Machine learning assisted multiphysics simulation for electroplating copper in high aspect ratio through silicon via

Selective thermal emitters with a metallic 2D photonic crystal structure, such as shown in Fig. 1a), have been demonstrated to control the thermal emission spectrum of selective emitters for thermophotovoltaic applications. Traditionally, tungsten has been the metal of choice for thermal emitters due to their natural thermal emission selectivity to wavelengths > 2μm and high melting temperatures. However, due to the unweldable nature of tungsten, system integration of tungsten is difficult. As a result, weldable tantalum nanophotonic cavities have been demonstrated as effective thermal emitters with long wavelength emissivity below that of tungsten, allowing for improved selectivity performance compared to tungsten. However, the aspect ratios (AR) of the tantalum cavities have been demonstrated with a depth to radius aspect ratio of 11.2. The high aspect ratios in relation to tungsten (AR = 2.9) are due to the smaller material absorption at optical wavelengths around 2 μm, which causes Q <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">abs</sub> per unit length to be reduced thus affecting the Q matching condition. The aspect ratio is determined based on Q-matching, where the radiative Q (Q <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rad</sub> ) and absorption Q (Q <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">abs</sub> ) of the cavity must be equal for maximum absorption. The high cavity aspect ratio significantly hinders the fabrication methods available to manufacture the tantalum devices. For example, because of the high aspect ratio cavities, low-cost and scalable fabrication methods such as surface deposition of tantalum via sputtering or evaporation are not possible due to poor step coverage. Thus, previous methods used expensive and difficult to prepare 2" diameter tantalum wafers with custom etching methods. Accordingly, low aspect ratio cavities are key for a low-cost and scalable deployment of thermophotovoltaic devices.

Free-standing nanofins or pillar meta-atoms are the most common constituent building blocks in metalenses and metasurfaces in general. Here, we present an alternative metasurface geometry based on high aspect ratio via-holes. We design and characterize metalenses comprising ultradeep via-holes in 5 μm thick free-standing silicon membranes with hole aspect ratios approaching 30:1. These metalenses focus incident infrared light into a diffraction-limited spot. Instead of shaping the metasurface optical phase profile alone, we engineer both transmitted phase and amplitude profiles simultaneously by inverse-designing the lens effective index profile. This approach improves the impedance match between the incident and transmitted waves, thereby increasing the focusing efficiency. The holey platform increases the accessible aspect ratio of optical nanostructures without sacrificing mechanical robustness. The high nanostructure aspect ratio also increases the chromatic group delay range attainable, paving the way for a generation of high aspect ratio ruggedized flat optics, including large-area broadband achromatic metalenses.

Influence of platelet aspect ratio on the mechanical behaviour of bio-inspired nanocomposites using molecular dynamics

“Clickable” nanowires with well-defined and uniform structures made of conjugated polyfluorene polymers were successfully fabricated by single particle nanofabrication technique (SPNT). Poly[(9,9-dihex-5-yn-1-ylfluorenyl-2,7-diyl)-co-(9,9′-di-n-octylfluorenyl-2,7-diyl)] (F6E8) and poly[(9,9-dihex-5-yn-1-ylfluorenyl-2,7-diyl)-co-(2,2′-bithiophene)] (F6E2T) underwent an efficient cross-linking reaction upon irradiation, resulting in formation of one-dimensional nanostructures with high and desired aspect ratio reaching up to 200. Alkyne groups on the surface of nanowires were functionalized effectively by click reaction with fluorescent 5-TAMRA-PEG3-azide, which was confirmed by confocal microscopy. Substrates functionalized with the nanowires provide dramatic expansion of “clickable” surface area immobilized directly with TAMRA, and the fluorescence resonance energy transfer (FRET) processes between TAMRA and nanowire backbones are demonstrated as biological sensing platforms.

Graphene nanoclusters embedded nickel cobaltite nanofibers as multifunctional electrocatalyst for glucose sensing and water-splitting applications

Glass fiber (GF)‐related mold abrasion and tool wear make it undesirable for certain thermoplastics applications. Furthermore, fiber attrition during processing and orientation sensitivity raise concerns over compromised performance. In this study, kaolin minerals with varying properties and surface‐treatments are tested to potentially replace GFs in nylon composites. Composites are melt‐compounded and injection molded using lab‐scale and industrial‐scale equipment. Mechanical properties (tensile, flex, impact), heat distortion temperature, and thermal decomposition using thermogravimetric analysis (TGA) are used to comparatively characterize kaolin composite formulations against 30% weight GF composites. Kaolin minerals with high aspect ratio and good interfacial contact are found to show strength and modulus improvements up to 80% that of GF. Additionally, low aspect ratio kaolin composites were found to surpass GF composites in impact strength. A synergistic effect is found between high and low aspect ratio kaolin that can potentially lead to further enhancement in properties with the added possibility of blending minerals to customize composite performance. Such findings suggest that kaolin minerals can be used to customize the properties of composites in manners previously unattainable through GF usage alone. Scale up trials show potential for kaolin to replace GFs at industrial levels. POLYM. ENG. SCI., 59:E330–E338, 2019. © 2018 Society of Plastics Engineers

Microholes, especially high aspect ratio, high-quality microholes with small diameters (<100 μm), have broad applications. However, it is very difficult for traditional drilling methods to obtain deep microholes, especially with aspect ratios of over 50:1. Femtosecond lasers provide a promising solution for efficient drilling of deep microholes with high-precision material removal, reduced recast/microcracks, minimized heat-affected zones, and the absence of plasma-shielding effects. In this work, a comparison study of high aspect ratio, high-quality microholes fabricated in a poly(methyl methacrylate) (PMMA) bulk substrate with the ambient pressure adjusted from 105 Pa (air) down to 1 Pa (vacuum) is presented. High aspect ratio (over 100:1) microholes were obtained in a vacuum environment. The contrast between microhole evolution in air and in vacuum was investigated. The results indicate that efficient energy propagation and easy ejection of ablated material/plasma are probably the most important benefits of drilling microholes in vacuum. The dependence of microhole shapes on different fabrication parameters, including pulse energy and ambient pressure, was investigated to quantitatively reveal the underlying mechanisms. The enhanced drilling effect in vacuum was only found in a high pulse energy region (E p > 20 μJ), and it becomes saturated when the ambient pressure was reduced to ~102 Pa at a pulse energy of 50 μJ. Drilling microholes in a vacuum provides a simple and effective way of rapidly fabricating high aspect ratio, high-quality microholes.

Anodic porous alumina templates with controlled microscale geometrical structures were prepared by a process combining mask formation and subsequent selective etching of the alumina layer. In this process, the anisotropic etching of anodic porous alumina allows the preparation of anodic porous alumina with microhole array patterns having high aspect ratios. The electrodeposition of Ni using the obtained alumina templates generated an array of Ni micropillars with high aspect ratios. The height of Ni micropillars could also be controlled by adjusting the thickness of the anodic porous alumina. The obtained Ni micropillar array with a high aspect ratio was applied as a mold for imprinting. The ordered microstructures of TiO2 with high aspect ratios were prepared by imprinting using the Ni mold.

ABSTRACTPolymer nanocomposites consisting of electrically conductive nanofillers with high aspect ratios are widely utilized for high‐performance applications such as sensors and electronics. Silver nanowires (AgNWs) synthesized through polyol reduction have been reported to show excellent electrical conductivity, hydrophilicity, and high aspect ratios. In this study, the influence of the aspect ratios of the AgNWs on the rheological and electrical properties of the fabricated polystyrene (PS)/AgNW nanocomposites was chiefly investigated. The nanocomposites were made by combining a dispersion of AgNWs with a suspension of PS particles, followed by freeze‐drying the PS/AgNW mixture harnessing the latex technology. Scanning electron microscopy, UV–Vis spectroscopy, and thermogravimetric analysis were performed on the nanocomposites to investigate the morphological, optical, and thermal properties, respectively; in addition, X‐ray photoelectron spectroscopy was performed to examine the hydrophilic polymer poly(vinylpyrrolidone)‐capped AgNW surfaces. The rheological behavior of the nanocomposites changed from liquid‐like to solid‐like after the addition of AgNWs with high aspect ratios. The electrical percolation threshold of the AgNWs in the nanocomposites was determined by the aspect ratio of the nanofiller rather than by its length. Thus, the various properties of the PS/AgNW nanocomposites could be tuned by tailoring the aspect ratios of the AgNWs. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47927.

With rapid development in micromachining, high aspect ratio (AR > 10) micro-holes are essentially required in applications such as spinneret holes, biomedical needles, fuel injectors, cooling channels, etc. Machining such high aspect ratio micro holes on superalloys are challenging for micromachining processes. A high aspect ratio micro hole can be machined via. Micro Electrical Discharge Machining (MEDM) process with optimum levels of operating parameters. Work reported in this paper is aimed to investigate the effect of machining parameters of MEDM to produc micro-holes in Hastelloy C276. Extensive experimentations based on Taguchi Designs of Experiments (DOE) were conducted to identify the most influential processing parameters while machining micro holes of more than 10 aspect ratios. The experimental results are discussed which quantify an individual and combined effect of different operating parameters on the overall performance of MEDM like material removal rate (MRR) and tool wear rate (TWR). It is found that capacitance and spindle rotation speed are the most important parameters controlling the stability of the process. A direct relation of TWR has been found with discharge energy (capacitance and voltage). At optimum process parameter conditions, the aspect ratio (depth/diameter) of 12.5 is achieved while machining holes with 400 µm diameter.

The aim of this work is to study and compare the morphology and rheology of cellulose nanofibrils (CNFs) from bleached softwood kraft pulp by several mechanical treatment methods. Three different kinds of CNFs were prepared in this work: (i) ones produced by PFI milling and microfluidic homogenization (RM-CNFs), (ii) ones produced by grinding and microfluidic homogenization (GM-CNFs), and (iii) ones produced by ball milling and ultrasonication (BU-CNFs). RM-CNFs had a high aspect ratio and the highest viscosity, storage modulus, and loss modulus. GM-CNFs had homogeneous size distributions, but low aspect ratio due to severe shearing of narrower orifice of chamber in microfluidic homogenization process. For BU-CNFs, the size distributions were heterogeneous, but they had a high aspect ratio. The three kinds of CNFs all had a lower crystallinity index than BSKP, and the degree of polymerization decreased with the increase of treatment intensity. Results of rheology measurements showed that those CNFs had a high degree of fibrillation and had a wider linear viscoelastic region in oscillatory strain measurements. Also the CNFs with high aspect ratio had a high viscosity and modulus. Additional treatments did not always increase the viscosity and modulus due to too severe treatments, which could cause the decrease of aspect ratio of CNFs. The RM-CNFs had a high viscosity and modulus, which means they are suitable in applications of rheology control.

The typical thin-film photovoltaic cells incorporate a textured transparent conductive oxide film to efficiently harvest solar energy [1]. It is well known that the light trapping performance provided by the random texturing has largely fallen short as compared to the initial expectations based on the performance achieved from similar features in thick wafer based cells [1-3]. Several reasons have been accounted for this including interference and coherent effects, smaller photonic density of states in thin film layers, and inability to construct Lambertian scattering surfaces with small textures [1-3]. Coherent periodic structures that can better confine the incident solar energy in the volume occupied by the efficient photoactive materials have been proposed [2,3]. Several research groups have concluded that the high aspect ratio structures such as a periodic array of very thin but tall pillars or cones will be needed for high performance cells. Similarly, high aspect ration holes have also been proposed [2,3]. In this work we performed rigorous opto-electronic analysis of several different device configurations for the next generation high aspect ratio periodic thin film photovoltaic cells. Each device configuration is exhaustively optimized for all geometrical variables to achieve maximum short circuit current under 1SUN AM1.5g radiation. This enables us to objectively compare the potential of different proposed cell designs. We show results from our studies of high aspect ratio pillars versus high aspect ratio perforations (holes); constant cross-section cylindrical pillars versus tapered cross-section conical pillars; square cross-section versus circular cross-section pillars and holes and square periodic lattice versus hexagonal periodic lattice. We also studied differences between the cases when a-Si p-i-n stack is conformally deposited on the high aspect ratio periodic features and when a thick layer of TCO is used to planarize the features before a p-i-n stack is grown. Results will be shown for both the substrate and superstrate configuration of devices. We developed a fully rigorous and coherent opto-electronic simulation platform that is used for this work. In the past we developed a Fourier domain based rigorous coherent optical simulator REMS that was used for studying the random textured devices. We showed that this simulator predicted both the optical scattering properties such as spectral haze and reflectivity of textured TCO surfaces as well as the QE of single junction and tandem junction devices grown on these surfaces with very good accuracy [1-3]. In the present work we extend this simulation capability to analyze and optimize next generation patterned periodic solar cells. In addition to the optical light trapping, these high aspect ratio structures may greatly alter the charge carriers transport pattern and collection efficiency. In a p-i-n stack conformally deposited on a columnar structure, the charge carriers are expected to be collected in the direction perpendicular to the axis of the columns while photons are expected to be absorbed while waveguiding in the direction parallel to the axis. Hence, it is very important to rigorously study the charge carrier dynamics coupled with a full 3D Maxwell solver. Here, we integrated the very fast REMS 3D Maxwell solver with the established device simulator Sentaurus™ from Synpsys <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</sup> Inc. REMS is Fourier domain based method and is very fast compared to the FDTD or FEM based methods. This allows us to exhaustively optimize the several geometrical features of the device configuration in reasonable amount of time [1-3].

We present a new formation technology for a plasma display panel (PDP) barrier-rib structure by which we can obtain a barrier-rib with a high aspect ratio and reduce the manufacturing cost. Firstly, a precise metal mould is manufactured for massively replicating the PDP barrier-rib construction using the UV-LIGA process with a thick negative photoresist (SU-8 50: Microchem Corp). The proposed sequence includes several processes: amorphous silicon as an adhesion layer; dipping into xylene and n-butyl acetate after the development of SU-8; two step removal of the SU-8 layer; rip-off process, etc. The proposed processes produce a copper mould with a high aspect ratio, good surface roughness and a uniform thickness. Secondly, a PDP barrier-rib structure is formed using the roll-pressing method with a reusable metal mould fabricated by the proposed UV-LIGA process. This is a very simple and inexpensive method consisting of printing the barrier-rib paste, drying, roll-pressing and firing. Consequently, by combining the UV-LIGA and roll-pressing processes, the desired barrier-rib shapes can be made with a high aspect ratio and various dimensions. The combination of the UV-LIGA and roll-pressing processes also demonstrates the possibility of achieving two major goals in the barrier-rib processes; i.e., developing a barrier-rib structure with a high aspect ratio that can be applied to high-definition televisions, and reducing the manufacturing cost.

This paper was presented at the Fourth International Workshop on High Aspect Ratio Micro-Structure Technology (HARMST) 2001 in Baden-Baden, Germany. For building high aspect ratio parts, using a combination of UV lithography and electroplating is a very promising approach. This paper describes investigations regarding the application of UV lithography and electroplating to fabricate high aspect ratio component parts of microactuators, such as coils and pole pieces. As resist materials, both novolac-based resists and photosensitive epoxy were investigated. The high aspect ratio photomasks were used as micromolds for electroplating coils and magnetic structures in micromotors.

A specially designed and developed spherical coupling fiber probe was proposed to improve the dimensional measurement accuracy of microstructures with high aspect ratio. The effectiveness of the proposed probe was verified through simulation and experiment. Our simulation results indicated that the maximum deformation was less than 40 µm during the measurement and, therefore, the shaft of the proposed probe did not touch the sidewall of a micro hole. Our experimental results indicated that a static centroid stability of 1.76 µm could be achieved with a resolution of 30 nm in directions X and Y, which meant that the special light path arrangement of the proposed probe overcame the shadowing effect and improved the dimensional measurement accuracy of microstructures with high aspect ratio. It was, therefore, concluded that the proposed probe was suitable for the dimensional measurement of microstructures with a high aspect ratio.