A High Aspect Ratio Inverse-Designed Holey Metalens.

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.

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

We report herein the growth Titanium Dioxide (TiO2) nanorods on FTO substrate with different aspect ratio. It is observed that the photo anodic behaviour is highly influenced by the aspect ratio of as -grown TiO2 nanorods. Hydrolysis of TiCl4 leads to the formation of TiO2 nanorods on FTO substrate. Nanorods of different aspect ratio are obtained by varying the concentration (0.1M, 0.2M) of TiCl4. The XRD pattern confirms the formation of rutile, tetragonal TiO2 nanorods with high crystallinity. From the FESEM images, the length and width of the nanorods are observed. The aspect ratio is found to be 151 for low concentration TiO2 nanorod array (TR1) and 330 for high concentration TiO2 nanorod array (TR2). The specific surface area, porosity of the samples was calculated using Brunauer–Emmett–Teller (BET) analysis. Superior surface properties are noticed in the case of TiO2 nanorods with high aspect ratio. The photovoltaic activity of TiO2 nanorods with high aspect ratio is found to be relatively high as compared to those with low aspect ratio.

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.

“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

A method was devised for estimating aspect ratio, wing ratio, wing area, wing loading, and wing length from study skins of bats. These measures were taken of 136 species representing 15 families. Wing area and loading are positively, and wing length negatively, correlated with size. Aspect and tip ratios are independent of size and of each other. Distinctive combinations of some of these variables characterize groups of bats that presumably have similar flight modes. Speed is positively correlated with aspect ratio and tip index, but regresses significantly only on the former. Long tips coupled with low aspect ratio may characterize hoverers. Long wings and short tips may characterize bats that are capable of remaining airborne at slow speeds. Most bats with low aspect ratios are forest dwellers, whereas species with high aspect ratios are migrants and foragers in open areas.

I ntroduction. High aspect ratio (AR) processes are widely used in front end of line (FEOL) IC manufacturing. Figure 1 depicts high (AR) trench cleaning process. Polymerization residues produced during the dry etch process will cause many problems such as STI voids in the follow-up process if the residues are not removed. This can lead to lower yield and reduction of chip life[1]. It is difficult to completely clean the residue inside trench with aspect ratio greater than 10.As shown in Figure.2, poor wetting of the liquid in the high AR trench, prevents the cleaning of the whole trench. Typically, the wafer surface can be easily cleaned, however residues remain inside of the trench. The cleaning of polymerization residues inside the trench and eliminating watermarks are the main issues in high (AR) cleaning processes. In this paper, we design an infiltration experiment, polymerization residues cleaning experiment and drying experiment to verify single wafer RCA clean performance on high (AR) trench processes. The verification of the single wafer RCA wafer clean is through yield data. Experimental. In the infiltration experiment, a layer of 500A SiO2 was grown on the high aspect ratios trench wafer. As shown in Table I, This was followed by treating the wafers with different process conditions on ACM single wafer tool. The remaining oxide thickness inside trench was measured by transmission electron microscope (TEM). Figure 3 shows experimental steps.In the polymerization residue cleaning experiment, 7 wafers with trenches after dry etching were treated with different chemical and process mode shown in Table II on ACM single wafer tool. The defect count was measured by the inline defect detection equipment and the scanning electron microscope.(SEM)In the drying experiment, high AR wafers were processed on an ACM single wafer tool, under different drying conditions. The trench wafer were then transferred into a vacuum bag and the air was evacuated. If there is no watermark on wafer surface within 15 minutes, we consider that the wafer has been dried in the macro level.Wafers were split between being cleaned by single wafer RCA clean and by bench RCA clean. The wafers are scanned for defect count on the wafer surface after the cleaning process for both the base line (bench) and the single wafer tool. Finally, we review yield on device completion to check results of single wafer and bench clean. Results. Table I shows the result of dHF infiltration experiment. When the pre rinse DIW time exceeds 30 seconds, the whole trench is soaked by DIW, allowing the dHF to permeate the whole trench, with oxide loss being similar from the top to the bottom of the trench.Table II shows the result of cleaning experiment. ACM Single wafer dHF+SC1 (mega) process can effectively clean the whole trench. Figure 4 and 5 shows defect map and SEM picture after single DHF+SC1(mega).Figure 6 shows the effect of chuck rotation speed and N2 flow rate on wafer drying. Figure 10 shows particle performance under different drying process conditions. Figure 7 shows the inline defect map and SEM after dry process.Figure 8 & 9 show the particle performance after the clean process. No special particle map appears with the single wafer clean process. Fig 10 shows the yield performance after all of the processes are completed. Average yield of single clean process is better than the baseline bench clean process. Table 3 shows detailed yield data from the wafer splits . Conclusion. Infiltration and cleaning experiment result shows that single wafer RCA clean can effectively clean the polymerization residues inside of high aspect ratio trenches. Dry experiment result shows that single wafer process can reduce watermark and particles in the dry step. Inline particle performance and final yield performance shows that single wafer RCA clean is better than baseline bench. Single wafer clean has lower standard deviation than bench clean and SW RCA clean in high (AR) trench process is feasible and effective. References. Xue. Research on High Aspect Ratio TSV Cleaning Technology enhanced by Megasonic[D]. Beijing: University of Chinese Academy of Sciences, 2016.JiHoon Cha, ChangSup Mun, etal. Low Si recess on cleaning process by dilute HF/SC-1 with megasonic[J]. Solid State Phenomena, 2008, 134:209-212.H Wang, Yue Ma, Fuping.Chen, etal. Removal of Fine Particle using SAPS Technology and Functional Water[J]. Solid State Phenomena, 2013, 195:185-190.Dae-Hong EOM, Geun-Bae LIM, etal. Reaction of Ozone and H2O2 in NH4OH Solutionsand Their Reaction with Silicon Wafers[J]. Japanese Journal of Applied Physics, 2004, 43:3335-3339. Figure 1

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.

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.

Faceted ZnO nanorods with different aspect ratios were synthesized by a solvothermal method by tuning the reaction time. Increased reaction leads to the formation of high aspect ratio ZnO nanorods largely bound by the prism planes. The high aspect ratio rods showed significantly higher visible light photocatalytic activity when compared to the lower aspect ratio structures. It is proposed that the higher activity is due to better charge separation in the elongated 1D structure. In addition, the fraction of unsaturated Zn(2+) sites is higher on the {1010} facets, leading to better adsorption of oxygen-containing species. These species enhance the production of reactive radicals that are responsible for photodegradation. The photocurrent for these ZnO nanostructures under solar light was measured and a direct correlation between photocurrent and aspect ratio was observed. Since the underlying mechanisms for photodegradation and photocurrent generation are directly related to the efficiency of electron-hole creation and separation, this observation corroborates that the charge separation processes are indeed enhanced in the high aspect ratio structures. The efficiency of photoconduction (electron-hole pair separation) could be further improved by attaching Au nanoparticles on ZnO, which can act as a sink for the electrons. This heterostructure exhibits a high chemisorption of oxygen, which facilitates the production of highly reactive radicals contributing to the high photoreactivity. The suggested mechanisms are applicable to other n-type semiconductor nanostructures with important implications for applications relating to energy and the environment.

3D integration is an emerging semiconductor technology that is used to form highly integrated small-factor electronic systems by vertically stacking two or more thin electronic chips in a single package. In metallization of 3D through-substrate vias (TSuV) such as through-silicon (TSV), through-glass (TGV), through-ceramic (TCV) interconnects et al, TSuV having a very small diameter (down to several microns) and long length (hundreds of microns) are filled with plated metal in order to create massive networks of uniform interconnects with high aspect ratio (length/diameter) > 20. Existing conventional industry processes are based on expensive physical-vapor-deposition (PVD) technology, which has serious limitations on via fill uniformity and metal quality (poor step coverage, voids and other defects) as well as is limited to aspect ratios < 10.Electrochemical deposition processes have been extensively studied for 3D interconnects. These processes are appealing due to superior performance as compared to conventional PVD processes at a substantially lower cost. NANO3D’s processes are based on novel electrochemical nanomaterials (plating solutions with self-assembled suppression-based organic additives to achieve bottom up fill and conformal electroless nickel alloys/copper barrier/seed) that provide defect-free TSuV fill with Cu or other metals for aspect ratios up to >20 [1-5]. Electrochemical deposition techniques have no limitations on chips design rules (down below 20 nm) and can be applied to all types of 3D applications from logic and memory to MEMS, wireless and power electronics. Electrochemical TSuV metallization is fully compatible with all process steps in various 3D TSuV manufacturing schemes currently under evaluation and can be easily incorporated into any finally standardized “process flow of reference”. The low cost electrochemical TSuV technology addresses the major threats for adoption of 3D TSuV that is the scalability to high aspect ratio and the cost. Another threat for adoption of 3D TSuV technology, that is related to power density limitation and thermal dissipation from thinned dies are expected to be solved by controlled expansion metal alloys (INVAR et al.) where electrochemical deposition offers high flexibility for designers with various aspect ratios and via sizes.In this work, copper and INVAR electroplating as well as nickel alloys and copper electroless deposition processes have been developed and characterized to achieve bottom up fill in trenches & vias of high aspect ratio and wide range of features sizes with superior interconnect properties including low electrical resistivity, CTE and internal stress. Plated films with low-thermal expansion (of about 0.4±0.1 (x10-6, (K-1)) and ultralow internal stress (of about 30 MPa) have been deposited on patterned substrates such as TSuV on various substrates, redistribution layers (RDL), pillars and bumps for 3D Interconnects. The plated patterned substrates are flat, smooth, uniform, defect free and possess with complete fill of TSuV and well controlled thickness non-uniformity of about 5 % @ 3 σ for Cu & INVAR & Ni alloys films (Figure). Thermal shock testing of plated TSuV substrates showed promising reliability & adhesion results after 500 cycles of thermal shock with no cracking and delamination. References V.M. Dubin, A.L. Gindilis, B.L. Walton, K. Norelli, A.U. Liyanage, S.R. Bauers and D.C. Johnson. ECS Transactions, 2017, 75 (34), 27.S. Taushanoff and V. M. Dubin. ECS Transactions, 2017, 77 (11), 877.V.M. Dubin, K. Norelli, and P.N. Plassmeyer. ECS Transactions, 2017, 77 (11), 887.V.M. Dubin, M.O. Lisunova, and B.L. Walton. Journal of The Electrochemical Society, 2017, 164, D321.S. Taushanoff, V.M. Dubin, A. Wallace and H. A. Mantooth. ECS Transactions, 2018, 85 (13) 803. Figure 1

Influences of the sample shape and compression temperature on the deformation behavior and mechanical properties of human dentin