- and multipass laser percussion drilling performance, surface structuring of sensitive materials, and ablation efficiency for pulse durations in the range of 1–4 ns. We confirmed the pulse-on-demand operation suitability for microstructuring for a range of frequencies from below 1 kHz to 1.0 MHz with 5 ns timing precision and identified the scanners as the limiting factor even at full utilization. The ablation efficiency was improved with longer pulse durations, but structure quality degraded. [ABSTRACT FROM AUTHOR]

The surfaces of animals, plants and abiotic structures are not only important for organismal survival, but they have also inspired countless biomimetic and industrial applications. Additionally, the surfaces of animals and plants exhibit an unprecedented level of diversity, and animals often move on the surface of plants. Replicating these surfaces offers a number of advantages, such as preserving a surface that is likely to degrade over time, controlling for non-structural aspects of surfaces, such as compliance and chemistry, and being able to produce large areas of a small surface. In this paper, we compare three replication techniques among a number of species of plants, a technical surface and a rock. We then use two model parameters (cross-covariance function ratio and relative topography difference) to develop a unique method for quantitatively evaluating the quality of the replication. Finally, we outline future directions that can employ highly accurate surface replications, including ecological and evolutionary studies, biomechanical experiments, industrial applications and improving haptic properties of bioinspired surfaces. The recent advances associated with surface replication and imaging technology have formed a foundation on which to incorporate surface information into biological sciences and to improve industrial and biomimetic applications. This article is part of the theme issue Bioinspired materials and surfaces for green science and technology.

Laser-generated surface patterns provide the means for local mechanical interlocking between the joined materials, tunes the wettability of surfaces that come in contact, and generally are the main factor for bonding strength enhancement, especially between dissimilar materials. This paper presents the influence of different patterning overlays generated with a pulsed laser on the surface of stainless-steel sheets. For all experiments, an overlapping degree of 90% has been chosen between three different patterns, while the engraving speed, pulse frequency and number of passes have varied. The textured surfaces’ morphology was assessed through optical microscopy, and the roughness of the surfaces was correlated with the corresponding experimental parameters. The results have indicated promising insights for joining stainless steel to plastic materials, which is otherwise difficult to assess through usual welding techniques.

The coefficient of friction (COF) is an important parameter for mechanical engineers to consider when designing frictional connections. Previous work has shown that a surface microstructuring of the harder friction partner leads to a significant increase in the COF. However, the impact of the changes in the tribological system on the COF are not known in detail. In this study, the tribological influence factors such as the nominal surface pressure, the material pairing, lubrication, and the surface properties of the counterbody are investigated. Microstructuring is applied by turn-milling of an annular contact surface of cylindrical specimens. A torsional test bench is used to measure the torque depending on the displacement of the two specimens, thus enabling the determination of the COF. All tests with the microstructured specimens result in higher COF than the reference test with unstructured samples. The manufacturing process of the counterbody surface, the nominal surface pressure, and the materials in contact have a significant influence on the COF. While lubrication reduces friction in the case of unstructured specimens, the COF does not change significantly for microstructured samples. This proves that the deformative friction component dominates over the adhesive. Microstructuring the harder friction partner increases the transmittable torque in frictional connections and reduces the sensitivity towards possible contamination with lubricants. [ABSTRACT FROM AUTHOR]

Nanocelluloses are emerging as natural materials with favourable properties for coating industry and can be applied by state-of-the-art spraying technology. While additional functionalities are commonly introduced through chemical modification, the surface microstructuring of nanocellulose coatings with high throughput methods remains unexplored. Here, a femtosecond laser is used for texturing spray-coated coatings made of cellulose nanofibrils (CNF) or cellulose nanocrystals (CNC). For coating thickness of 1.5 to 8 μm, processing limits were determined with maximum ablation energy linearly increasing with coating thickness and minimum ablation energy decreasing or increasing depending on the apparent coating density. Within applicable processing window of pulse rate and power setting, the operational ranges were determined for creating one-dimensional and two-dimensional surface patterns, requiring a higher laser energy for CNC compared to CNF coatings and yielding thinnest possible resolved patterns of 17 μm as determined by the laser spot diameter. The laser ablation under low energy corresponds to an increase in surface roughness and intensifies surface hydrophilicity, while the line patterns are able to pin water droplets with rising water contact angles up to 90°. Present feasibility study opens future possibilities for managing surface properties of nanocellulose coatings in applications where tuning of surface hydrophilicity is required. [Display omitted] [ABSTRACT FROM AUTHOR]

The aim of the present study was to investigate the possibility of encapsulating the plant antioxidant taxifolin in the living cells of the yeast Saccharomyces cerevisiae. Taxifolin is an unstable substance prone to oxidative degradation and actively enters into chemical reactions with a decrease or loss of bioactive properties. To minimize these problems, the use of encapsulation technology has been proposed. The cells of the yeast Saccharomyces cerevisiae have been chosen as a protective material for taxifolin. The encapsulation process was carried out using simple diffusion methods in living Saccharomyces cerevisiae cells in a thermostatically controlled shaker for 24 h. The aim of the study was to evaluate the effect of preliminary microstructuring of taxifolin on the efficiency of its encapsulation in yeast cells. The microstructuring process was carried out using low-frequency ultrasonic cavitation exposure for 7 min with a frequency of 22 ± 1.6 kHz and a power of 600 W/100 mL. The studies confirmed the feasibility of the proposed approach. It was found that microstructuring changes the dispersed composition of taxifolin particles and their morphology in solution and also increases the value of the antioxidant activity. Preliminary microstructuring of taxifolin increases the efficiency of its encapsulation in Saccharomyces cerevisiae yeast cells by 1.42 times compared to the initial form. A positive dependence of the growth of the encapsulation efficiency on the duration of the process was also established. Thus, the conducted studies confirmed the advantage of encapsulation of taxifolin in living cells of the yeast Saccharomyces cerevisiae in microstructured form. [ABSTRACT FROM AUTHOR]

The article is devoted to one of the effective technologies for processing solid transparent materials—thermoplasmonic laser-induced backside wet etching (TP LIBWE). This technology involves aqueous solutions of metal precursors as a working medium. The dependence of the efficiency of sapphire TP LIBWE micromachining on the parameters of laser action is studied with the aqueous solution of the AgNO3 precursor as a working media. The near-optimal range of laser intensities from the point of the etching speed and quality is found. Utilizing the optoacoustic methods, high-speed video, and an optical integrating sphere, the initial stage of the TP LIBWE process is studied in detail. A four-stage model of the TP LIBWE beginning process is proposed, which explains the effects from the beginning of Ag nanoparticle formation in the region of laser exposure to the transition of the TP LIBWE process to a stationary laser microstructuring mode. It is shown that effective microstructuring occurs due to the appearance on the sapphire surface of a thin modified layer in the region of laser action. This thin modified layer is an amorphous Al2O3 with numerous plasmonic Ag nanoparticles inside it and at the sapphire/liquid interface. [ABSTRACT FROM AUTHOR]

By introducing a superconducting gap in Weyl or Dirac semimetals, the superconducting state inherits the nontrivial topology of their electronic structure. As a result, Weyl superconductors are expected to host exotic phenomena, such as nonzero-momentum pairing due to their chiral node structure, or zero-energy Majorana modes at the surface. These are of fundamental interest to improve our understanding of correlated topological systems, and, moreover, practical applications in phase-coherent devices and quantum applications have been proposed. Proximity-induced superconductivity promises to allow these experiments on nonsuperconducting Weyl semimetals. We show a new route to reliably fabricate superconducting microstructures from the nonsuperconducting Weyl semimetal NbAs under ion irradiation. The significant difference in the surface binding energy of Nb and As leads to a natural enrichment of Nb at the surface during ion milling, forming a superconducting surface layer (Tc ~ 3.5 K). Being formed from the target crystal itself, the ideal contact between the superconductor and the bulk may enable an effective gapping of the Weyl nodes in the bulk because of the proximity effect. Simple ion irradiation may thus serve as a powerful tool for the fabrication of topological quantum devices from monoarsenides, even on an industrial scale.

Laser microstructuring has been studied extensively in the last decades due to its versatile, contactless processing and outstanding precision and structure quality on a wide range of materials. A limitation of the approach has been identified in the utilization of high average laser powers, with scanner movement fundamentally limited by laws of inertia. In this work, we apply a nanosecond UV laser working in an intrinsic pulse-on-demand mode, ensuring maximal utilization of the fastest commercially available galvanometric scanners at scanning speeds from 0 to 20 m/s. The effects of high-frequency pulse-on-demand operation were analyzed in terms of processing speeds, ablation efficiency, resulting surface quality, repeatability, and precision of the approach. Additionally, laser pulse duration was varied in single-digit nanosecond pulse durations and applied to high throughput microstructuring. We studied the effects of scanning speed on pulse-on-demand operation, single- and multipass laser percussion drilling performance, surface structuring of sensitive materials, and ablation efficiency for pulse durations in the range of 1–4 ns. We confirmed the pulse-on-demand operation suitability for microstructuring for a range of frequencies from below 1 kHz to 1.0 MHz with 5 ns timing precision and identified the scanners as the limiting factor even at full utilization. The ablation efficiency was improved with longer pulse durations, but structure quality degraded.

Laser-generated surface patterns provide the means for local mechanical interlocking between the joined materials, tunes the wettability of surfaces that come in contact, and generally are the main factor for bonding strength enhancement, especially between dissimilar materials. This paper presents the influence of different patterning overlays generated with a pulsed laser on the surface of stainless-steel sheets. For all experiments, an overlapping degree of 90% has been chosen between three different patterns, while the engraving speed, pulse frequency and number of passes have varied. The textured surfaces' morphology was assessed through optical microscopy, and the roughness of the surfaces was correlated with the corresponding experimental parameters. The results have indicated promising insights for joining stainless steel to plastic materials, which is otherwise difficult to assess through usual welding techniques. [ABSTRACT FROM AUTHOR]

The structuring of mid-IR materials, such as chalcogenide glass (ChG), at the micro and nano scales, is of high interest for the fabrication of photonic devices in general, and for spectroscopy applications in particular. One efficient method for producing regular patterns with a sub-micron to micron length scale is through self-organization processes occurring during femtosecond laser exposure. These processes occur in a broad set of materials, where such self-organized patterns can be found not only on the surface but also within the material volume. This study specifically investigates the case of chalcogenide glass (Ge23Sb7S70) exposed to femtosecond laser pulses, inducing pulse-to-pulse nanostructure formation that is correlated to the glass network structural evolution using Raman spectroscopy as well as morphological and elemental microscopy analysis.

Microstructured antireflective coatings (ARCs) can reduce reflection losses over a wide range of incidence angles when applied to the surface of a high‐efficiency III‐V photovoltaic cell in a concentrator photovoltaic (CPV) system. In this article, we present a microstructured ARC consisting of a monolayer of close‐packed silica microbeads partially submerged within a polydimethylsiloxane (PDMS) cell encapsulant for use within a reference 500× CPV submodule. Comparing a commercialized SiOx encapsulant to this microstructured coating with 25% submerged 1,000 nm‐diameter beads, angle‐dependent external quantum efficiency measurements yield a 2.6% current gain for the microstructured coating. Simulations demonstrate good agreement with measurements, predicting a 2.4% current gain for the same configuration. Extrapolating with our validated model, we estimate a maximum and achievable (within a large manufacturing tolerance) current gain of 3.4% and 2.9 ± 0.4% using 60% submerged and 10%–32% submerged 760 nm‐diameter beads, respectively. [ABSTRACT FROM AUTHOR]

The coefficient of friction (COF) is an important parameter for mechanical engineers to consider when designing frictional connections. Previous work has shown that a surface microstructuring of the harder friction partner leads to a significant increase in the COF. However, the impact of the changes in the tribological system on the COF are not known in detail. In this study, the tribological influence factors such as the nominal surface pressure, the material pairing, lubrication, and the surface properties of the counterbody are investigated. Microstructuring is applied by turn-milling of an annular contact surface of cylindrical specimens. A torsional test bench is used to measure the torque depending on the displacement of the two specimens, thus enabling the determination of the COF. All tests with the microstructured specimens result in higher COF than the reference test with unstructured samples. The manufacturing process of the counterbody surface, the nominal surface pressure, and the materials in contact have a significant influence on the COF. While lubrication reduces friction in the case of unstructured specimens, the COF does not change significantly for microstructured samples. This proves that the deformative friction component dominates over the adhesive. Microstructuring the harder friction partner increases the transmittable torque in frictional connections and reduces the sensitivity towards possible contamination with lubricants.

The aim of the present study was to investigate the possibility of encapsulating the plant antioxidant taxifolin in the living cells of the yeast Saccharomyces cerevisiae. Taxifolin is an unstable substance prone to oxidative degradation and actively enters into chemical reactions with a decrease or loss of bioactive properties. To minimize these problems, the use of encapsulation technology has been proposed. The cells of the yeast Saccharomyces cerevisiae have been chosen as a protective material for taxifolin. The encapsulation process was carried out using simple diffusion methods in living Saccharomyces cerevisiae cells in a thermostatically controlled shaker for 24 h. The aim of the study was to evaluate the effect of preliminary microstructuring of taxifolin on the efficiency of its encapsulation in yeast cells. The microstructuring process was carried out using low-frequency ultrasonic cavitation exposure for 7 min with a frequency of 22 ± 1.6 kHz and a power of 600 W/100 mL. The studies confirmed the feasibility of the proposed approach. It was found that microstructuring changes the dispersed composition of taxifolin particles and their morphology in solution and also increases the value of the antioxidant activity. Preliminary microstructuring of taxifolin increases the efficiency of its encapsulation in Saccharomyces cerevisiae yeast cells by 1.42 times compared to the initial form. A positive dependence of the growth of the encapsulation efficiency on the duration of the process was also established. Thus, the conducted studies confirmed the advantage of encapsulation of taxifolin in living cells of the yeast Saccharomyces cerevisiae in microstructured form.

The field of planar chromatography has seen a resurgence due to interest in novel fabrication techniques for sorbent (stationary phase) layers. These novel sorbents must have high surface areas and achieve separations over short distances. Here, we present the first attempt to fabricate a planar chromatographic platform via laser ablation. Microchannels of 24 µm × 68 µm depth were produced using an Nd:YAG laser on cyclic olefin polymer substrates which act as the stationary phase. These plates were then applied to a proof-of-concept organic dye separation and were able to resolve a binary dye mixture over 11 mm of plate length. Results showed promising potential for laser ablation as a new fabrication technique for planar chromatographic substrates. [ABSTRACT FROM AUTHOR]

A microbial electrolysis cell is set up with the purpose to realize an efficient power‐to‐gas process. Both hydrogen production by electrolysis and biomethanization proceed in the same reactor cell. In particular, the formation of hydrogen bubbles is strongly governed by the surface properties of the used stainless steel electrodes. Here, we introduce surface topography modifications on the micron‐scale to enhance the electrical transport in the cell and support charge conversion into hydrogen. Furthermore, it is analyzed if hydrogen bubble detachment can be supported to form smaller bubbles that can be efficiently converted into methane. A positive influence on the electrical transport is found and explained by a surface‐controlled suppression of bio‐film passivation. [ABSTRACT FROM AUTHOR]

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Laser-induced backside wet etching using water solution of plasmon precursor (AgNO3) as an absorbing medium provides effective structuring of such a complex material as sapphire. At the same time, this process is accompanied by the formation of silver nanoparticles and a significant modification of a surface layer of sapphire. Hybrid plasmon structures are formed on the surface of sapphire. In this paper, the structure and phase composition of surface layer formed during the transformation of the materials in the process of etching have been studied using electron microscopy methods, electron diffraction, and EDX analysis; possibilities of creating of new plasmon nanostructures have been analyzed. [ABSTRACT FROM AUTHOR]

Glass is one of the most important technical surfaces for numerous applications in automotive, optical, and consumer industries. In addition, by producing textured surfaces with periodic features in the micrometre range, new functions can be created. Although laser-based methods have shown to be capable to produce structured materials in a wide amount of materials, due to its transparency large bandgap dielectrics can be only processed in a controlled manner by employing high-power ultra-short pulsed lasers, thus limiting the employable laser sources. In this article, an interference-based method for the texturing of soda-lime glass using a 15 ns pulsed (1 kHz repetition rate) infrared (1053 nm) laser is proposed, which allows fabricating different periodic patterns with micrometre resolution. This method consists on irradiating a metallic absorber (stainless steel) put in direct contact with the glass sample and inducing locally an etching process on the backside of the glass. Then, the produced plasma at the interference maxima positions leads to the local fabrication of well-defined periodic line-like and dot-like surface patterns. The produced patterns are characterised using white light interferometry and scanning electron microscopy. [ABSTRACT FROM AUTHOR]

Our research is devoted to the shrinkage and swelling of PMMA film after micro-structuring with ion beam lithography. 10 MeV O4+ ions were used in the experiment. Parallel lines of 1 mm in length and 10 μm in thickness were created. The number of scan cycles and ion fluence were varied. The influence of the irradiation regime on PMMA elemental composition in micro-structured parts and microstructure morphology were studied. It was shown that microstructures created in PMMA film undergo both shrinkage and swelling processes depending on both the scan speed and the fluence. For the same fluence, shrinkage appears at fast scan speeds and swelling at slow ones. The same phenomenon was found in relation to the fluence for the same scan speed. It was observed that PMMA film rupture caused by irradiation occurred prior to the start of the carbonization of the irradiated area. [ABSTRACT FROM AUTHOR]

Chocolate and green banana biomass (GBB) are nutritious foods that benefit well-being and health. GBB adds nutritional value, acceptance, and benefits due to its fiber content, resistant starch, and low glycemic index. Adding GBB to chocolate with high cocoa content (approx. 70%) was evaluated by physicochemical, microbiological, and sensory properties. Samples were analyzed for composition, plastic viscosity, sensory analysis, particle size, and water activity. The results showed that chocolates added with GBB have moisture, lipids, and mineral content values by the current legislation. Viscosity analysis showed that the studied formulations presented expected values for chocolate (2.44–4.79 Pa), not compromising the processing of tempering, molding, cooling, and demolding, demonstrating the feasibility of incorporating GBB into chocolates. The values of the average particle sizes were less than 25 μm in the chocolates and recommended in terms of the sensory aspect. The rheological measurements showed that the Casson plastic viscosity values are in the suggested chocolate range. Sensory analysis revealed that the sample with the highest content of GBB showed the highest acceptance and obtained 56% of purchase intent. Adding GBB to chocolate did not change the physicochemical, microbiological, or sensory characteristics and made the product healthier for consumers. [Display omitted] • Preparation of high cocoa-content chocolate with green banana biomass. • Sensory analysis proved chocolates with GBB had high acceptance and purchase intent. • Adding GBB into chocolates increased nutritional value and decreased sugar content. [ABSTRACT FROM AUTHOR]

Ion micro beam was employed to fabricate microstructures based on poly(dimethylsiloxane) (PDMS). Carbon ions with energy of 6.0 MeV were used. The ion treatment induces modifications in PDMS surface and on the optical properties as a function of the ion current and fluence. PDMS foils were produced from commercially available two component addition materials. The selective modifications of the polymer were studied for applications in micro-fluids, micro-optics and micro-electronics. The comparison between the unirradiated and irradiated PDMS was investigated in morphology and compactness using the atomic force microscopy. The wetting ability of the PDMS surface was also analyzed as a function of the ion microbeam irradiation. The compositional and optical changes in PDMS were monitored by Rutherford backscattering spectrometry, elastic recoil detection analysis and optical spectroscopy measurements. [ABSTRACT FROM AUTHOR]

The metal–organic framework (MOF) HKUST‐1 was employed as an interaction matrix for fundamental loading studies of anthraquinone dyes. Chosen dyes were alizarin (A), alizarin S (AS), disperse blue 1 (B1), disperse blue 3 (B3), disperse blue 56 (B56) and purpurin (P). All materials were characterized by XRD, FTIR, TGA and SEM. Hence the interaction of dyes with the framework was characterized by theoretical–experimental differential analysis. One‐pot loading strategy resulted in more efficient scavenging of dyes, and reached 100 % for B56 using 50 mg L−1. SEM revealed important microstructural changes, the smaller crystals ranged 0.8–3 μm in size and almost all composite sizes were from this to higher values, reaching 70 μm, with varying shapes. Two composites were larger in size range (about 2500–1000 μm), and were shaped as rods, octahedrons and coffin lids. Indeed, the microstructure could be modulated depending on preparation conditions and type of loaded dye. For the higher loading series, N2 adsorption and XPS experiments were carried on to further evidence dye–MOF interactions. Ab initio prediction of structural properties for A@HKUST‐1 and P@HKUST‐1 were obtained by means of solid‐state CRYSTAL14 code at the PBE0 level of theory. Computed findings evidenced two O→Cu coordinative bonds, one from O‐ketone and the other from O‐phenolate moiety as main interactions towards CuNET centers. The dye is cast: The metal–organic framework (MOF) HKUST‐1 was employed as an interaction matrix for fundamental loading studies of anthraquinone dyes (e.g. alizarin in the picture). The interaction of dyes with the framework was characterized by theoretical–experimental differential analysis. A microstructural changes were encountered. [ABSTRACT FROM AUTHOR]

Sol-gel based layers doped with Rhodamine B phosphors (RB) were directly microstructured to produce sub-lambda 2D gratings, using nanoimprint lithography. Such an approach enables the simplification of technological processes, since no further etching process is required, which reduces considerably the number of technological steps and thus production costs. Surface microstructuring improved fluorophore emission in the visible range. Demonstrations were performed experimentally and samples were characterized using angle-resolved fluorescence. The emissions measured on microstructured luminescent coatings were 3–4 times higher, depending on the angle of observation, than those recorded on flat surfaces. This technological approach is very promising for the next generation of low-cost, high-performance anti-counterfeiting marking processes and for the traceability of objects based on unique optical effects. [Display omitted] • Variations in photoluminescence quantum yields as a function of excitation wavelength and RB concentrations were studied • The nanoimprint lithography technique was used to produce a 2D grating on a luminescent (TEOS/MTEOS)/RB base sol-gel coating. • Surface microstructuring improved fluorophore emission in the visible range. • Angle-resolved photoluminescence was investigated on the luminescent films with and without grating. [ABSTRACT FROM AUTHOR]

The microstructuring of surfaces is a highly researched field that is aimed at enhancing the tribological behavior of sliding surfaces such as artificial joints, which are subject to wear. Lubrication of the joint interface plays a key role in the wear process, although the mechanisms of lubrication are quite complex. In order to improve the lubrication, the surfaces of the articulating components can be modified by pulsed femtosecond-laser microstructuring. Through microstructuring, the apparent dynamic viscosity of the synovial fluid between the artificial joint can be increased due to its non-Newtonian properties. This may lead to better hydrodynamic lubrication and, therefore, reduced particle abrasion. Femtosecond laser-induced microstructures were investigated in a modified rheometer setup featuring a reduced gap size in order to reproduce and measure the interface between fluid and implant surface more accurately. As a test fluid, a synovial fluid substitute was used. The study has shown that an increase in the viscosity of the synovial fluid substitute can be achieved by microstructuring. Compared to a smooth implant surface, the apparent viscosity of the synovial fluid substitute increased by over 30% when ring-shaped microstructures of 100 µm diameter with an aspect ratio of 0.66 were implemented.

Subject of Study. The surface structure of the silicon wafers (substrate) with a thermally grown silicon dioxide on the surface (of SiO2/Si) is studied after irradiation by pulse fiber laser of ILI-1-20 type. The main requirements for exposure modes of the system are: the preservation of the integrity of the film of silicon dioxide in the process of microstructuring and the absence of interference of surrounding irradiated areas of the substrate. Method. Studies were carried out on silicon wafers KEF-4,5 oriented in the crystallographic plane (111) with the source (natural) silicon dioxide (SiO2) with thickness of about 4 nm, and SiO2 with 40 nm and 150 nm thickness, grown by thermal oxidation in moist oxygen. Also, wafers KHB-10 oriented in the plane (100) with 500 nm thickness of thermal oxide were investigated. Irradiation of SiO2/Si system was produced by laser complex based on ytterbium fiber pulse laser ILI-1-20. Nominal output power of the laser was 20 W, and the laser wavelength was λ = 1062 nm. Irradiation was carried out by a focused beam spot with a diameter of 25 microns and a pulse repetition rate of 99 kHz. The samples with 150 nm and 40 nm thickness of SiO2 were irradiated at a power density equal to 1,2·102 W/cm2, and the samples of SiO2 with 500 nm thickness were irradiated at a power density equal to 2,0·102 W/cm2. Scanning was performed using a two-axis Coordinate Scanning Device based on VM2500+ drives with control via a PC with the software package "SinMarkTM." Only one scan line was used at the maximum speed of the beam equal to 8750 mm/s. Morphology control of the irradiated samples was conducted by an optical microscope ZeissA1M with high-resolution CCD array. A scanning probe microscope Nanoedicator of the NT-MDT company was used for structural measurements. Main Results. It has been shown that at a single exposure of high-frequency pulsed laser radiation on SiO2/Si system, with maintaining the integrity of the SiO2 film, similar symmetric microstructures are formed on the silicon surface. We suggest that the reason for their appearance is the reconstruction of the surface of the silicon arising in the process of recrystallization of the silicon melt surface in the irradiated region of the substrate. The morphology of these microstructures is due to several factors: crystallographic orientation of the plate, original (before the thermal oxidation) reconstruction of the plate surface, elastic stresses of SiO2/Si, laser treatment (thermal, corpuscular, wave). Exposure modes for the observed structures have been determined. Practical Relevance. For the first time in the microstructuring of SiO2/Si by fiber laser in the high-speed scanning mode, images of pieces have been obtained, which can indirectly imply that the reconstruction of atoms on the silicon substrate surface occurs before the thermal oxidation. Clearly marked localization of laser energy at selected irradiation modes enables to assert the possibility of detection and control of structural defects for the elements of semiconductor electronic devices.

Subject of research. The paper deals with research of the surface ablation for single-crystal silicon wafers and properties of materials obtained in response to silicon ablation while scanning beam radiation of pulse fiber ytterbium laser with a wavelenght λ = 1062 nm in view of variation of radiation power and scanning modes. Method. Wafers of commercial p-type conductivity silicon doped with boron (111), n-type conductivity silicon doped with phosphorus (100) have been under research with a layer of intrinsical silicon oxide having the thickness equal to several 10 s of nanometers and SiO2 layer thickness from 120 to 300 nm grown by thermal oxidation method. The learning system comprises pulse fiber ytterbium laser with a wavelenght λ = 1062 nm. The laser rated-power output is equal to 20 W, pulse length is 100 ns. Pulses frequency is in the range from 20 kHz to 100 kHz. Rated energy in the pulse is equal to 1.0 mJ. Scanning has been carried out by means of two axial scanning device driven by VM2500+ and controlled by personal computer with «SinMarkТМ» software package. Scanning velocity is in the range from 10 mm/s to 4000 mm/s, the covering varies from 100 lines per mm to 3000 lines per mm. Control of samples has been carried out by means of Axio Imager A1m optical microscope Carl Zeiss production with a high definition digital video camera. All experiments have been carried out in the mode of focused laser beam with a radiation spot diameter at the substrate equal to 50 μm. The change of temperature and its distribution along the surface have been evaluated by FLIR IR imager of SC7000 series. Main results. It is shown that ablation occurs without silicon melting and with plasma torch origination. The particles of ejected silicon take part in formation of silicon ions plasma and atmosphere gases supporting the plasmo-chemical growth of SiO2. The range of beam scanning modes is determined where the growth of SiO2 layer is observed. Beginning with scanning velocity equal to 2000 mm/s, the torch existence is not fixed visually; silicon oxide origination is stopped, and silicon particles with nanometer sizes are formed as a result of silicon destruction. The process of silicon destruction is followed by sounds of different frequency depending on scanning velocity. Practical significance. The surface ablation for single-crystal silicon has been shown for the first time ever to be influenced significally by such features of laser radiation as laser beam scanning velocity and the covering of scanning lines. Laser beam scanning modes of pulse fiber ytterbium laser with a wavelenght λ = 1062 nm have been found out providing the synthesis of nanostructured silicon dioxide particles or silicon nanoparticles.

Laser beam tightly focused inside single-crystal diamond allows conducive microstructures to be fabricated via local phase transition of diamond to graphite. An extended modified region is formed in diamond due to propagation of so called laser-induced graphitization wave, which occurs immediately after the optical breakdown and propagates towards the laser beam even though the position of the laser focus is fixed. This paper is the first to consider the behavior of the graphitization wave when the laser focus uniformly moves towards the laser, which results in the formation of conductive wires of unlimited length in diamond. It has been found that there is an initial transitional period in the wire growth, during which velocities of the laser focus and the wire front are equalized owing to the change in the distance between them. After stabilization of the graphitization front velocity, the axial fluence at the front of the growing wire also reaches a constant value. It has been found that the stable laser fluence at the wire front is practically independent of the laser pulse energy, but it grows with increasing velocity of the laser focus. Such increase finally leads to violation of the physical criterion of the continuous wire growth, since the axial fluence at the wire front becomes higher than the diamond breakdown threshold. It has been shown that the minimal fluence providing propagation of the graphitization wave in diamond can be used to predict the lateral wire dimension. [ABSTRACT FROM AUTHOR]

Abstract A key requirement in automotive industry is reducing weight through innovative lightweight construction concepts. For multi-material construction the manufacture of plastic-metal hybrids poses a particular challenge due to the chemical and physical dissimilarity. At Fraunhofer ILT, a process chain has been developed for connecting thermoplastics with metals. First, the metal surface is microstructured with laser radiation to create undercut structures for the interlocking of polymer and metal, which are connected afterwards via a thermal joining process. Although laser-microstructuring is already a fast process, for automotive cycle times higher processing speeds are required. In this contribution a new polygon-based scanning system is combined with a 2 kW single mode fiber laser for a continuous high-speed microstructuring process of metals as pretreatment for local UD-tape-reinforcements. The scanner setup and first microstructuring results on different metals are presented. [ABSTRACT FROM AUTHOR]

Laser Induced Periodic Surface Structures (LIPSS) can be reliably produced using ultra-short laser pulses from 10 fs up to 10 ps, though it is a very time-consuming process. As the processing speed scales with the average power, the use of nanosecond-pulsed lasers can be cost-effective and reduce processing time, especially for industry requirements of treating large surface areas. In this work, we studied the influence of irradiation parameters and surface finishing in LIPPS efficient generation using a 100 ns nanosecond pulsed laser on AISI 304 stainless steel. Diffracted light intensity was used to evaluate the LIPSS quality and homogeneity in large surface areas, allowing the determination of process parameters interval for different initial surface roughness in a simple and fast way. The most efficient and uniform LIPSS were generated at 49 nm initial surface roughness, with single spot fluences varying from 3 J/cm 2 to 4 J/cm 2 and 83% beam overlapping, with only one or two successive scans. Processing speed as high as 50 mm 2 /s was obtained with a single scan at the maximum single spot fluence tested (4 J/cm 2 ), showing the potential use of nanosecond pulse lasers in industrial practical applications. [ABSTRACT FROM AUTHOR]

The method of thermoplasmonic laser-induced backside wet etching (TPLIBWE) is applied for effective and well-controlled microstructuring of sapphire. The method is based on the generation of highly absorbing silver nanoparticles in the course of the pulsed-periodic laser irradiation. The silver nanoparticles are formed as a result of the reduction of a water-dissolved precursor, AgNO3. The process of sapphire etching occurs via the formation of supercritical water at ultrahigh temperatures and pressures (which significantly exceed the critical values for water) and the formation of silver nanoparticles at the sapphire/water interface as a result of the absorption of laser radiation. The mechanism of TPLIBWE is considered and the etching rate, which reaches ~100 nm/pulse, is determined. The formation of aluminum nanoparticles, which indicates a deep destruction of Al2O3 as a result of TPLIBWE, is observed. [ABSTRACT FROM AUTHOR]