Line-like Patterns Research Articles

Influence of chemistry and topography on the wettability of copper

To understand the complex interplay of topography and surface chemistry in wetting, fundamental studies investigating both parameters are needed. Due to the sensitivity of wetting to miniscule changes in one of the parameters it is imperative to precisely control the experimental approach. A profound understanding of their influence on wetting facilitates a tailored design of surfaces with unique functionality.We present a multi-step study: The influence of surface chemistry is analyzed by determining the adsorption of volatile carbonous species (A) and by sputter deposition of metallic copper and copper oxides on flat copper substrates (B). A precise surface topography is created by laser processing. Isotropic topography is created by ps laser processing (C), and hierarchical anisotropic line patterns are produced by direct laser interference patterning (DLIP) with different pulse durations (D).Our results reveal that the long-term wetting response of polished copper surfaces stabilizes with time despite ongoing accumulation of hydrocarbons and is dominated by this adsorption layer over the oxide state of the substrate (Cu, CuO, Cu2O). The surfaces’ wetting response can be precisely tuned by tailoring the topography via laser processing. The sub-pattern morphology of primary line-like patterns showed great impact on the static contact angle, wetting anisotropy, and water adhesion. An increased roughness inside the pattern valleys combined with a minor roughness on pattern peaks favors air-inclusions, isotropic hydrophobicity, and low water adhesion. Increasing depth of the primary topography can also induce air-inclusions despite increasing peak roughness while time dependent wetting transitions were observed.

Surface Modification of Brass via Ultrashort Pulsed Direct Laser Interference Patterning and Its Effect on Bacteria-Substrate Interaction.

In recent decades, antibiotic resistance has become a crucial challenge for human health. One potential solution to this problem is the use of antibacterial surfaces, i.e., copper and copper alloys. This study investigates the antibacterial properties of brass that underwent topographic surface functionalization via ultrashort pulsed direct laser interference patterning. Periodic line-like patterns in the scale range of single bacterial cells were created on brass with a 37% zinc content to enhance the contact area for rod-shaped Escherichia coli (E. coli). Although the topography facilitates attachment of bacteria to the surface, reduced killing rates for E. coli are observed. In parallel, a high-resolution methodical approach was employed to explore the impact of laser-induced topographical and chemical modifications on the antibacterial properties. The findings reveal the underlying role of the chemical modification concerning the antimicrobial efficiency of the Cu-based alloy within the superficial layers of a few hundred nanometers. Overall, this study provides valuable insight into the effect of alloy composition on targeted laser processing for antimicrobial Cu-surfaces, which facilitates the thorough development and optimization of the process concerning antimicrobial applications.

Multi-Scale Structuring of CoCrMo and AZ91D Magnesium Alloys Using Direct Laser Interference Patterning

In this work, the technique of Direct Laser Interference Patterning (DLIP) was used to fabricate micrometric structures at the surface of Cobalt-Chromium-Molybdenum and AZ91D magnesium alloys. Line-like patterns with spatial periods of 5 μm were textured using an ultra-short pulsed laser (10 ps pulse duration and 1064 nm wavelength) with a two-beam interference setup. The surface topography, morphology, and chemical modifications were analysed using Confocal Microscopy, Scanning Electron Microscopy, and Energy Dispersive Spectroscopy (EDS), respectively. Laser fluence and pulse overlap were varied to evaluate their influence on the final structure. Homogeneous structures were achieved for the CoCrMo alloy for every condition tested, with deeper structures (up to 0.85 μm) being achieved for higher energy levels (higher overlap and/or fluence). For high energy, sub-micrometric secondary structures, so-called LIPSS, could also be observed on the CoCrMo. The EDS analysis showed some oxidation after the laser texturing. Regarding the AZ91D alloy, deeper structures could be achieved (up to 2.5 μm), but more melting and oxidation was observed, forming spherical oxide particles. Nonetheless, these results bring new perspectives on the fabrication of microtextures on the surface of CoCrMo and AZ91D using DLIP.

Heating influence on hierarchical structures fabricated by direct laser interference patterning

The combination of direct laser interference patterning (DLIP) with laser-induced periodic surface structures (LIPSS) enables the fabrication of functional surfaces reported for a wide spectrum of materials. The process throughput is usually increased by applying higher average laser powers. However, this causes heat accumulation impacting the roughness and shape of produced surface patterns. Consequently, the effect of substrate temperature on the topography of fabricated features requires detailed investigations. In this study, steel surfaces were structured with line-like patterns by ps-DLIP at 532 nm. To investigate the influence of substrate temperature on the resulting topography, a heating plate was used to adjust the temperature. Heating to 250 ^{circ }C led to a significant reduction of the produced structure depths, from 2.33 to 1.06 µm. The reduction is associated with the appearance of a different LIPSS type, depending on the grain orientation of the substrates and laser-induced superficial oxidation. This study revealed a strong effect of substrate temperature, which is also to be expected when heat accumulation effects arise from processing surfaces at high average laser power.

Construction and Configuration Analysis of Zelkova Serrata Lenticel-Like Patterns Generated through DNA Algorithmic Self-Assembly.

Multiple models and simulations have been proposed and performed to understand the mechanism of the various pattern formations existing in nature. However, the logical implementation of those patterns through efficient building blocks such as nanomaterials and biological molecules is rarely discussed. This study adopts a cellular automata model to generate simulation patterns (SPs) and experimental patterns (EPs) obtained from DNA lattices similar to the discrete horizontal brown-color line-like patterns on the bark of the Zelkova serrata tree, known as lenticels [observation patterns (OPs)]. SPs and EPs are generated through the implementation of six representative rules (i.e., R004, R105, R108, R110, R126, and R218) in three-input/one-output algorithmic logic gates. The EPs obtained through DNA algorithmic self-assembly are visualized by atomic force microscopy. Three different modules (A, B, and C) are introduced to analyze the similarities between the SPs, EPs, and OPs of Zelkova serrata lenticels. Each module has unique configurations with specific orientations allowing the calculation of the deviation of the SPs and the EPs with respect to the OPs within each module. The findings show that both the SP and the EP generated under R105 and R126 and analyzed with module B provide a higher similarity of Zelkova serrata lenticel-like patterns than the other four rules. This study provides a perspective regarding the use of DNA algorithmic self-assembly for the construction of various complex natural patterns.

Role of Superb Microvascular Imaging in Differentiating Between Malignant and Benign Solid Breast Masses

IntroductionThe purpose of this study was to evaluate the diagnostic performance of superb microvascular imaging (SMI) in breast lesions. Materials and MethodsEighty-five solid breast lesions were studied with color Doppler flow imaging (CDFI), power Doppler imaging (PDI), monochromatic SMI (mSMI), and contrast-enhanced ultrasonography (CEUS). The penetrating vessels (PVs) and microvascular morphologic and distribution features of the breast tumors were evaluated for each modality. ResultsThe diagnostic accuracies of CDFI, PDI, mSMI, and CEUS were calculated and compared. Surgical pathologic analysis showed 47 benign and 38 malignant lesions. Compared with CDFI and PDI, mSMI and CEUS detected more PVs in breast lesions. The microvascular architecture showed significant differences between benign and malignant lesions. Benign lesions mainly displayed avascular, line-like, and branch-like patterns, and malignant lesions tended to display root hair-like and crab claw-like patterns. mSMI and CEUS identified more root hair-like and crab claw-like patterns in malignant lesions than CDFI and PDI. The sensitivity, negative predictive value, and accuracy of mSMI findings in diagnosing malignancy based on PVs and vascular patterns were both higher than those of CDFI and PDI. ConclusionsmSMI is equal to CEUS and superior to CDFI and PDI in identifying microvascular and discriminating malignant and benign breast masses.

Interference-based laser-induced micro-plasma ablation of glass

AbstractGlass 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.

Laser interference patterned ta-C-coated dry forming tools

PurposeThis study aims to introduce a strategy that permits well-defined contact areas in forming tools for improving both wear and friction properties by a selective laser treatment of a hydrogen-free diamond-like carbon layer (DLC), for substituting lubrication in forming processes. The need of lubricant substitution in forming processes is given because, besides the positive technological aspects, lubrication leads to numerous negative economic and ecological effects such as lubricant appliance and removal costs as well as its disposal.Design/methodology/approachHydrogen-free DLCs with an sp³-ratio of 60-70 per cent are deposited on steel surfaces and subsequently micro-structured using direct laser interference patterning (DLIP). To find the optimal structure parameters for reducing friction and wear, line-like and cross-like patterns with three different structure sizes were fabricated onto the DLC layer. Tribological measurements are performed with a ball-on-disk tribometer on the differently DLIP-structured surfaces and compared to polished steel and unstructured DLC reference surfaces.FindingsA reduction of the coefficient of friction, from 0.18 to 0.11, is observed for the laser-structured DLC surfaces, reaching values comparable to lubricated and polished steel surfaces, with a friction coefficient of 0.10.Originality/valueUsing DLIP, it was possible to show how this method can reduce friction on DLC-coated specimens. The observed characteristics are relevant to improve the tribological performance of forming processes, without usage of lubrication.

Development of a Monitoring Strategy for Laser-Textured Metallic Surfaces Using a Diffractive Approach.

The current status of research around the world concurs on the powerful influence of micro- and nano-textured surfaces in terms of surface functionalization. In order to characterize the manufactured topographical morphology with regard to the surface quality or homogeneity, major efforts are still required. In this work, an optical approach for the indirect evaluation of the quality and morphology of surface structures manufactured with Direct Laser Interference Patterning (DLIP) is presented. For testing the designed optical configuration, line-like surface patterns are fabricated at a 1064 nm wavelength on stainless steel with a repetitive distance of 4.9 µm, utilizing a two-beam DLIP configuration. Depending on the pulse to pulse overlap and hatch distance, different single and complex pattern geometries are produced, presenting non-homogenous and homogenous surface patterns. The developed optical system permitted the successfully classification of different pattern geometries, in particular, those showing single-scale morphology (high homogeneity). Additionally, the fabricated structures were measured using confocal microscopy method, and the obtained topographies were correlated with the recorded optical images.

Spatio-temporal sEMG image enhancement and motor unit action potential (MUAP) detection: algorithms and their analysis

In spatiotemporal multi-channel surface electromyogram (EMG) images where the x-axis is time, the y-axis is EMG channels and the gray level is EMG amplitude, the motor unit action potential (MUAP) appears as a linear Gaussian structure. The appearance of this MUAP pattern in the spatiotemporal images is mostly distorted either by the destructive superposition of other MUAPs occurring in the conducting volume or by various noises such as a power line, bad electrode and skin contacts and movement artifacts. For accurate automatic detection of MUAP, EMG image enhancement is needed to suppress the background noises and enhance the line-like MUAP propagation patterns. This study presents several candidate filters to enhance the MUAPs propagation pattern in spatiotemporal EMG images. The filters, which can detect and enhance line-like structure in digital images, are used. Specifically, the Hermite shape filter is used for EMG image enhancement and compared with Gabor filter and steerable filters. The performance of the filters regarding accuracy, specificity, and sensitivity is evaluated with real sEMG signal measured from different muscles and computer-generated EMG signals. In the enhanced images the visibility of the MUAP region is improved. These results can help in better estimation of muscle characteristics from sEMG signals.

On the Interplay of DLIP and LIPSS Upon Ultra-Short Laser Pulse Irradiation.

Controlling laser induced surface morphology is essential for developing specialized functional surfaces. This work presents novel, multi-scale periodic patterns with two-dimensional symmetry generated on stainless steel, polyimide and sapphire. The microstructures were realized by combining Direct Laser Interference Patterning with the generation of Laser Induced Periodic Surface Structures in a one-step process. An industrial, fiber femtosecond laser source emitting at 1030 nm with a pulse duration of 500 fs was utilized for the experiments. In the case of stainless steel, it was possible to create line-like or pillar-like surface patterns by rotating the polarization orientation with respect to the interference pattern. In the case of polyimide and sapphire, the absorption of the laser radiation was promoted by a multiphoton mechanism. In polyimide, grooves and pillars of several microns in depth were produced over an area much larger than the spot size. Finally, for sapphire, the simultaneous generation of interference-like pattern and laser induced periodic surface structures was realized. The results reported here provide valuable data on the feasibility to combine two state-of-the-art techniques with an industrial apparatus, to control the induced surface morphology.

Multiple method micromachining laser platform for fabricating anti-counterfeit elements with multiple-scaled features

Textured metallic parts with multiple-scaled micro-structures have significant advantages for anti-counterfeit applications. For this purpose, the development of an automatized micromachining laser-platform is introduced, which is capable of handling different laser based fabrication methods including direct laser writing (DLW) and direct laser interference patterning (DLIP), using only one laser source (Nd:YAG laser, 1064 nm wavelength, 500 ps pulse duration). Using DLW, line, cross-like and rectangular structures with length scales from 50 to 150 µm were produced, while DLIP was used to produce line-like patterns structures, with 3.7 and 25 µm spatial periods. In addition, laser induced periodic surface structures (LIPSS) were also combined and thus obtaining hierarchical patterns with three different length scales in one process. Finally, additional samples were automatically structured to produce examples of definable security features at the touch of a button. The surface topography of the treated samples is analyzed using scanning electron microscopy, optical microscopy and white light interferometry methods.

Effects of laser surface texturing on tribological properties of Ti-6Al-4V in hydroxyethyl-cellulose water-based lubrication

PurposeThis paper aims to investigate the effect of laser surface texturing on the tribological performance of Ti-6Al-4V disks sliding against Si3N4 balls under hydroxyethyl-cellulose water-based lubrication. The friction coefficients and wear losses of textured and untextured disks were measured and compared. The results indicate that the texture patterns can lead to reduction of friction and wear in the condition of water-based lubrication.Design/methodology/approachSolutions of hydroxyethyl cellulose were used as water-based lubricants. To find the optimal laser texturing parameters for the best performance enhancement, three line-like patterns were fabricated onto the disks and three machining parameters were used for each type of pattern. Tribological tests were conducted in rotation sliding with ball-on-disk contact configuration on UMT-2.FindingsA higher density of texture lines leads to a larger friction and wear reduction. Compared with untextured disks, the friction coefficient is reduced from 0.043 to 0.028 for textured disks. Some unworn parts were detected in the contact region of the balls against textured disks, which were not found on the balls against untextured disks. The worn surfaces indicated that periodic geometry of the contact track was rebuilt during run-in period, which was beneficial for the formation of lubricant films.Originality/valueIn this work, laser surface texturing was used to reduce the friction and wear of Ti-6Al-4V specimens in water-based lubrication, which can be used to improve the tribological performance of Ti-6Al-4V components in mechanical equipment.

Streptavidin-Decorated Algorithmic DNA Lattices Constructed by Substrate-Assisted Growth Method.

The ultimate goal of DNA computing is to store information at higher density and solve complex problems with less computational time and minimal error. Most algorithmic DNA lattices have been constructed using the free-solution growth (FSG) annealing method, and hairpin-embedded DNA rule tiles have been introduced in most algorithmic implementations to differentiate 0- and 1-bit information. Here, we developed streptavidin (SA)-decorated algorithmic COPY (produced line-like patterns with biotinylated 1-bit rule tiles) and XOR (triangle-like patterns) lattices constructed by a substrate-assisted growth (SAG) method and FSG. SA decoration in algorithmic lattices provides an efficient platform for visualizing bit information, and the SAG method in algorithmic assembly offers full coverage of algorithmic lattices on a substrate with a relatively lower DNA concentration than previous methods. The algorithmic COPY and XOR lattices assembled with various ratios of 0- and 1-bit rule tiles were verified by atomic force microscopy. We found that even asymmetric DNA patterns produced by certain algorithmic logic gates could be easily constructed by SAG. Finally, we evaluated sorting factors and error rates of algorithmic COPY and XOR lattices to determine the bit population and quality of the algorithmic assembly. Because of the catalytic effect of the substrate, the sorting factor of algorithmic DX-DNA lattices did not greatly influence the specific rules (i.e., COPY and XOR logic gates) annealed by SAG. Additionally, we found that the overall error rates of algorithmic DX-DNA lattices prepared by the FSG and SAG methods were low, within the range of 1-3%. Hence, the self-assembled algorithmic patterns generated with DNA molecules may serve as a scaffold for molecular demultiplexing circuits and computing.

Influence of processing parameters on surface texture homogeneity using Direct Laser Interference Patterning

Surface functionalities in the field of tribology, wettability, biocompatibility and holographic marking introduced by well-defined surface structures strongly depend on the surface texture homogeneity and quality. This work presents strategies for the fabrication of homogeneous periodic surface microstructures employing the Direct Laser Interference Patterning (DLIP) technology with the fundamental transverse mode (TEM00) emitted from a nanosecond laser source. Ti6Al4V substrates are structured using line-like patterns with spatial periods of 7.20 µm, 5.82 µm and 4.31 µm. The impact of various DLIP process parameters such as laser fluence, pulse overlap, hatch distance and spatial period on the produced surface microstructures is introduced and the consequences on the surface texture homogeneity are discussed. Large-area analysis of micro structures is carried out through white light interferometry and scanning electron microscopy. A quantitative measurement scheme of the pattern homogeneity, based on topographical properties such as kurtosis, standard deviation and mean structure height was introduced. Furthermore, the influence of a second modulation arising from the employed hatch distance has been identified. A quantitative parameter, the surface error percentage, has been introduced and employed for the characterization of pattern homogeneity. It was found that specially for larger spatial periods and surfaces treated at high laser fluence, pulse-to-pulse overlaps and a short hatch distance, the overall surface texture homogeneity could be improved up to ∼80–90%.

3-Input/1-Output Logic Implementation Demonstrated by DNA Algorithmic Self-Assembly.

Although structural DNA nanotechnology is a well-established field, computations performed using DNA algorithmic self-assembly is still in the primitive stages in terms of its adaptability of rule implementation and experimental complexity. Here, we discuss the feasibility of constructing an M-input/ N-output logic gate implemented into simple DNA building blocks. To date, no experimental demonstrations have been reported with M > 2 owing to the difficulty of tile design. To overcome this problem, we introduce a special tile referred to as an operator. We design appropriate binding domains in DNA tiles, and we demonstrate the growth of DNA algorithmic lattices generated by eight different rules from among 256 rules in a 3-input/1-output logic. The DNA lattices show simple, linelike, random, and mixed patterns, which we analyze to obtain errors and sorting factors. The errors vary from 0.8% to 12.8% depending upon the pattern complexity, and sorting factors obtained from the experiment are in good agreement with simulation results within a range of 1-18%.

Microstructural and Metallurgical Assessment of the Laser-Patterned Cemented Tungsten Carbide (WC-CoNi)

Cemented carbide is difficult to machine using traditional chip-removal methods due to its hardness. Electrical discharge machining (EDM) is the common method applied to shape cemented carbides because high geometric precision can be achieved. However, some important defects (pores, residual stresses or oxidation products) can be induced due to thermal reactions. Ultra-short pulse laser processing can also provide high precision and meanwhile effectively avoid these defects due to its short laser-matter reaction time. In this paper, three different patterns on WC-CoNi cemented carbides for tribological purposes, namely line-like patterns, dimples and grooves, have been created using different laser set-ups with pulse duration in the range of nanoseconds (10-9s), picoseconds (10-12s) and femtoseconds (10-15s). Microstructural and metallurgical changes of modified surfaces have been studied. Laser scanning microscopy (LSM) is conducted to measure the pattern dimensions. Focused ion beam (FIB) in combination with scanning electron microscope (SEM) is used to investigate the microstructural changes of the patterned materials.

Endothelial cell responses to castor oil-based polyurethane substrates functionalized by direct laser ablation

Surface-induced thrombosis and lack of endothelialization are major drawbacks that hamper the widespread application of polyurethanes for the fabrication of implantable cardiovascular devices. Endothelialization of the blood-contacting surfaces of these devices may avoid thrombus formation and may be implemented by strategies that introduce micro and submicron patterns that favor adhesion and growth of endothelial cells. In this study, we used laser radiation to directly introduce topographical patterns in the low micrometer range on castor oil-based polyurethane, which is currently employed to fabricate cardiovascular devices. We have investigated cell adhesion, proliferation, morphology and alignment in response to these topographies. Reported results show that line-like and pillar-like patterns improved adhesion and proliferation rate of cultured endothelial cells. The line-like pattern with 1 μm groove periodicity was the most efficient to enhance cell adhesion and induced marked polarization and alignment. Our study suggests the viability of using laser radiation to functionalize PU-based implants by the introduction of specific microtopography to facilitate the development of a functional endothelium on target surfaces.

Frictional Performance Assessment of Cemented Carbide Surfaces Textured by Laser

Cemented carbides are advanced engineering materials often used in industry for manufacturing cutting tools or supporting parts in tribological system. In order to improve service life, special attention has been paid to change surface conditions by means of different methods, since surface modification can be beneficial to reduce the friction between the contact surfaces as well as to avoid unintended damage. Laser surface texturing is one of the newly developed surface modification methods. It has been successfully introduced to fabricate some basic patterns on cemented carbide surfaces. In this work, Direct Laser Interference Patterning Technique (DLIP) is implemented to produce special line-like patterns on a cobalt (Co) and nickel (Ni) based cemented tungsten carbide grade. It is proven that the laser-produced patterns have high geometrical precision and quality stability. Furthermore, tribology testing using a nano-tribometer unit shows that friction is reduced by the line-like patterns, as compared to the polished one, under both lubricated and dry testing regimes, and the reduction is more pronounced in the latter case.

Low Friction and High Solid-Solid Contact Ratio—A Contradiction for Laser-Patterned Surfaces?

Recording of Stribeck-like curves is a common way to study the effect of laser-patterned surfaces on the frictional efficiency. However, solely relying on the coefficient of friction when identifying the lubrication regime and the underlying working principles can be misleading. Consequently, a ball-on-disc tribometer was combined with an electrical resistivity circuit to simultaneously measure Stribeck-like curves and solid-solid contact ratios for polished and laser-patterned samples. Line-like surface patterns with different periodicities were produced by direct laser interference patterning on steel substrates (AISI304). The reference shows a Stribeck-like behavior well correlating with the contact ratios. The behavior deviates for high sliding velocities (high contact ratios) due to a loss of lubricant induced by centrifugal forces pulling the lubricant out of the contact zone. In contrast, the solid–solid contact ratio of the laser-patterned samples is around 80% for all sliding velocities. Those values can be explained by higher contact pressures and the structural depth induced by the surface topography which make a full separation of the surfaces unlikely. Despite those high values for the contact ratio, laser-patterning significantly reduces friction, which can be traced back to a reduced real contact area and the ability to store oil in the contact zone.