Pattern Geometry Research Articles

Numerical Bifurcation Analysis of a Film Flowing over a Patterned Surface through Enhanced Lubrication Theory

The bifurcation analysis of a film falling down an hybrid surface is conducted via the numerical solution of the governing lubrication equation. Instability phenomena, that lead to film breakage and growth of fingers, are induced by multiple contamination spots. Contact angles up to 75∘ are investigated due to the full implementation of the free surface curvature, which replaces the small slope approximation, accurate for film slope lower than 30∘. The dynamic contact angle is first verified with the Hoffman–Voinov–Tanner law in case of a stable film down an inclined plate with uniform surface wettability. Then, contamination spots, characterized by an increased value of the static contact angle, are considered in order to induce film instability and several parametric computations are run, with different film patterns observed. The effects of the flow characteristics and of the hybrid pattern geometry are investigated and the corresponding bifurcation diagram with the number of observed rivulets is built. The long term evolution of induced film instabilities shows a complex behavior: different flow regimes can be observed at the same flow characteristics under slightly different hybrid configurations. This suggest the possibility of controlling the rivulet/film transition via a proper design of the surfaces, thus opening the way for relevant practical application.

Laser Structured Gas Diffusion Layers for Improved Water Transport and Fuel Cell Performance

Polymer electrolyte fuel cells are promising energy converters for future green energy systems. For wide commercial use, still cost reductions by increasing the power density are required. Structurally optimized gas diffusion layers (GDLs), allowing for cell operation at high current densities with reduced mass transport losses, are an essential component for this development. Here we demonstrate that GDLs modified with perforations can improve water transport in the high current density regions and increase fuel cell performance. Laser perforation prior to GDL hydrophobization circumvents previously observed flooding problems and allows for stable operation. The advanced pattern, connecting channel and land regions drains pores, hence decreasing the liquid water fraction, especially close to the GDL and catalyst layer interface. Operando dynamic X-ray tomographic microscopy (XTM) is employed to understand water transport in the modified structure, and the competition with random break-through of water clusters to the channel is analyzed. The detailed and time-resolved insights allow us to propose guidelines for future advanced patterning geometries, suggesting denser perforations and methods to counteract the observed high frequency resistance (HFR) increase. Furthermore, this approach can act as model system for next generation GDLs and lead to a more rational design of transport layers.

Terahertz imaging with metamaterials for biological applications

Terahertz (THz) technology has become more widespread due to its diverse range of potential applications, particularly when combined with various functional metamaterials using cutting-edge nanotechnology techniques. In this report, we introduce a highly improved THz imaging technology by comparing complementary metamaterials intuitively based on Babinet’s principle. The THz reflectance spectra for the complementary metamaterials exhibit a significant and distinct association with the polarization angle. Four different polarization angles and metamaterial pattern geometries were tested for the reflectance imaging of a target image pattern. Field enhancement on the metamaterial surface was also investigated using finite element simulations to support the experimental results. Optimizing the metamaterial based on the experimental and calculation results led to high image contrast and quality. The proposed label-free imaging platform was then employed to produce clear contrast images for mouse brain tissue and HEK-293 cells, thus highlighting the potential application of this system to real biological samples.

Atomic Layer 3D Printing: Influence of Reactor Design and Pattern Geometry

As additive manufacturing in its various forms is shifting the paradigm of traditional manufacturing, the same space opens in the field of thin film deposition. Atomic layer deposition is, due to its inherent separation of reactions, uniquely suitable for adaptation into a 3D printer. In fact, the concept of spatial atomic layer deposition, which can be considered as a precursor for 3D atomic layer printing, goes all the way back to 1974.1 Despite the many challenges of creation and miniaturization of spatial ALD reactors, atomic layer 3D printing was successfully proved as a concept recently.2,3 Confining spatial ALD (atomic layer deposition) laterally to a spot with a size in the micron range allows one to perform ALD cycles by repeated passes of the deposition head above the substrate. The pattern defined by the motions of the deposition head may be arbitrarily complex. This concept allows for the definition of deposits in three dimensions in the manner of classical additive manufacturing (3D printing). However, the vertical resolution of the shapes generated is defined by the surface chemical principles of ALD, and therefore is on the order of single atoms. The lateral resolution depends on the printing head and the gas flows and is currently on the order of hundreds of μm.We have demonstrated the self-limiting behavior of this atomic-layer additive manufacturing (ALAM) procedure for several materials. Under atmospheric conditions, the deposition of TiO2 occurs with the same growth per pass as in conventional ALD. The cross-section of a deposit exhibits a horizontal surface and sharp edges. The self-limiting behavior of the surface chemistry is maintained. As an example of a noble metal, Pt grows in a highly crystalline and even oriented form. Air-sensitive precursors such as the metal alkyls can be handled safely in aerobic conditions, and the growth of Al2O3 and ZnO occurs with familiar characteristics.Thus, ALAM is a novel method allowing for the direct generation of multimaterial structures without the need for preliminary or subsequent patterning. However, for the best performance of atomic layer 3D printing, the influence of geometry of both the reactor and the pattern being printed has to be examined. Generally, due to the necessary spatial separation of precursor and reactant, edge effects are necessarily present. Moreover, deviations from the perfect printing geometry cause additional line edge effects and selectivity defects. Additionally, we created a general theoretical model of effects caused by spatial separation on the printed pattern. The theoretical model was then confronted with experiments performed on the atomic layer 3D printer developed by ATLANT 3D Nanosystems. The theoretical effects and samples analyzed include edges of lines, overlaps of lines including rastering and gradients, multiple paths overlaps during pattern printing and step pattern printing. To prove that these effects are independent of the specific material, the effects are explored for TiO2, ZnO, and Pt.[1] Tuomo Suntola, Jorma Antson. Method for producing compound thin films. US4058430A, United States Patent and Trademark Office, 29 November 1974.[2] Ivan Kundrata, Maksym Plakhotnyuk, Maïssa K. S. Barr, Sarah Tymek, Karol Fröhlich, Julien Bachmann (2020, June 30) An Atomic-Layer 3D Printer [Conference presentation] ALD/ALE 2020[3] Cesar Arturo Masse de la Huerta, Viet H. Nguyen, Abderrahime Sekkat, Chiara Crivello, Fidel Toldra-Reig, Pedro Veiga, Carmen Jimenez, Serge Quessada, David Muñoz-Rojas. Facile patterning of functional materials via gas-phase 3D printing [2020, Cornell University Condensed Matter, Materials Science] Figure 1

Robust sclera recognition based on a local spherical structure

The sclera is the opaque white tissue that covers the sphere of the human eye, and this causes a complex nonlinear deformation of the vessel pattern in the sclera as the eyes move. Over the last decade, although the blood vessels of the sclera have been investigated for use as a biometric modality, very little research has been undertaken on feature extraction and matching based on this anatomical structure. To address this problem, we propose a new local spherical structure (LSS) that incorporates a vessel shape feature (VSF) to represent the geometry and texture feature of the vessel pattern. The key ideas in this work are the designs of the VSF and the LSS, which are based on the fact that the vessels lie below a sphere-shaped sclera. To create the proposed VSF, a Harris corner detector is used to extract interest points, each of which is encoded into a normalized polar histogram that represents the shape of a vessel. These points are then projected onto the surface of a sphere, and we design an LSS to represent the topological relationships between each of the points, derived from the arc distance. In the matching step, we adopt a coarse-to-fine procedure that enables a fast similarity comparison between two point pairs using the VSF and the LSS. The final matching score is obtained by combining the number of matched pairs, the total number of interest points, and the similarity. Various experiments were conducted on the UBIRIS.v1 and UTIRIS databases, the latter of which was more challenging. The proposed method showed promising performance, as it yielded an error rate equal to those of other feature extraction and matching methods. Our findings suggest that the proposed approach not only outperforms the state-of-the-art methods of sclera recognition but also illustrates how to address the issue of nonlinear deformation of the vessel pattern based on the anatomical structure of the human eye.

Density Functional Theory-Inspired Design of Ir/P,S-Catalysts for Asymmetric Hydrogenation of Olefins

In silico-based optimization of Ir/P,S-catalysts for the asymmetric hydrogenation of unfunctionalized olefins using (E)-1-(but-2-en-2-yl)-4-methoxybenzene as a benchmark olefin has been carried out. DFT calculations revealed that the thioether group has a major role in directing the olefin coordination. This, together with the configuration of the biphenyl phosphite group, has an impact in maximizing the energy gap between the most stable transition states leading to opposite enantiomers. As a result, the optimized catalyst proved to be efficient in the hydrogenation of a range of alkenes with the same substitution pattern and olefin geometry as the benchmark olefin, regardless of the presence of functional groups with different coordination abilities (ee values up to 97%). Appealingly, further modifications at the thioether groups and at the biaryl phosphite moiety allowed the highly enantioselective hydrogenation of olefins with different substitution patterns (e.g., α,β-unsaturated lactones and lactams, 1,1′-disubstituted enol phosphinates, and cyclic β-enamides; ee values up to >99%).

Demoulding process assessment of elastomers in micro-textured moulds

Background: Micro-texturing is an increasingly used technique that aims at improving the functional behaviour of components during their useful life, and it is applied in different industrial manufacturing processes for different purposes, such as reducing friction on dynamic rubber seals for pneumatic equipment, among others. Micro-texturing is produced on polymer components by transfer from the mould and might critically increase the adhesion and friction between the moulded rubber part with the mould, provoking issues during demoulding, both on the mould itself and on the rubber part. The mould design, the coating release agent applied to the mould surface, and the operational parameters of the moulding/demoulding process, are fundamental aspects to avoid problems and guarantee a correct texture transfer during the demoulding process. Methods: In this work, the lack of knowledge about demoulding processes was addressed with an in-house test rig and a robust experimental procedure to measure demoulding forces (DFs) as well as the final quality of the moulded part, between thermoset polymers and moulds. After the characterization of several Sol-Gel coating formulations (inorganic; hybrid) the influence of several parameters was analysed experimentally, i.e.: Sol-Gel efficiency, texture effects, pattern geometry, roughness and material compound. Results: The results obtained from the experimental studies revealed that texture depth is the most critical geometrical parameter, showing high scatter among the selected compounds. Finally, the experimental results were used to compute a model through reduced order modelling (ROM) technique for the prediction of DFs. Conclusions: The characterization of DFs in a laboratory, with a specific device operated by a universal testing machine (UTM), provided valuable information that allows a fast and optimized introduction of texturing in rubber components. Selection of a novel Sol-Gel coating and the use of the ROM technique contributed to speed up implementation for mass production.

Effect of Laser Surface Texturing on Coating Adherence and Tribological Properties of CuNiIn and MoS2 Coating

Copper nickel indium (CuNiIn) and Molybdenum disulphide (MoS2) duplex coating is used in aero engine compressor blades of Ti6Al4V to prevent fretting failure. Surface before coating is roughened by grit blasting process for coating adhesion. In present study, in place of grit blasting, laser surface texturing (LST) process is used for surface preparation and compared with grit blasted surface. Four different elliptical and square patterns are created by LST on Ti6Al4V. Difference of surface topography between LST and grit blasted surface is analyzed by SEM and white light interferometery. CuNiIn is deposited on Ti6Al4V by atmospheric plasma spray. MoS2 lubricating coating is deposited on top of CuNiIn by spray painting and curing. Effect of difference in surface preparation on coating microstructure as well as on tribological properties is studied. The results showed that geometry and dimensions of LST pattern influence the coating adherence and wear performance. LST process can be optimized for better performance and explored as an alternative surface preparation process in industry for thermal spray coatings.

Faceting of Si and Ge crystals grown on deeply patterned Si substrates in the kinetic regime: phase-field modelling and experiments

The development of three-dimensional architectures in semiconductor technology is paving the way to new device concepts for various applications, from quantum computing to single photon avalanche detectors. In most cases, such structures are achievable only under far-from-equilibrium growth conditions. Controlling the shape and morphology of the growing structures, to meet the strict requirements for an application, is far more complex than in close-to-equilibrium cases. The development of predictive simulation tools can be essential to guide the experiments. A versatile phase-field model for kinetic crystal growth is presented and applied to the prototypical case of Ge/Si vertical microcrystals grown on deeply patterned Si substrates. These structures, under development for innovative optoelectronic applications, are characterized by a complex three-dimensional set of facets essentially driven by facet competition. First, the parameters describing the kinetics on the surface of Si and Ge are fitted on a small set of experimental results. To this goal, Si vertical microcrystals have been grown, while for Ge the fitting parameters have been obtained from data from the literature. Once calibrated, the predictive capabilities of the model are demonstrated and exploited for investigating new pattern geometries and crystal morphologies, offering a guideline for the design of new 3D heterostructures. The reported methodology is intended to be a general approach for investigating faceted growth under far-from-equilibrium conditions.

Neural tuning and representational geometry.

A central goal of neuroscience is to understand the representations formed by brain activity patterns and their connection to behaviour. The classic approach is to investigate how individual neurons encode stimuli and how their tuning determines the fidelity of the neural representation. Tuning analyses often use the Fisher information to characterize the sensitivity of neural responses to small changes of the stimulus. In recent decades, measurements of large populations of neurons have motivated a complementary approach, which focuses on the information available to linear decoders. The decodable information is captured by the geometry of the representational patterns in the multivariate response space. Here we review neural tuning and representational geometry with the goal of clarifying the relationship between them. The tuning induces the geometry, but different sets of tuned neurons can induce the same geometry. The geometry determines the Fisher information, the mutual information and the behavioural performance of an ideal observer in a range of psychophysical tasks. We argue that future studies can benefit from considering both tuning and geometry to understand neural codes and reveal the connections between stimuli, brain activity and behaviour.

Tiny yet tough: Maximizing the toughness of fiber-reinforced soft composites in the absence of a fiber-fracture mechanism

Tiny yet tough: Maximizing the toughness of fiber-reinforced soft composites in the absence of a fiber-fracture mechanism

Effect of Respiratory Tract Disease on Particle Deposition.

This chapter describes the effects that respiratory disease has on particle deposition in the lungs. The geometry of airways, breathing patterns, and regional ventilation are all affected by various lung diseases, including COPD, asthma, and cystic fibrosis, and in turn modify total and regional deposition from normal. Total particle deposition in the lung is increased by airways obstruction and increased ventilation at rest compared to healthy individuals. Regional particle deposition is 1) shifted from distal to more proximal bronchial airways by airway obstruction, and 2) becomes more heterogeneous due to uneven lung ventilation. The net effect of the changes in total and regional particle deposition from normal is to greatly enhance bronchial airway surface doses for particle deposition while leaving unventilated lung regions inaccessible to the particles. As a result, both therapeutic aerosol delivery and the adverse effects of pollutant particles may be altered with progression of lung disease.

Cutting as an Innovative Approach to Surface and Textile Design

We live in an age where new technologies enable materials and techniques, hitherto unconventional for this field, to start being applied in the design of surfaces and textiles. One such technique is cutting. Used for the creation of works with high artistic value, the manual cutting of paper has been developed to the level of an autonomous art form: kirigami – the Japanese art of cutting paper. Inspired by the technique of kirigami, designers and artists today continue to create two- and three-dimensional surfaces and artworks through patterns of cuts in a wide variety of materials such as textiles, polymer foils, wood, metal and others. These cuts can be made by hand, or cut by machine, using technologies such as laser cutting. Novel technologies and materials open the way for an innovative expansion of the characteristics, functions and the aesthetic value of the textiles and surfaces created through these processes. The in-depth study and calculation of the geometry of such patterns of cuts also plays an important role in the scientific research of “smart” surfaces, as well as of surfaces which have the capability to morph from a two-dimensional structure into a three-dimensional one and vice versa. The current research has as its aim to survey how contemporary designers study and develop cutting techniques in unconventional ways, such as creating three-dimensional structures using minimal manipulation, engineering the properties of surfaces and finding alternative ways of constructing objects. The relation between structure, function and aesthetics and the technologies and materials used will be analysed to determine prevalent tendencies in the field.

Integration of ZnO nanorods with MOS capacitor for self-powered force sensors and nanogenerators

In this work, we present a novel force-sensing device with zinc oxide nanorods (ZnO NRs) integrated with a metal-oxide-semiconductor (MOS) capacitor and encapsulated with Kapton tape. The details of the fabrication process and working principle of the integrated ZnO NRs-MOS capacitor as a force sensor and nanogenerator have been discussed. The fabricated ZnO-MOS device is tested for both the open-circuit and resistor-connected mode. For an input force in the range of 1–32 N, the open-circuit output voltage of the device is measured to be in the range of 60–100 mV for different device configurations. In the resistor-connected mode, the maximum output power of 0.6 pW is obtained with a 1 MΩ external resistor and input force of 8 N. In addition, the influence of different seed layers (Ag and ZnO) and the patterning geometry of the ZnO nanorods on the output voltage of ZnO-MOS device have been investigated by experiments. An equivalent circuit model of the device has been developed to study the influence of the geometry of ZnO NRs and Kapton tape on the ZnO-MOS device voltage output. This study could be an example of integrating piezoelectric nanomaterials on traditional electronic devices and could inspire novel designs and fabrication methods for nanoscale self-powered force sensors and nanogenerators.

Mechanics-aware deformation of yarn pattern geometry

Mechanics-aware deformation of yarn pattern geometry

A mathematical foundation for foundation paper pieceable quilts

Foundation paper piecing is a popular technique for constructing fabric patchwork quilts using printed paper patterns. But, the construction process imposes constraints on the geometry of the pattern and the order in which the fabric pieces are attached to the quilt. Manually designing foundation paper pieceable patterns that meet all of these constraints is challenging. In this work we mathematically formalize the foundation paper piecing process and use this formalization to develop an algorithm that can automatically check if an input pattern geometry is foundation paper pieceable. Our key insight is that we can represent the geometric pattern design using a certain type of dual hypergraph where nodes represent faces and hyperedges represent seams connecting two or more nodes. We show that determining whether the pattern is paper pieceable is equivalent to checking whether this hypergraph is acyclic, and if it is acyclic, we can apply a leaf-plucking algorithm to the hypergraph to generate viable sewing orders for the pattern geometry. We implement this algorithm in a design tool that allows quilt designers to focus on producing the geometric design of their pattern and let the tool handle the tedious task of determining whether the pattern is foundation paper pieceable.

Mechanics-aware deformation of yarn pattern geometry

Triangle mesh-based simulations are able to produce satisfying animations of knitted and woven cloth; however, they lack the rich geometric detail of yarn-level simulations. Naive texturing approaches do not consider yarn-level physics, while full yarn-level simulations may become prohibitively expensive for large garments. We propose a method to animate yarn-level cloth geometry on top of an underlying deforming mesh in a mechanics-aware fashion. Using triangle strains to interpolate precomputed yarn geometry, we are able to reproduce effects such as knit loops tightening under stretching. In combination with precomputed mesh animation or real-time mesh simulation, our method is able to animate yarn-level cloth in real-time at large scales.

The Validation of Various Technological Factors Impact on the Electron Beam Lithography Process

One of the most significant processes in micro- and nanoelectronics technology is Electron Beam Lithography (EBL). This technique maintains a leading role in extremely high-resolution structures fabrication process with micro- and nanometer dimensions down to dozens of nanometers. The EBL is a highly complex process and determining fundamental technological factors that affect the final pattern shape is crucial. One of them is the used lithography system, consisting of a substrate and a polymer layer that affects the electron scattering effects. To obtain the required pattern geometry, it is also necessary to properly select the electron beam parameters for given materials. The aim of this work is to discuss the differences in the exposition process for various accelerating voltage (EHT) values. Additionally, the investigation of geometry features and the impact of the exposure dose and the structure dimensions on the final absorbed energy distribution profile in the resist layer is presented and discussed. Numerical studies, using CASINO software and Monte Carlo method, are presented to compare the energy distribution in the polymer that affects the structure formation in the resist layer.

Aligned Ti3C2Tx MXene for 3D Micropatterning via Additive Manufacturing.

Selective deposition and preferential alignment of two-dimensional (2D) nanoparticles on complex and flexible three-dimensional (3D) substrates can tune material properties and enrich structural versatility for broad applications in wearable health monitoring, soft robotics, and human-machine interfaces. However, achieving precise and scalable control of the morphology of layer-structured nanomaterials is challenging, especially constructing hierarchical architectures consistent from nanoscale alignment to microscale patterning to complex macroscale landscapes. This work demonstrated a scalable and straightforward hybrid 3D printing method for orientational alignment and positional patterning of 2D MXene nanoparticles. This process involved (i) surface topology design via microcontinuous liquid interface production (μCLIP) and (ii) directed assembly of MXene flakes via capillarity-driven direct ink writing (DIW). With well-managed surface patterning geometry and printing ink quality control, the surface microchannels constrained MXene suspensions and leveraged microforces to facilitate preferential alignment of MXene sheets via layer-by-layer additive depositions. The printed devices displayed multifunctional properties, i.e., anisotropic conductivity and piezoresistive sensing with a wide sensing range, high sensitivity, fast response time, and mechanical durability. Our fabrication technique shows enormous potential for rapid, digital, scalable, and low-cost manufacturing of hierarchical structures, especially for micropatterning and aligning 2D nanoparticles not easily accessible through conventional processing methods.

Upside-Down Molding Approach for Geometrical Parameter-Tunable Photonic Perovskite Nanostructures.

Considering that the periodic photonic nanostructures are commonly realized by expensive nanofabrication processes and the tunability of structure parameters is limited and complicated, we demonstrate a solution-processed upside-down molding method to fabricate photonic resonators on perovskites with a pattern geometry controllable to a certain extent. This upside-down approach not only reveals the effect of capillary force during the imprinting but also can control the waveguide layer thickness due to the inversion of the perovskite membranes.