Search

In order to reveal the effect of channel orientations on rotational heat transfer performance, this paper presents an experimental model of AR = 4:1 smooth rectangular channel. The stationary and rotational heat transfer characteristics of the channel are studied in the range of Re = 10,000–40,000 and Ro = 0–1.23 under the channel orientation of 90° and 135°, which represent the basic one and realistic one, respectively. The experimental results indicate that for the trailing wall, the 90° channel shows a typical large range enhancement of rotational heat transfer, while the rotational effect becomes negative in most areas at 135° case. As the rotation number exceeds 0.7, the heat transfer of the trailing surface is greatly improved by rotational effect in 90° channel. When the channel was orientated at 135°, the leading surface heat transfer is more sensitive to rotation under the low rotation number (Ro

As CeO2 is a useful catalyst for soot elimination, it is important to develop CeO2 with higher contact areas, and reactivities for efficient soot oxidation and catalytic soot oxidation are basically controlled by structures and surface properties of catalysts. Herein, a Ce-Metal organic framework (MOFs) consisting of Ce and benzene-1,3,5-tricarboxylic acid (H3BTC) is employed as the precursor as CeBTC exhibits a unique bar-like high-aspect-ratio morphology, which is then transformed into CeO2 with a nanoscale bar-like configuration. More importantly, this CeO2 nanobar (CeONB) possesses porou, and even hollow structures, as well as more oxygen vacancies, enabling CeONB to become a promising catalyst for soot oxidation. Thus, CeONB shows a much higher catalytic activity than commercial CeO2 nanoparticle (comCeO) for soot oxidation with a significantly lower ignition temperature (Tig). Moreover, while soot oxidation by comCeO leads to production of CO together with CO2, CeONB can completely convert soot to CO2. The tight contact mode also enables CeONB to exhibit a very low Tig of 310 °C, whereas the existence of NO also enhances the soot oxidation by CeONB to reduce the Tig. The mechanism of NO-assisted soot oxidation is also examined, and validated by DRIFTS to identify the formation and transformation of nitrogen-containing intermediates. CeONB is also recyclable over many consecutive cycles and maintained its high catalytic activity for soot oxidation. These results demonstrate that CeONB is a promising and easily prepared high-aspect-ratio Ce-based catalyst for soot oxidation.

Graphene-Coated carbon nanofibers (G-CNFs) Foams with interconnected 3D-networks have unique physical properties that make them suitable for a wide variety of applications. However, their design and fabrication strategies entail several parameters with different strengths, anisotropy, and thermal conductivity. Tuning functional properties to meet the desired application needs a deep understanding of their microstructure. Utilizing a microstructure modeling based on a Finite Element Analysis (FEA) requires adopting an accurate yet simple approach to overcome complications associated with the unique morphological characteristics of the G-CNFs Foam, covering graphene coating thickness and high aspect ratio and tortuosity, that can be neither disregarded nor roughly approximated. Here, we introduce an innovative strategy to predict the morphological, mechanical, and thermal properties of a G-CNFs Foam with a high aspect ratio and tortuosity, as well as a significant difference in composite materials' strength to overcome modeling difficulties including meshing, coating thickness, and homogenization, to name a few. This new modeling strategy is validated with experimental data from our work and the literature and provides a reliable and straightforward approach with less computational cost.

We present a method to produce small pitch gratings for X-ray interferometric imaging applications, allowing the phase sensitivity to be increased and/or the length of the laboratory setup to be minimized. The method is based on fabrication of high aspect ratio silicon microstructures using deep reactive ion etching (Bosch technique) of dense grating arrays and followed by conformal electroplating of Au. We demonstrated that low resistivity Si substrates (, Micromachines, 12 (5), ISSN:2072-666X

Using Au chloride as precursor, Pt nanocrystals as seeds, ascorbic acid as a reducer, and CTAB as surfactant and complexing agent, extremely long Au nanorods have been grown. The influence of different parameters such as the composition of the seeds, the amount of Pt, or the type of Pt present in solution has been analyzed. These large Au NRs have been exhaustively characterized by (S)TEM, SEM and optical microscopy as well as UV-vis spectroscopy and their morphology correlated with the growth mechanism., We acknowledge financial support from Spanish MICINN MAT2006-13572-C02-02-02. M.V. thanks the Spanish MICINN for the financial support through the fellowship BES- 2007-17164, associated with the project.

With the rapid development of micro-electro-mechanical systems (MEMSs), the demand for glass microstructure is increasing. For the purpose of achieving high quality and stable machining of glass microstructures with a high aspect ratio, ultrasonic vibration is applied into the micro-wire electrochemical discharge machining (WECDM), which is proposed as ultrasonic vibration-assisted WECDM with a micro helical electrode. Firstly, the formation of a gas film on the surface of the helical electrode in WECDM machining is simulated, meaning the thickness of the gas film can be reduced by adding suitable ultrasonic amplitude, thus reducing the critical voltage, then the machining localization and stability were enhanced. Then, the micro helical electrode with a diameter of 100 &mu, m is used to carry out sets of experiments that study the influence of ultrasonic amplitude, machining voltage, duty factor, pulse frequency, and feed rate on the slit width. The experimental results show that the machining stability and quality are significantly improved by adding suitable ultrasonic amplitude. When the amplitude was 5.25 &mu, m, the average slit width was reduced to 128.63 &mu, m with a decrease of 20.78%. Finally, with the optimized machining parameters, micro planar coil structure and microcantilever structure with a high aspect ratio were fabricated successfully on the glass plate. It is proved that ultrasonic vibration-assisted WECDM with the micro helical electrode method can meet the requirements of high aspect ratio microstructure machining for hard and brittle materials.

Severe tool wear and poor surface quality are the main problems during micro machining of cemented carbide. In this work, an innovative hybrid process of laser-induced oxidation assisted micro milling (LOMM) was proposed to solve the problems. A nanosecond laser was utilized to induce oxidation of the WC-20%Co material, producing loose oxide which was easy to remove. The micro machinability of the material was improved by laser-induced oxidation. The oxidation mechanisms of cemented carbide were studied. A microgroove with a depth of 2.5 mm and aspect ratio of 5 was fabricated successfully. The milling force, surface quality and tool wear mechanisms were investigated. For comparison, a microgroove was also fabricated with conventional micro milling (COMM) using identical milling parameters. Results revealed that in LOMM the milling force and tool wear rate were extremely low during removing the oxide. The machined surface quality and dimensional accuracy achieved by LOMM were superior to those obtained by COMM. The surface roughness Sa of the microgroove bottom reached 88 nm in LOMM, while the cross-sectional geometry of the microgroove was a trapezoid. Perpendicularity of the microgroove sidewall machined by LOMM was better than that by COMM. The tool wear forms in LOMM were coating spalling and slight tool nose breakage. Compared with COMM, the tool life in LOMM was prolonged significantly. It indicates that the proposed hybrid process is an effective and efficient way to fabricate high aspect ratio micro-features with high dimensional accuracy.

The vapor-liquid-solid (VLS) process was applied to fabricate zinc oxide nanowires (ZnO NWs) with a different aspect ratio (AR), morphological, and optical properties. The ZnO NWs were grown on a system that contains a quartz substrate with transparent conductive oxide (TCO) thin film followed by an Al-doped ZnO (AZO) seed layer; both films were grown by magnetron sputtering at room temperature. It was found that the ZnO NWs presented high crystalline quality and vertical orientation from different structural and morphological characterizations. Also, NWs showed a good density distribution of 69 NWs/μm2 with a different AR that offers their capability to be used as possible photoelectrode (anode) in potential future device applications. The samples optical properties were studied using various techniques such as photoluminescence (PL), absorption, and transmittance before and after sensitization with N719 dye. The results demonstrated that NW with 30 nm diameter had the best characteristics as feasible photoelectrode (anode) (high absorption, minimum recombination, high crystallinity). Also, the present samples optical properties were found to be improved due to the existence of N719 dye and Au nanoparticles on the tip of NWs. NWs grown in this work can be used in different photonic and optoelectronic applications.

The movable super-diffraction optical needle (MSON) is a tightly focused beam like a &ldquo, needle&rdquo, which can realize vector scanning on the focusing plane. Not only does it have a long focal depth, but its resolution also exceeds the diffraction limit. The modulation and control technology required for generating MSON by oblique incidence is explored in this manuscript for the purpose of processing high-aspect-ratio, sub-wavelength structures. As the optical needle generated by traditional methods is static and sensitive to variation of the angle information of the incident beam, here we introduce a confocal scanning system by using a two-dimensional galvanometer system, a scan lens, and a tube lens to control the oblique incidence angle. The effects of the oblique incidence angle on the resolution, depth of focus, uniformity, and side lobes of the MSON were analyzed. Further, the voltage-controlled liquid crystal located between the scan lens and the 2D galvanometer system can be used to compensate for the additional phase difference caused by oblique incidence. The aspect ratio is defined as the ratio of depth of focus to resolution. By modulating and controlling the light field, the MSON with high aspect ratio (7.36), sub-diffractive beam size (0.42&lambda, ), and long depth of focus (3.09&lambda, ) has been obtained with homogeneous intensity, and suppressed side lobes. High speed, high axial positioning tolerance, and high-resolution laser processing can also be achieved, which removes the restrictions presented by traditional laser processing technology, for which high resolution and long depth of focus cannot be achieved simultaneously.

This work reports a batch fabrication process for silicon nanometer tip based on isotropic inductively coupled plasma (ICP) etching technology. The silicon tips with nanometer apex and small surface roughness are produced at wafer-level with good etching homogeneity and repeatability. An ICP etching routine is developed to make silicon tips with apex radius less than 5 nm, aspect ratio greater than 5 at a tip height of 200 nm, and tip height more than 10 &mu, m, and high fabrication yield is achieved by mask compensation and precisely controlling lateral etch depth, which is significant for large-scale manufacturing.

High-aspect-ratio nanostructures have emerged as versatile platforms for intracellular sensing and biomolecule delivery. Here, we present a microfabrication approach in which a combination of reactive ion etching protocols were used to produce high-aspect-ratio, nondegradable silicon nanoneedle arrays with tip diameters that could be finely tuned between 20 and 700 nm. We used these arrays to guide the long-term culture of human mesenchymal stem cells (hMSCs). Notably, we used changes in the nanoneedle tip diameter to control the morphology, nuclear size, and F-actin alignment of interfaced hMSCs and to regulate the expression of nuclear lamina genes, Yes-associated protein (YAP) target genes, and focal adhesion genes. These topography-driven changes were attributed to signaling by Rho-family GTPase pathways, differences in the effective stiffness of the nanoneedle arrays, and the degree of nuclear membrane impingement, with the latter clearly visualized using focused ion beam scanning electron microscopy (FIB-SEM). Our approach to design high-aspect-ratio nanostructures will be broadly applicable to design biomaterials and biomedical devices used for long-term cell stimulation and monitoring.

Etching rate is a major concern for the effective mass production of high-aspect-ratio microstructures, especially in p-type silicon. In this work, controlled electrochemical growth of high-aspect-ratio (from 15 to 110) macropores in p-type silicon at ultrafast etching rate (from 16 to 30 µm min−1) has been studied. Based on current-burst-model, pore formation was systematically investigated from the nucleation phase to stable pore growth. Good macropores with depth up to 180 µm and aspect ratio beyond 110 was achieved in just 11 min. This sets a new record on state-of-the-art p-type silicon microfabrication and can promote the development of microdevices.

The quest to sculpture materials as small and deep as possible is an ongoing topic in micro- and nanofabrication. For this, the Bosch process has been widely used to achieve anisotropic silicon microstructures with high aspect ratio. Reactive ion etching (RIE) lag is a phenomenon in which etch rate depends on the opening areas of patterns, aspect ratio of the trenches and other geometrical factors. The lag not only gives a non-uniform distribution of scallop size, but it also sets a limit for the maximum achievable aspect ratio. The latter since the mask suffers from persistent erosion. While different kinds of hard masks have been suggested to ensure a longer total etch time, here we report a correctly tuned 3-steps Bosch process - called DREM (Deposit, Remove, Etch, Multistep) – without mask erosion. The erosion-free feature is independent of the type of mask. For example, an aspect ratio of more than 50 is achieved for trenches with 1 μm linewidths, while no erosion is observed for 360 nm thin standard photoresists. The mechanism behind this extraordinary infinite selectivity is mainly due to the depletion of C4F8 deposition species. Furthermore, a linear ramping of the etch step duration is performed to achieve a uniform distribution of scallop sizes along the etch profile. This outperforms the usual broad scallop size distribution when no parameter ramping is performed and improves the straightness of the etch profile considerably, in addition, it allows an easier way to control periodic sidewall shaping. e.g., a sausage-chain-like feature is demonstrated with an almost perfect periodicity.

Laser beam machining (LBM) is capable of almost force-free 2D and 3D machining of any kind of material without tool wear. This process is defined by many parameters, such as pulse energy, frequency, scanning velocity and number of scanning repetitions. Modern laser machines provide high energy at shorter pulse durations and have more precise positioning systems than machines of the past. These can easily fulfil today's continuous changing product requirements. For an overall understanding, an extensive amount of experimentation is required to display the interaction laws and dependencies between process parameters, as well as the resulting shapes and quality of the machined surface. By using an ultrashort pulse (USP) laser, a wide range of customer oriented applications in micrometer scale can be addressed, which leads to precise ablation with minimal thermal damage. This paper provides knowledge on the machining of copper micro features with high aspect ratio and a 532 nm wavelength laser beam. Aspect ratios up to 17 and slot widths smaller than 20 μm were performed with a beam radius ω0 smaller than 5 μm and pulse duration smaller than 12 ps. For desired slot geometries, necessary process parameters were developed and their physical limits are shown and discussed. The limits of minimum structure size have been analysed by observing the remaining material between slots at decreasing distances. Material debris deposits on the non-machined surface, as well as chemical changes of copper, were analysed using scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDX). Special attention was given to the taper angle, which arises due to the Gaussian distribution of energy in the laser beam., Procedia CIRP, 68, ISSN:2212-8271, 19th CIRP Conference on Electro Physical and Chemical Machining

High aspect ratio microstructures (HARMS) are of great importance for many application fields. Many defects are generated during the fabrication processes, especially in line microstructures, and it is necessary to examine the quality of the structures after each process. However, there is no suitable efficient nondestructive detection method to monitor microstructures during the fabrication processes. In this paper, an optical detection method capable of detecting the structures by analyzing the reflection of light on the line HARMS is proposed. According to the image of reflected visible light, this method can determine whether there are defects in structures, so as to realize efficient detection. Preliminary simulations and experiments have been performed to confirm the feasibility and validity of the proposed method for detecting line microstructures. This method is expected to obtain more information about microstructures by further optimizing system parameters.

This paper demonstrates a 3D microlithography system where an array of 5 mm Ultra Violet-Light Emitting Diode (UV-LED) acts as a light source. The unit of the light source is a UV-LED, which comes with a length of about 8.9 mm and a diameter of 5 mm. The whole light source comprises 20 &times, 20 matrix of such 5 mm UV-LEDs giving a total number of 400 LEDs which makes it a very favorable source with a large area for having a batch production of the desired microstructures. This light source is able to give a level of precision in microfabrication which cannot be obtained using commercial 3D printers. The whole light source performs continuous rotational movement once it is turned on. This can also move up and down in a vertical direction. This multidirectional light source also comprises a multidirectional sample holder. The light source teaming up with the multidirectional sample holder highly facilitates the process of fabrication of a huge range of 3D structures. This article also describes the different levels of characterization of the system and demonstrates several fabricated 3D microstructures including high aspect ratio vertical micro towers, twisted turbine structures, triangles, inclined pillar &lsquo, V&rsquo, structures, and hollow horn structures as well.

We fabricated two-dimensional arrays of periodic, widely-spaced pillars using deep reactive ion etching of silicon. To avoid the formation of micro-grass in the large open areas we used sacrificial structures surrounding the widely-spaced pillars. The use of sacrificial structures results in a denser pattern where the formation of grass is less likely to happen. We were able to remove the sacrificial structures without damaging the main array of pillars by using a modified Bosch process. The roughness remaining after removal of the sacrificial structures was evaluated using optical profilometry. Using this method, we were able to pattern grass-free arrays of widely-spaced 12 μm diameter pillars of 9:1 aspect ratio, with hexagonal and square distributions.

This work was supported by the Portuguese Foundation for Science and Technology (FCT) through the following project: UID/Multi/04044/2013 and PAMI ROTEIRO/0328/2013 (Nº 022158). In addition, the authors acknowledge the funding from the project Coolgrafeno, copromoção n. 17883 from the Portuguese National Innovation Agency. For many years traditional injection moulding has been the norm for obtaining polymer based products, and yet this cycle still shows potential for improvement. This paper will encompass the potential in the thermal part of the cycle, by introducing a novel approach to conventional tubular cooling designs, empowered by additive technologies this reiterates what’s being known as conformal cooling. Different geometries and techniques are compared to determine the optimal cross section layout of the fluid channels and inner surface of the moulding parts. If the cooling achieved is sufficiently fast the crystallographic growth of the material can be manipulated to obtain specific properties observable in the mesoscale. This however can be transversely applied in other heat exchanging structures in future studies. info:eu-repo/semantics/publishedVersion

Metal-assisted chemical etching (MACE) is a site-selective etching process produced by a catalyst reaction at the interface between noble metal and silicon. This paper aims to make clear the applicability of sphere lithography and MACE to the fabrication of high aspect ratio Si nanostructures. The capacity to control the etched profiles and the scale extension are investigated. First, silica particles (e.g. φ1 μm) were self-assembled on a Si substrate. After the reduction of particle size via argon ion bombardment, a gold layer was deposited using the particles as a mask. The substrate was then etched with a mixture of hydrofluoric acid and hydrogen peroxide. It was found that an array of nanopillars with a regular pitch, good separation, and an aspect ratio of about 52 was produced. The effects of MACE conditions on final profiles were clarified. A limitation of this approach is the small (several millimeters) area fabricated due to the dependence on the vacuum technique (ion bombardment, Au deposition), and the size of the area limits its practical applications. Thus, Ag nanoparticles (e.g. φ150 nm) were applied. The relationship between the concentration of the Ag suspension, the Ag assembled layer, and the morphology of MACE structures was made clear. A spray method was applied to extend the deposited area of Ag particles up to φ100 mm. Finally, the effects of the cross-sectional profile on the contact angle of a water droplet were examined. By applying a high aspect ratio nanostructure on the substrate, the water contact angle increased up to 153 degrees while that without the structure is 58 degrees.

Despite the fact that the resolution of conventional contact/proximity lithography can reach feature sizes down to ~0.5-0.6 micrometers, the accurate control of the linewidth and uniformity becomes already very challenging for gratings with periods in the range of 1-2 {\mu}m. This is particularly relevant for the exposure of large areas and wafers thinner than 300{\mu}m. If the wafer or mask surface is not fully flat due to any kind of defects, such as bowing/warpage or remaining topography of the surface in case of overlay exposures, noticeable linewidth variations or complete failure of lithography step will occur. We utilized the newly developed Displacement Talbot lithography to pattern gratings with equal lines and spaces and periods in the range of 1.0 to 2.4 {\mu}m. The exposures in this lithography process do not require contact between the mask and the wafer, which makes it essentially insensitive to surface planarity and enables exposures with very high linewidth uniformity on thin and even slightly deformed wafers. We demonstrated pattern transfer of such exposures into Si substrates by reactive ion etching using the Bosch process. An etching depth of 30 {\mu}m or more for the whole range of periods was achieved, which corresponds to very high aspect ratios up to 60:1. The application of the fabricated gratings in phase contrast x-ray imaging is presented.

The file attached to this record is the author's final peer reviewed version. The Publisher's final version can be found by following the DOI link. A neural electrode interface material is a key component for effective stimulation and recording of neuralactivity. The fundamental requirement of a neural electrode is for it to be able to deliver adequate charge to targeted neuronal population. Coating electrode surfaces with nanostructured material not only provides an increase in surface area, providing relatively more active sites for charge delivery than planar systems, but also allows for the reduction of electrode dimension to reduce invasiveness and increase selectivity. In this work, titanium nitride nanowires (TiN-NWs) synthesised by novel nitridation process in Plasma Enhanced Chemical Vapour Deposition (PECVD) is suggested as an enhanced coating material for neural electrodes. The synthesis involved the solution growth of crystalline titanium oxide nanorods (TiO⁠2-NRs) from a sputtered TiN nucleation layer followed by nitridation. TiO⁠2-NRs exhibited high aspect ratio of 23.1 and were converted into TiN after one hour of nitridation at 600°C. Evidence of conversion was studied by Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and Transmission electron microscopy (TEM). The nitridation temperature and time reported here are the lowest and shortest as compared to the literature. The near-stoichiometric TiN-NWs (x=0.49) achieved in this work were used subsequently for electrochemical characterisation through Cyclic Voltammetry (CV). The capacitance of relatively high aspect TiN-NWs was 3.78mF/cm⁠2⁠, which was a 5-fold enhancement compared to thin film of TiN layer (0.7 mF/cm⁠2). A stability test of the nanowires were performed in which the capacitance remained relatively unchanged.

The application of luminescent materials in display screens and devices requires micropatterned structures. In this work, we have successfully printed microstructures of a two-dimensional (2D), orange-colored organic/inorganic hybrid perovskite ((C6H5CH2NH3)2PbI4) using two different soft lithography techniques. Notably, both techniques yield microstructures with very high aspect ratios in the range of 1.5–1.8. X-ray diffraction reveals a strong preferential orientation of the crystallites along the c-axis in both patterned structures, when compared to nonpatterned, drop-casted thin films. Furthermore, (time-resolved) photoluminescence (PL) measurements reveal that the optical properties of (C6H5CH2NH3)2PbI4 are conserved upon patterning. We find that the larger grain sizes of the patterned films with respect to the nonpatterned film give rise to an enhanced PL lifetime. Thus, our results demonstrate easy and cost-effective ways to manufacture patterns of 2D organic/inorganic hybrid perovskites, while even improving their optical properties. This demonstrates the potential use of color-tunable 2D hybrids in optoelectronic devices.

We have studied the fabrication of line-like and pillar-like periodic microstructures on stainless steel by means of direct laser interference patterning. A picosecond (10 ps) pulsed Nd:YAG laser operating at 1064 nm wavelength was used to produce the microstructures with spatial periods ranging from 2.6 μm to 5.2 μm. By varying the laser parameters (laser fluence, pulse-to-pulse overlap) structure depths ranging from 500 nm to nearly 11.5 μm could be obtained. Furthermore, low and high frequency laser induced periodic surface structures (LIPSS) have been generated, resulting in three-level multi-scaled patterns. The orientation of the laser induced periodic structures with respect to the interference patterns could be adjusted by controlling the laser beam polarization. Finally, static water contact angle measurements are performed to investigate its correlation with the surface morphology. The treated surfaces are characterized using confocal and scanning electron microscopy.

The use of SU-8 as precursor for glass-like carbon, or glassy carbon, is presented here. SU-8 carbonizes when subject to high temperature under inert atmosphere. Although epoxy-based precursors can be patterned in a variety of ways, photolithography is chosen due to its resolution and reproducibility. Here, a number of improvements to traditional photolithography are introduced to increase the versatility of the process. The shrinkage of SU-8 during carbonization is then detailed as one of the guidelines necessary to design carbon patterns. A couple of applications—(1) carbon-electrode dielectrophoresis for bioparticle manipulation; and (2) the use of carbon structures as micro-molds are also presented.

A major breakthrough in UV-LIGA (Lithographie, Galvanoformung and Abformung) started with the use of epoxy-based EPON® SU-8 photoresist in the mid-1990s. Using this photoresist has enabled the fabrication of tall and high aspect ratio structures without the use of a very expensive synchrotron source needed to expose the photoresist layer in X-ray LIGA. SU-8 photoresist appeared to be well-suited for LIGA templates, but also as a permanent material. Based on UV-LIGA and SU-8, Mimotec SA has developed processes to manufacture mold inserts and metallic components for various market fields. From one to three-level parts, from Ni to other materials, from simple to complicated parts with integrated functionalities, UV-LIGA has established itself as a manufacturing technology of importance for prototyping, as well as for mass-fabrication. This paper reviews some of the developments that led to commercial success in this field.

High aspect ratio (HAR) ultrafine tapered holes (diameter &le, 5 &mu, m, AR &ge, 5) are the most important elements for some high-tech perforated metallic products, but they are very difficult to manufacture. Therefore, this paper proposes a nontraditional over-growth electroforming process. The formation mechanism of the HAR ultrafine tapered holes is investigated, and the factors controlling the geometric shape evolution are analyzed numerically. It was found that the geometric shape and dimensions of the holes are highly dependent on the diameter and thickness of the photoresist film patterns, but are hardly affected by the spacing between two neighboring patterns, the achievable diameter for a given hole depth becomes small with the increasing pattern diameter, but it becomes big with the increasing pattern thickness. These correlations can be well interpreted by the established two empirical equations that characterize the relationship between the minimum orifice of the tapered hole and the structural parameters of the photoresist film patterns previously formed on the substrate. Application of the fabricated 1500 tapered holes with 3-&mu, m diameter and 17-AR as the nozzles of the medical precision nebulizer is also examined. The studies show that the over-growth electroforming process is highly applicable in fabricating the perforated metallic plate with HAR ultrafine tapered holes.

Yamani, Zain/0000-0002-6031-9385; Enders, Brian/0000-0002-5284-4040; Tokmoldin, Serekbol/0000-0003-0633-4733; BAHCECI, ersin/0000-0002-7719-6051, WOS: 000477701000088, We use silicon having multiple crystalline orientation domains and high metal doping in metal assisted chemical etching (MACEtch) in HF/H2O2. In device-quality silicon, MACEtch produces high-aspect ratio anisotropic (I-D) structures (wires, columns, pores or holes) and to a lesser degree non-high-aspect ratio luminescent (0-D) nano structures. While the 1-D structure symmetry is understood in terms of crystallography axis-dependent etching, predominantly along the < 100 > direction, the isotropic 0-D spherical symmetry etching is not understood. We observe in silicon having multiple crystalline orientation domains formation of metal tips (needles or whiskers) of diameters as small as 2-3 nm that bridge the metal to silicon and cause AFM/STM-like nanofabrication, producing 0-D mounds, indentations, or clusters. The formation of sharp needles can be understood in terms of charge injection/electric breakdown between metal clusters and silicon due to charge build-up. Silicon with high degree of impurities as well as with multiple crystalline orientation domains allow imaging these effects using electron spectroscopy without cross sectional cuts. (C) 2019 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

Deep proton writing ( DPW) is a fabrication technology developed for the rapid prototyping of polymer microstructures. We use polymethylmethacrylate (PMMA) substrates, which act as a positive resist, for irradiation with a collimated 12-MeV energy proton beam. Using 12 MeV enables the irradiation of increasingly thick PMMA substrates with less conicity of the sidewalls compared to the lower energies used in previous work. A microhole of 47.7 mu m diameter over a depth of 1 mm is achieved, leading to a maximum aspect ratio of 21:1. The sidewalls of the irradiated structures show a slightly conical shape and their root-mean-square surface roughness is lower than 50 nm averaged over 72 measured areas of 56 mu m x 44 mu m. This means that DPW components have optical surface quality sidewalls for wavelengths larger than 400 nm. Based on the trade-off among the sidewall roughness, conicity, and the development time, we determine that the optimal proton fluence for 12-MeV DPW in PMMA is 7.75 x 10(6) mu m(- 2.) Finally, we discuss some high aspect ratio microstructures with optical surface quality that were created with DPW to be used for a myriad of applications, such as micromirrors, microlenses, optofluidic devices, and high-precision alignment structures for single-mode optical fiber connectors. (C) 2016 Society of Photo-Optical Instrumentation Engineers (SPIE)

International audience; Wetting efficiency of microstructures or nanostructures patterned on Si wafers is a real concern in integrated circuits manufacturing. We present here a high-frequency acoustic method which enables the local determination of the wetting state of a liquid on real DTI and TSV structures. Partial wetting states for non-hydrophobic surfaces or low surface tension liquids are detectable with this method. Filling time of TSV structures has also been measured.

A new and versatile technique for the wafer scale nanofabrication of silicon nanowire (SiNW) and multiwalled carbon nanotube (MWNT) tips on atomic force microscope (AFM) probes is presented. Catalyst material for the SiNW and MWNT growth was deposited on prefabricated AFM probes using aligned wafer scale nanostencil lithography. Individual vertical SiNWs were grown epitaxially by a catalytic vapor-liquid-solid (VLS) process and MWNTs were grown by a plasma-enhanced chemical vapor (PECVD) process on the AFM probes. The AFM probes were tested for imaging micrometers-deep trenches, where they demonstrated a significantly better performance than commercial high aspect ratio tips. Our method demonstrates a reliable and cost-efficient route toward wafer scale manufacturing of SiNW and MWNT AFM probes.

Instability of a thin film attached to a compliant substrate often leads to emergence of exquisite wrinkle patterns with length scales that depend on the system geometry and applied stresses. These patterns have potential applications in many areas including tissue engineering, flexible electronics and semiconductor industry. In this talk, we will present several novel techniques for polymer surface engineering, including creation of controlled hierarchical patterns and wrinkles with high amplitude/wavelength aspect ratio. The applications of these techniques in microfluidics, optics, and also in development of biomimetic surfaces will be discussed.

In this study, the filling process of high aspect ratio through-silicon-vias (TSVs) under dense conditions using the electroplating method was efficiently achieved and optimized. Pulsed power was used as the experimental power source and the electroplating solution was prepared with various additive concentrations. Designed control variable experiments were conducted to determine the optimized method. In the control variable experiments, the relationship of multiple experimental variables, including current density (0.25&ndash, 2 A/dm2), additive concentration (0.5&ndash, 2 mL/L), and different shapes of TSVs (circle, oral, and square), were systematically analyzed. Considering the electroplating speed and quality, the influence of different factors on experimental results and the optimized parameters were determined. The results showed that increasing current density improved the electroplating speed but decreased the quality. Additives worked well, whereas their concentrations were controlled within a suitable range. The TSV shape also influenced the electroplating result. When the current density was 1.5 A/dm2 and the additive concentration was 1 mL/L, the TSV filling was relatively better. With the optimized parameters, 500-&mu, m-deep TSVs with a high aspect ratio of 10:1 were fully filled in 20 h, and the via density reached 70/mm2. Finally, optimized parameters were adopted, and the electroplating of 1000-&mu, m-deep TSVs with a diameter of 100 &mu, m was completed in 45 h, which is the deepest and smallest through which a three-dimensional inductor has ever been successfully fabricated.

We report morphological and ferromagnetic property control in ZnO nanorod structures by an optimum doping of Ni and Li. Nanostructures of Zn 0.97-xNi0.03LixO (x = 0, 0.03, 0.05, 0.08, and 0.10) are prepared by a solvothermal method. High aspect ratio (5-15) ZnO nanorods transform to particles (with 1-3 aspect ratio) influenced by 3 at. % Ni substitution in ZnO (Zn0.97Ni0.03O). It is remarkable to note that the Zn0.97Ni0.03O particles completely retain the nanorod shape with significantly increased aspect ratio (15-30) when 3 at.% Li ions are codoped in Zn0.97Ni0.03O (Zn 0.94Li0.03Ni0.03O). Li substitution also enhances ferromagnetism with largest magnetization (0.8 emu�g-1) observed for Zn0.94Li0.03Ni0.03O. For Li concentration >3 at.%, the aspect ratio as well as the magnetization decreased considerably. These experimental observations are explained by first-principles modeling. At low Li-on-Zn acceptor concentrations, the total magnetization is increased by lower Ni d-state populations, whereas at higher Li concentrations the population of ZnO host states decreases the ferromagnetism by induced magnetic moments on the oxygens. We discuss the significant implications of these results on the nanorods structures of room temperature ferromagnetic materials, which are expected to play pivotal role in developing spintronic devices. � 2010 American Chemical Society.

A gap with variable geometry is presented for both cantilever beam and fixed-fixed beam actuators as a method to reduce the pull-in voltage while maintaining a required displacement. The method is applicable to beams oriented either in a plane parallel to or perpendicular to a substrate, but is most suitable for vertically oriented (lateral) beams fabricated with a high aspect ratio process where variable gap geometry can be implemented directly in the layout. Finite element simulations are used to determine the pull-in voltages of these modified structures. The simulator is verified against theoretical pull-in voltage equations as well as previously published finite element simulations. By simply varying the gap in a linear fashion the pull-in voltage can be reduced by 37.2% in the cantilever beam case and 29.6% in the fixed-fixed beam case over a structure with a constant gap. This can be reduced a further 4.8% by using a polynomial gap shape (n = 4/3) for the cantilever beam and 1.2% for the fixed-fixed beam by flattening the bottom of the linearly varying gap.

An IC-compatible technique for photonic crystal sensors is presented here to fabricate dense arrays of high aspect ratios nanopillars, which are made of extremely hard materials that are difficult to shape, such as TiO 2 . This technique, called Atomic layer deposition ARrays Defined by Etch-back technique (AARDE), can significantly reduce direct bombardment on the functional surfaces and allows the precise control of the size of the densely spaced high pillars. A case study of an array of 1 μm pitch and 1.7 μm high TiO 2 pillars is investigated. Starting from 145 nm radius Si rods, the pillars are coated with a 78 nm thick ALD TiO 2 layer and subsequently uncapped by a short time plasma etching. The exposed Si cores are then removed and a second ALD deposition is used to refill the opened holes and extend the pillar radius to the desired value.

Three consecutive etching steps resulting in multi-height structures from overlapping etches.Display Omitted We present the fabrication of injection molded multi-height surface structures.We use a random mask, diffusion limited growth and electroforming a polymer foil.We find that the receding contact angle governing contact angle hysteresis.We find that introduction of pinning sites dominates the wetting behavior. We present the fabrication process for injection molded multi-height surface structures for studies of wetting behavior. We adapt the design of super hydrophobic structures to the fabrication constrictions imposed by industrial injection molding. This is important since many super hydrophobic surfaces are challenging to realize by injection molding due to overhanging structures and very high aspect ratios. In the fabrication process, we introduce several unconventional steps for producing the desired shapes, using a completely random mask pattern, exploiting the diffusion limited growth rates of different geometries, and electroforming a nickel mold from a polymer foil. The injection-molded samples are characterized by contact angle hysteresis obtained by the tilting method. We find that the receding contact angle depends on the surface coverage of the random surface structure, while the advancing contact angle is practically independent of the structure. Moreover, we argue that the increase in contact angle hysteresis correlates with the concentration of pinning sites among the random surface structures.

High aspect ratio TiO2 nanoflakes are synthesized by a one‐step modified surface hydrolysis method. Surface morphology and physical dimensions are characterized using scanning electron microscopy, laser diffraction analysis, and transmission electron microscopy. Microsized flakes having a thickness ≈40 nm are successfully synthesized by spreading an oil phase consisting of titanium tetraisopropoxide and a low surface tension hydrocarbon on the surface of water. Pure anatase phase crystalline titania nanoflakes are obtained by calcining at 400 °C without changing the shape and thickness of flakes. Relatively higher specific surface area (2–6 times) and less crystal defects enhance photocatalytic activities of nanoflakes due to more surface reaction sites and the suppression of fast recombination. By performing dye degradation under ultraviolet illumination, titania nanoflakes exhibit the higher photocatalytic efficiency over the commercial photocatalyst, Degussa P25. As far as it is known, this method is the most efficient and cost effective process for making low‐dimensional nanomaterials in a continuous manner. These titania flakes can be easily separated from the treated water by simply sedimentation or filtration and therefore is very suitable for water purification application.

High aspect ratio three-dimensional micro- and nanopatterns have important applications in diverse fields. However, fabricating these structures by a nanoimprinting method invites problems like collapse, dislocation, and defects. Finite-element analysis (FEA) is a good approach to help understand the filling process and stress distribution. The FEA method was employed to simulate the nanoimprinting process using positive and negative molds with aspect ratios of 1:1, 3:1, 5:1, and 7:1. During the filling process, the resist adjacent to boundaries has the maximum displacement. The corners of contact areas between the protruding part of the mold and the resist has the maximum Von Mises stress. For both positive and negative molds, the maximum stress in the mold increases with aspect ratio. However, filling up negative molds is more difficult than positive ones. With the same aspect ratio, the maximum stress in a negative mold is approximately twice as large as that in a positive one.

Microchannel plate (MCP) as a key part is a kind of electron multiplied device applied in many scientific fields. Oxide thin films such as zinc oxide doped with aluminum oxide (ZnO:Al2O3) as conductive layer and pure aluminum oxide (Al2O3) as secondary electron emission (SEE) layer were prepared in the pores of MCP via atomic layer deposition (ALD) which is a method that can precisely control thin film thickness on a substrate with a high aspect ratio structure. In this paper, nano-oxide thin films ZnO:Al2O3 and Al2O3 were prepared onto varied kinds of substrates by ALD technique, and the morphology, element distribution, structure, and surface chemical states of samples were systematically investigated by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and X-ray photoemission spectroscopy (XPS), respectively. Finally, electrical properties of an MCP device as a function of nano-oxide thin film thickness were firstly studied, and the electrical measurement results showed that the average gain of MCP was greater than 2,000 at DC 800 V with nano-oxide thin film thickness approximately 122 nm. During electrical measurement, current jitter was observed, and possible reasons were preliminarily proposed to explain the observed experimental phenomenon.

International audience; The BPN is a negative photoresist, sensitive in the UV at 365 nm and was previously dedicated for Wafer Level Packaging applications. This photoresist offers the advantage of forming thick layers; however, it suffers from low aspect ratio (2:1 declared by the supplier). This work reports the BPN’s technological process that allows forming 200–800 μm thick molds for electroplating purposes. Our results revealed an aspect ratio as high as 17:1 while having vertical sidewalls using conventional photolithography.

Pinning and wicking of a liquid meniscus in a square array of pillars is investigated in numerical energy minimizations and compared to wetting experiments. Our combined study shows that criteria for spontaneous film formation, based on thermodynamic considerations as well as on simple geometric modelling of the meniscus shape, are insufficient to predict the onset of wicking. High aspect ratio pillars with a square cross-section may display a re-entrant pinning regime as the density of the pillars is increased, a behaviour that is captured by neither of the aforementioned models. Numerically computed energy landscapes for the advancing meniscus allow us to explain the re-entrant behaviour in terms of energy barriers between topologically different meniscus shapes. Our numerical results are validated by wicking experiments where for the material contact angle θ₀ = 47° the re-entrant behaviour is present for square pillars and absent for pillars with circular cross section. Refereed/Peer-reviewed

The present work considers the aero-thermal characterization of a rib-roughened cooling channel for the trailing edge of gas turbine blades, and is based on previous findings from a smooth channel configuration. The passage is characterized by a trapezoidal cross section with high aspect-ratio, radial inlet flow, and coolant discharge at both model tip and trailing side, where seven elongated pedestals are installed. In this study, heat transfer augmentation is achieved by placing inclined squared ribs on the channel central portion. RANS simulations with a SST turbulence model were performed using the commercial solver ANSYS CFX®v14. The numerical tool was first validated on the available experimental data and, subsequently, its capabilities were exploited in a wider range of working conditions, namely at higher rotation speed and different channel orientation. In this way it was possible to highlight the effects that ribs and working conditions have on the development of both flow and thermal fields. The results show that rotation and channel orientation produce contrasting effects. On the rib-roughened wall, rotation/orientation generates an increase/decrease of the heat transfer; conversely, on the trailing side region rotation/orientation has a negative/positive effect on the thermal field.

Sub-100-nm silicon nanohole arrays were fabricated by a combination of the site-selective electroless deposition of noble metals through anodic porous alumina and the subsequent metal-assisted chemical etching. Under optimum conditions, the formation of deep straight holes with an ordered periodicity (e.g., 100 nm interval, 40 nm diameter, and high aspect ratio of 50) was successfully achieved. By using the present method, the fabrication of silicon nanohole arrays with 60-nm periodicity was also achieved.

This paper reports a fabrication approach for very high aspect ratio through silicon vias (TSVs). The metal filling of the through via holes is implemented by adapting standard wire bonding technology. TSVs with a diameter of 30 μm and aspect ratios between 10:1 and 20:1 have been fabricated. Basic electrical characterization and optical inspection have been conducted to verify the resistance and integrity of the metal and insulator filling of the TSV. QC 20131007

DC winding losses remain a major roadblock in realizing high efficiency micro-magnetic components (inductors/transformers). This paper reports an optimized photoresist process using negative tone and acrylic based THB-151N (from JSR Micro), to achieve one of the highest aspect ratio (17:1) and resolution (~5 µm) resist patterns for fabrication of thick (~80 µm) micro-winding using UV lithography. The process was optimized to achieve photoresist widths from 5 µm to 20 µm with resist thickness of ~85 µm in a single spin step. Unlike SU-8, this resist can be readily removed and shows a near-vertical (~91°) electroplated Cu side-wall profile. Moreover, the high resolution compared to available resist processes enables a further reduction in the footprint area and can potentially increase the number of winding thereby increasing the inductance density for micro-magnetic components. Resistance measurements of electroplated copper winding of air-core micro-inductors within the standard 0402 size (0.45 mm2 footprint area) suggested a 42% decrease in resistance (273 mΩ–159 mΩ) with the increase in electroplated Cu thickness (from 50 µm to 80 µm). Reduction of the spacings (from 10 µm to 5 µm) enabled further miniaturisation of the device footprint area (from 0.60 mm2 to 0.45 mm2) without significant increase in resistance.

We have fabricated very-high-aspect-ratio (VHAR) silicon and metal microstructures in complex geometric patterns. The recently developed surfactant-added tetramethylammonium hydroxide etching allows the formation of V-grooves in any pattern, i.e., not limited by the crystal direction, on a silicon surface. As the resulting sharp pits allow very deep photoelectrochemical etching, VHAR silicon microstructures (4-μm-wide and over-300-μm-deep trenches) are successfully fabricated in complex patterns (spiral and zigzag demonstrated), overcoming the prevailing limitations of simple pores and straight trenches. Furthermore, by filling the VHAR silicon mold with nickel and removing the silicon, high-aspect-ratio metal microstructures of complex patterns are also obtained. These VHAR microstructures in complex patterns, which are structurally much stronger than the simple posts and straight plates, overcome the stiction problem even when densely populated. © 2012 IEEE.

The recent development of ultrafast laser ablation technology in precision micromachining has dramatically increased the demand for reliable and real-time detection systems to characterize the material removal process. In particular, the laser percussion drilling of metals is lacking of non-invasive techniques able to monitor into the depth the spatial- and time-dependent evolution all through the ablation process. To understand the physical interaction between bulk material and high-energy light beam, accurate in-situ measurements of process parameters such as the penetration depth and the removal rate are crucial. We report on direct real time measurements of the ablation front displacement and the removal rate during ultrafast laser percussion drilling of metals by implementing a contactless sensing technique based on optical feedback interferometry. High aspect ratio micro-holes were drilled onto steel plates with different thermal properties (AISI 1095 and AISI 301) and Aluminum samples using 120-ps/110-kHz pulses delivered by a microchip laser fiber amplifier. Percussion drilling experiments have been performed by coaxially aligning the diode laser probe beam with the ablating laser. The displacement of the penetration front was instantaneously measured during the process with a resolution of 0.41 μm by analyzing the sawtooth-like induced modulation of the interferometric signal out of the detector system.

International audience; This work deals with recent advances in the microfabrication process technology for medium to high-aspect ratiostructures fabricated by UV photolithography using different kinds of photoresists. The resulting structures were used asmolds and will be transformed into metal structures by electroplating. Two types of photoresists are compared: epoxybased(negative) SU-8 and acrylate-based (negative) Intervia BPN. This work was prompted by the need to find analternative to SU-8 photoresist which is difficult to process and remove after electroplating. The results presented in thispaper open up new possibilities for low-cost processes using electroplating in MEMS applications.

International audience; Ultrafast laser pulses are a powerful tool to process dielectrics. Here, we review our recent work concerning high aspect ratio micro and nanochannel processing in glass. We show how femtosecond Bessel beams overcome many of the difficulties associated with Gaussian beams. We report on single shot processing of nanochannels with aspect ratio up to 100. Underlying physical phenomena are discussed.

Mineralized biological materials such as shells, skeleton, and teeth experience biomineralization. Biomimetic materials exploit the biomineralization process to form functional organic-inorganic hybrid nanostructures. In this work, we mimicked the biomineralization process by the de novo design of an amyloid-like peptide that self-assembles into nanofibers. Chemically active groups enhancing the affinity for metal ions were used to accumulate silicon and titanium precursors on the organic template. The self-assembly process and template effect were characterized by CD, FT-IR, UV-vis, fluorescence, rheology, TGA, SEM, and TEM. The self-assembled organic nanostructures were exploited as a template to form high-aspect-ratio 1-D silica and titania nanostructures by the addition of appropriate precursors. Herein, a new bottom-up approach was demonstrated to form silica and titania nanostructures that can yield wide opportunities to produce high-aspect-ratio inorganic nanostructures with high surface areas. The materials developed in this work have vast potential in the fields of catalysis and electronic materials. © 2011 American Chemical Society.