Inter-hole Distance Research Articles

Preparation of Ordered Nanohole Arrays with High Aspect Ratios by Anodization of Prepatterned 304 Stainless Steel

A nanohole array structure with a regular array of cylindrical holes of a high aspect ratio with a period of 63 nm can be obtained by anodizing 304 stainless steel with a concave pattern. It was shown that matching the concave period to the anodization voltage is important to achieving the fabrication of nanohole arrays with a high aspect ratio. This is because the interhole distance of anodic porous oxide obtained by the anodization of 304 stainless steel in ethylene glycol containing 0.1 M ammonium fluoride depends on the anodization voltage. By optimizing the fabrication conditions, it was possible to fabricate highly ordered nanohole arrays with aspect ratios exceeding 100. The nanohole arrays obtained in this study are promising as key materials for fabricating various functional devices.

Efficient fabrication of ordered alumina through-hole membranes using a TiO2 protective layer prepared by atomic layer deposition.

Ordered alumina through-hole membranes were obtained by a combination of the anodization of Al, formation of a TiO2 protective layer, and subsequent etching. Two-layered anodic porous alumina materials composed of TiO2-coated and noncoated alumina were prepared by the combination of the anodization of Al and the formation of a TiO2 protective layer by atomic layer deposition (ALD). The obtained two layers of anodic porous alumina have different solubilities because the TiO2 thin layer formed by ALD acts as a protective layer that prevents the dissolution of the alumina layer during wet etching of the sample in an etchant. After the selective dissolution of the bottom layer of porous alumina without the TiO2 layer, an ordered alumina through-hole membrane could be detached from the Al substrate. This process allows the repeated preparation of ordered alumina through-hole membranes from a single Al substrate. By this process, ordered alumina through-hole membranes with large interhole distances could also be obtained. The obtained alumina through-hole membrane can be used in various applications.

Influence of hybrid pin profile on microstructural and mechanical properties of Al/SiC graded composites produced by friction stir processing

Friction stir processing (FSP) was employed to fabricate a surface graded composite by embedding SiC reinforcement particles in an AA6082-T6 matrix. Conical blind holes were drilled on the surface of the plate with varying inter-hole distances. The processing was performed with the different number of passes by keeping rotational and traverse speed constant. A new hybrid tool with a combination of conventional conical threaded tool and the triangular cross-sectioned tool was used in processing. The microstructural features of the processed samples were examined by a 3D microscope and scanning electron microscope (SEM). Mechanical properties such as microhardness, tensile strength was thoroughly evaluated. It is reported that the number of passes played an essential role in the distribution of reinforcement particles and grain refinement. The hardness value improved by applying multiple passes. The fractured tensile samples showed ductile failure. The sample treated with double passes gave better results with the homogenous distribution of reinforcement particles compared to samples processed with a single pass.

Kinetic Monte Carlo simulation of the growth of In nanostructures by droplet epitaxy on AlGaAs nanopatterned surfaces

In this paper, the results of the simulation of the In/AlGaAs growth on nanopatterned surfaces using modified analytical–Monte Carlo model are presented. The surface density of nanostructures is demonstrated to slightly decrease with increasing Al content. A decrease of an interhole distance leads to the occupation of a small part of a hole which can be prevented by a decrease of the hole volume. The best localization of In nanostructures on AlGaAs surfaces nanopatterned with holes at a distance of more than 125 nm can be achieved at a temperature of 300°C or higher. A decrease in temperature requires a sufficient decrease of an interhole distance to avoid nucleation beyond predefined positions.

Field localization of hexagonal and short-range ordered plasmonic nanoholes investigated by cathodoluminescence

Plasmonic nanoholes have attracted significant attention among nanoplasmonic devices, especially as biosensing platforms, where nanohole arrays can efficiently enhance and confine the electromagnetic field through surface plasmon polaritons, providing a sensitive detection. In nanohole arrays, the optical resonances are typically determined by the inter-hole distance or periodicity with respect to the surface plasmon wavelength. However, for short-range ordered (SRO) arrays, the inter-hole distance varies locally, so the plasmon resonance changes. In this study, we investigate the local resonance of SRO nanoholes using a cathodoluminescence technique and compare it with hexagonally ordered nanoholes. The cathodoluminescence photon maps and resonance peak analysis reveal that the electric fields are confined at the edges of holes and that their resonances are determined by inter-hole distances as well as by their distributions. This demonstrates the Anderson localization of the electromagnetic waves showing locally enhanced electromagnetic local density of states in SRO nanoholes.

Analytical–Monte Carlo model of the growth of In nanostructures during droplet epitaxy on the triangle-patterned GaAs substrates

Kinetic Monte Carlo simulations combined with the analytical nucleation theory are used to study droplet epitaxy of indium on the GaAs substrates patterned with triangular-shaped nanoholes. The simulation results demonstrate that the growth on the Ga-stabilized surface provides much better selectivity than the formation of nanostructures on the As-stabilized surface because of the stronger bonding with As atoms of the substrate. We estimate technological parameters which allow obtaining required characteristics of nanostructures with precise positioning and complete filling of holes. The distance between nanostructures is considered to be controlled by the growth temperature at an appropriate interhole distance. At the same time, dimensions of nanostructures are outlined by the geometrical parameters of holes and can be adjusted by the deposition thickness.

Constructing sensitive SERS substrate with a sandwich structure separated by single layer graphene

We report a sandwich-structured surface-enhanced Raman scattering substrate by integrating gold nanoparticles and electron beam lithography-fabricated hexagon-shaped silver nanohole arrays separated by single layer graphene. In the sandwich configuration, the graphene interlayer plays multiple roles for promoting the surface-enhanced Raman scattering performances: (i) acting as a supporting layer to avoid the dropping of the top layer of gold nanoparticles; (ii) an intrinsic spacer to create nanometer-scale gaps between gold nanoparticles and hexagon-shaped silver nanohole arrays; (iii) serving as a protective layer to suppress the oxidation of the bottom metal silver; (iv) functioning as a molecule harvester for adsorbing the target analyte. By decreasing inter-hole distances of hexagon-shaped silver nanohole arrays, we have obtained sub-10 nm-wide gaps neighboring the adjacent silver holes. Finite element numerical simulations demonstrated that the gold nanoparticle-graphene-hexagon-shaped silver nanohole array hybrid system generates a substantial amount of hot spots with strong electric field enhancement. The well-designed and fabricated gold nanoparticle-monolayer graphene-hexagon-shaped silver nanohole array sandwich structure exhibits high sensitivity with the limit of detection at sub-picomolar level and good reproducibility with a standard deviation of 6.2% for crystal violet. The work endows great potentials to the rational design and fabrication of two-dimensional material-plasmonic hybrids for surface-enhanced Raman scattering applications.

Anti-cell adhesion characteristics of nanotextured surface for implantable biomedical device

In this study, anti-cell adhesion characteristics of a nanotextured polymer surface prepared by a nano-imprint process were investigated by culturing NIH 3T3 fibroblast cells on the surface. The nanotextured surface, made of biocompatible polymer, was covered by nanodimples having a diameter of 220± 5 nm and inter-hole distance of 320 ± 5 nm. Migration of NIH 3T3 cells was confined within a small area, and cell aggregation was observed on the nanotextured surface. Aggregated cells were fully viable. On the other hand, NIH 3T3 cells cultured on a smooth surface actively migrated and eventually covered the entire surface area after 56 hours. Because the nanotextured surface displayed anti-cell adhesion characteristics without causing apoptosis, it can be used in implantable biomedical devices to confer anti-cell adhesion properties without any chemical treatment.

Magnetic hardening and domain structure in Co/Pt antidots with perpendicular anisotropy

(Co(0.4 nm)/Pt(0.7 nm))x (x = 10, 20, 30) multilayer antidot thin films (films with arrays of nanoholes) have been grown by dc sputtering onto self-assembled pores of anodic alumina membranes with a tailored diameter and a fixed inter-hole distance. The magnetic behavior has been quantified by vibrating sample magnetometry, and the surface magnetization patterns have been imaged by magnetic force microscopy. The magnetization reversal mechanism is characterized by two steps depending on the film thickness and antidot diameter. These steps are ascribed to the nucleation and demagnetization of magnetic stripe domains. Their presence confirms the perpendicular anisotropy of the multilayer antidot films. The coercivity of antidot thin film is larger than that of the continuous films due to additional pinning centers provided by antidots. The width of the stripe domains increases as a function of film thickness. The demagnetization is further investigated through micromagnetic simulations that are in agreement with the measured hysteresis loops and their features. Different reversal mechanisms and an increase of the domain width in antidot thin films are also confirmed as a function of the magnetic anisotropy, antidot diameter and thickness of the thin film. The presence of antidots with a designed geometry is revealed to be successful in tailoring the coercivity of the thin films and magnetic patterns, which is relevant for advances in nanoscale technologies.

Investigation of Flow Aerodynamics for Optimal Fuel Placement and Mixing in the Radial Swirler Slot of a Dry Low Emission Gas Turbine Combustion Chamber

This paper is concerned with optimizing the fuel–air mixing processes that take place within the radial swirler slot of a dry low emission (DLE) combustion system. The aerodynamics of the flow within the slot is complex and this, together with the placement of the fuel holes with cross injection, controls the mixing of the fuel and air. Computational fluid dynamics (CFD) with the shear stress transport (SST) (k–ω) turbulence model was used for flow and mixing predictions within the radial swirler slot and for conducting a CFD-based design of experiments (DOE) optimization study, in which different parameters related to the fuel injection holes were varied. The optimization study was comprised of 25 orthogonal design configurations in the Taguchi L25 orthogonal array (OA). The test domain for the CFD, and its experimental validation, was a large-scale representation of a swirler slot from the Siemens proprietary DLE combustion system. The DOE study showed that the number of fuel holes, injection hole diameter, and interhole distance are the most influential parameters for determining optimal fuel mixing. Consequently, the optimized mixing configuration obtained from the above study was experimentally tested on an atmospheric test facility. The mixing patterns from experiments at various axial locations across the slot are in good agreement with the mixing predictions from the optimal CFD model. The optimized fuel injection design improved mixing compared with the baseline design by about 60%.

Dual-Microstructured Porous, Anisotropic Film for Biomimicking of Endothelial Basement Membrane.

Human endothelial basement membrane (BM) plays a pivotal role in vascular development and homeostasis. Here, a bioresponsive film with dual-microstructured geometries was engineered to mimic the structural roles of the endothelial BM in developing vessels, for vascular tissue engineering (TE) application. Flexible poly(ε-caprolactone) (PCL) thin film was fabricated with microscale anisotropic ridges/grooves and through-holes using a combination of uniaxial thermal stretching and direct laser perforation, respectively. Through optimizing the interhole distance, human mesenchymal stem cells (MSCs) cultured on the PCL film's ridges/grooves obtained an intact cell alignment efficiency. With prolonged culturing for 8 days, these cells formed aligned cell multilayers as found in native tunica media. By coculturing human umbilical vein endothelial cells (HUVECs) on the opposite side of the film, HUVECs were observed to build up transmural interdigitation cell-cell contact with MSCs via the through-holes, leading to a rapid endothelialization on the PCL film surface. Furthermore, vascular tissue construction based on the PCL film showed enhanced bioactivity with an elevated total nitric oxide level as compared to single MSCs or HUVECs culturing and indirect MSCs/HUVECs coculturing systems. These results suggested that the dual-microstructured porous and anisotropic film could simulate the structural roles of endothelial BM for vascular reconstruction, with aligned stromal cell multilayers, rapid endothelialization, and direct cell-cell interaction between the engineered stromal and endothelial components. This study has implications of recapitulating endothelial BM architecture for the de novo design of vascular TE scaffolds.

An experimental and numerical investigation of heat transfer distribution of perforated plate burner flames impinging on a flat plate

Heat transfer from perforated plate burner flame impinging on a flat plate finds importance in industrial (gas fired boiler) and domestic heating (household gas burner and commercial hotel gas burners) applications. A limited study on heat transfer distribution of this kind of burner plate is found in the literature. In the present work, high resolution heat flux is estimated by the inverse heat conduction (IHCP) technique based on use of analytical solution for semi-infinite medium for the impingement plate. Inline, star and staggered holes patterns with three different inter-hole distances (pitch) are considered in the present study. Methane–air premixed flame of Reynolds number varying from 50 to 600 and an equivalence ratio varying from 0.6 to 1.2 is considered. The hole to impingement plate distance is varied from 3 to 7. From the experimental results, it is found that the inline and staggered patterns have the same heat flux averaged over an area of 50 mm × 50 mm for different Reynolds number. The intermediate pitch of 7 mm is the optimal pitch over the entire mixture flow range considered in the present study. The specific fuel consumption for the star pattern is less by 40–60% as compared with the inline pattern for p/d = 1.67, Re = 50–300 and z/d = 3–7. A numerical simulation is carried out using CFD software to explain the shift in the peak heat flux away from the geometric intended location.

Microfracture for chondral defects: assessment of the variability of surgical technique in cadavers

The purpose of this study was to assess the variability of the microfracture technique when performed by experienced knee arthroscopy surgeons. Four surgeons were each asked to perform microfracture on six preformed cartilage defects in fresh human cadaveric knees. Surgeons were instructed on penetration depth, inter-hole distance, and to place the holes perpendicular to the subchondral surface. Micro-computed tomography was used to calculate depth error, inter-hole distance error, and deviation of penetration angles from the perpendicular. All surgeons misjudged depth and inter-hole distance, tending to make microfracture holes too deep (depth error 1.1mm±1.9) and too close together (inter-hole distance error: -0.8mm±0.4). Fifty-one per cent of holes were angled more than 10° from the perpendicular (range 2.6°-19.8°). Both depth and distance errors were significantly lower in the trochlear groove than on the femoral condyle (p<0.05). Surface shearing was associated with both penetration depth >4mm and angles >20°. Inter-hole infraction occurred in holes closer than 2.5mm to each other. Even experienced knee arthroscopy surgeons demonstrate inconsistency in surgical technique when performing microfracture. While further research will be required to demonstrate that these variations in surgical technique are associated with poorer clinical outcomes after microfracture, surgeons should attempt to minimizing such variations in order to prevent surface shearing and inter-hole infraction.

Growth mechanisms and process window for InAs V-shaped nanoscale membranes on Si[001

Organized growth of high aspect-ratio nanostructures such as membranes is interesting for opto-electronic and energy harvesting applications. Recently, we reported a new form of InAs nano-membranes grown on Si substrates with enhanced light scattering properties. In this paper we study how to tune the morphology of the membranes by changing the growth conditions. We examine the role of the V/III ratio, substrate temperature, mask opening size and inter-hole distances in determining the size and shape of the structures. Our results show that the nano-membranes form by a combination of the growth mechanisms of nanowires and the Stranski–Krastanov type of quantum dots: in analogy with nanowires, the length of the membranes strongly depends on the growth temperature and the V/III ratio; the inter-hole distance of the sample determines two different growth regimes: competitive growth for small distances and an independent regime for larger distances. Conversely, and similarly to quantum dots, the width of the nano-membranes increases with the growth temperature and does not exhibit dependence on the V/III ratio. These results constitute an important step towards achieving rational design of high aspect-ratio nanostructures.

Numerical and experimental investigation of a new film cooling geometry with high P/D ratio

In order to improve the coolant surface coverage, in the past years new geometries have been proposed with higher lateral fan-shaped angle and/or greater inter-hole pitch distance (P/D). Unfortunately it is not possible to increase the fan angle or the pitch distance even further without inducing a coolant separation and a drop in the overall effectiveness.This study proposes an innovative design which improves the lateral coverage and reduces the jet lift off. The results have been validated by a combination of numerical and experimental analyses: the experimental work has been assessed on a flat plate using thermo chromic liquid crystals and the results have been confirmed numerically by the CFD with the same conditions. The CFD simulations have been carried out considering a stochastic distribution for the free stream Mach number and the coolant blowing ratio.The experimental and computational results show that the inducing lateral pressure gradients there is a minimum increase in lateral averaged adiabatic effectiveness of +30% than the baseline case until a distance downstream of 20 times the coolant diameter.

Quasiperiodic plasmonic concentrators for enhanced light absorption in ultra-thin film solar cells

ABSTRACTThis report will demonstrate broadband, wide-angle, and polarization-insensitive absorption enhancement in ultra-thin films resting on metal substrates that have been etched with arrays of shallow sub-wavelength cylindrical holes. Absorption enhancement will be studied as a function of array geometry, with particular emphasis given to quasiperiodic arrays (a class of deterministic aperiodic arrays that were originally developed to tessellate 2-D planes with regular polygons). Through simulations and experimental data, it was found that absorption enhancement is heavily dependent on the rotational symmetry of the pattern of holes, as well as the inter-hole distance.

Effects of gas injection with multihole orifices in upleg snorkel on bubble behaviour and decarburisation rate during RH refining

Physical model experiments have been conducted to investigate the effects of multihole orifices in the upleg snorkel on bubble behaviour and decarburisation rate during Ruhrstahl–Heraeus refining. Bubble behaviour was recorded by a high speed video camera and a volumetric mass transfer coefficient kA/V was used to evaluate the decarburisation rate. Measurement of the volumetric mass transfer coefficient kA/V was made by means of the CO2 desorption from a NaOH solution. Pictures of bubble behaviour show that gas bubbles are generated separately from the multihole orifice in the low region of gas flowrate, but they tend to coalesce at high gas flowrate. It was demonstrated that kA/V increases with increasing gas flowrate and decreasing orifice hole diameter. In the low region of gas flowrate, kA/V for multihole orifices is larger than that for one-hole orifices. In this case, kA/V increases as the number of holes increases, and the hole distance of orifice has little effect on kA/V. However, in the high region of gas flowrate, kA/V for multihole orifices is lower than that for one-hole orifices, and kA/V decreases with the increase in orifice interhole distance. It was found that there exists a critical gas flowrate, above which kA/V for multihole orifices is lower than that for one-hole orifices. This critical value increases with increasing hole distance and hole number. Some explanations were also made in terms of bubble behaviour.

Ultrasonic transmission through multiple-sublattice subwavelength holes arrays

The ultrasonic transmission through plates perforated with 2 × 2 or 3 × 3 square array of subwavelength holes per unit cell are studied by numerical simulations. Calculations are obtained by means of a theoretical model under the rigid-solid assumption. It is demonstrated that when the inter-hole distance within the unit cell is reduced, new transmission dips appear resulting from Wood anomalies that have influence on the second and the third order Fabry–Perot peak. When the inter-hole distance within the unit cell is reduced, the transmission spectrum of the multiple-sublattice holes arrays tends to the transmission spectrum of a plate perforated with only one hole in the unit cell.

Very High Frequency Multi Hollow Cathode PECVD 장치의 수치모델링

초고주파 다중 중공 음극 방전을 이용한 플라즈마 화학 기상 증착 장치를 3차원 수치 모델링하였다. 기본적인 방전 특성을 파악하기 위하여 알곤 플라즈마를 40 MHz, 100 V, 133.3 Pa (1 Torr)의 조건에 대해서 계산하였다. 6 mm 직경의 홀을 20 mm 간격으로 배열하였고 전극 간격은 10 mm를 가정하였다. 피크 플라즈마 밀도는 홀의 하부 중앙에서 <TEX>$5{\times}10^{11}#/cm^3$</TEX> 였으며 전자 온도는 접지 상태로 가정한 기판과 챔버 벽면 주위에서 가장 높았다. 준안정 상태에 의한 2단 이온화 속도는 전자 충돌에 의한 직접 이온화보다 10배 가량 높았다. 수소에 대한 계산에서는 이온화 이외의 다양한 에너지 소모 경로가 있어서 방전의 국재화가 잘 이루어지지 않았다. 3D fluid based numerical modelling is done for a VHF multi hollow cathode array plasma enhanced chemical vapor deposition system. In order to understand the fundamental characteristics of it, Ar plasma is analyzed with a condition of 40 MHz, 100 Vrf and 1 Torr. For hole array of 6 mm diameter and 20 mm inter-hole distance, plasma is well confined within the hole at an electrode gap of 10 mm. The peak plasma density was <TEX>$5{\times}10^{11}#/cm^3$</TEX> at the center of the hole. When the substrate was assumed at ground potential, electron temperature showed a peak at the vicinity of the grounded walls including the substrate and chamber walls. The reaction rate of metastable based two step ionization was 10 times higher than the direct electron impact ionization at this condition. For <TEX>$H_2$</TEX>, the spatial localization of discharge is harder to get than Ar due to various pathways of electron impact reactions other than ionization.

Quantitative three-dimensional characterization of pearlite spheroidization

We investigated the pearlite spheroidization of a 0.8 mass% C–Fe steel under 700 °C static annealing conditions using a combination of computer-aided three-dimensional (3-D) tomography and electron back-scattered diffraction. The holes present in naturally grown cementite lamellae cause shape instability and induce shape evolution of the lamellar structure during spheroidization. 3-D visualization demonstrated that the intrinsic holes play an important role in the initiation and development of pearlite spheroidization. The hole coalescence and expansion causes the break-up up of large cementite lamellae into several long narrow ribbons. Furthermore, the growth mechanism of inter-hole coalescence is related to the ratio of half the inter-hole distance on a cementite lamella to the thickness of that lamella. The driving force for hole growth is either the difference in surface energy or the curvature between the hole edges and the adjacent flat surface of the lamella. The morphologies of cementite ribbons depend on the hole expansion position on cementite lamella, and can change their shape to cylinders or small spheres by Rayleigh’s perturbation process after prolonged spheroidization.