3D Micro Research Articles

Ni–Zn hydroxide-based bi-phase multiscale porous nanohybrids: physico-chemical properties

In this investigation, we report the synthesis of novel homogeneous micro–mesoporous bi-phase nanohybrids based on Ni/Zn hydroxides using a simple and low-cost free-template urea-based hydrothermal process at two different growth temperatures (120 and 180 °C) for 6 h in two cases of precursor ratios (Ni:Zn = 1:1 and Ni:Zn = 1:2). The synthesized products have been characterized with different techniques such as XRD, FT-IR, FESEM, Raman, BET and XPS analysis to identify quantitatively and qualitatively their original physico-chemical properties. The obtained structural results show the formation of bi-hydroxide-based products: α*-Ni(OH)2·0.75 H2O with Zn5(CO3)2(OH)6 (case Ni:Zn = 1:1) or with Zn4(CO3)(OH)6·H2O (Ni:Zn = 1:2) which are also proven by FTIR and Raman analyses. However, the obtained 3D micro–meso-nanohybrids with different pore morphology have been demonstrated through the FESEM micrographs depending on the synthesis conditions. Moreover, these porous products have been subjected to textural studies with the BET results showcasing a porous morphology with a reasonable specific surface area (SSA) and pore volume in the range (70–150 m2/g) and (0.19–0.85 cm3/g), respectively. Also, a clear improvement in the BET SSA (two times the initial value) was obtained with increasing the growth temperature in the two cases (1:1 and 1:2). Consequently, we have successfully synthesized active mesoporous materials with interesting specific surface area and porosity (pore volume and size) which make them attractive materials for electrode applications especially in energy storage and biosensing.

Three-dimensional microsupercapacitors based on interdigitated patterns of interconnected nanowire networks

There is a proliferation of autonomous microscale devices, which are increasingly in need of power sources of commensurate form factors. The trade-off between the areal energy and power capabilities of miniature energy storage devices restrict their abilities to meet the requirements of these microscale devices. However, three-dimensional (3D) micro- and nanoarchitectures have the potential to meet the energy requirements of autonomous microscale devices, while retaining the power capabilities of thin-film systems. In this paper, we present a novel full-cell architecture and fabrication strategy for 3D microscale energy storage devices based on template-assisted electrodeposition of three-dimensionally interconnected metallic nanowire network, and its subsequent laser-patterning to form interdigitated nanostructured electrodes. The patterned nanowire networks are functionalized with the polyaniline active electrode material via an electroless deposition procedure. We show that a footprint areal capacitance/energy enhancement of more than 5 times is achieved by just 10 μm-high nanowire networks, in addition to enhanced power capabilities.

Joint structural and electrochemical modeling: Impact of porosity on lithium-ion battery performance

Future increases of energy density of lithium-ion batteries require a systematic optimization of electrode structure and the related production process. Such optimization is facilitated by electrochemical models which predict cell performance with good accuracy. In this work, classic relations of structure to model parameters in the classical Doyle-Newman electrode model are replaced to improve the prediction accuracy of the model regarding electrode structure effects. Therefor, a 3D micro structure model is used to derive effective electrode property relations for ionic and electric conductivity, which are then used in the computationally efficient P2D framework of the Doyle-Newman model. Simulations show clearly the transition from an electron transport limited to an ion transport limited electrode performance with increasing compression ratio. Integrating the derived algebraic structure-model parameter relations into the electrochemical model allows a higher accuracy in predicting the optimal porosity of the experimental data compared to the classical P2D model.

Benzoic acid-assisted substrate-free synthesis of ultrathin nanosheets assembled two-dimensional porous Co3O4 thin sheets with 3D hierarchical micro-/nano-structures and enhanced performance as battery-type materials for supercapacitors

Two-dimensional (2D) porous materials have been proved to be meritorious for supercapacitors (SCs) due to unique properties of large surface area, superior intrinsic porosity and high electrical conductivity. In this work, we reported for the first synthesis of 2D porous Co3O4 thin sheets assembled by ultrathin nanosheets via direct hydrothermal decomposition of aqueous solution of cobalt nitrate in the presence of benzoic acid (BA) without any template or surfactant. High specific capacity (497, 598.5 and 399 C g−1 at 1.0 A g−1) and remarkable cycling stability (9.8, 6.3 and 13.1% loss over 8000 cycles at 10.0 A g−1) were achieved in a three-electrode system for the Co3O4 thin sheets at 200 °C for 6, 12 and 24 h with different specific surface area of 69.96, 142.15 and 42.07 m2 g−1, which can be attributed to the special structural feature of an open and porous surface layer and the synergistic effect of 2D and 3D structure that significantly facilitates fast electron transport, ion diffusion and intimate electrode/electrolyte contact. Furthermore, an assembled asymmetric supercapacitor (ASC, Co3O4 thin sheets//activated carbon (AC)) can reach a working output potential difference of 0–1.6 V with a maximum energy density of 22.49 Wh·kg−1 at the power density of 800 W kg−1 with excellent cyclic stability (only 8.2% loss of its initial specific capacity value over 10000 cycles). The results show that our synthesis provides a new insight into the fabrication of 2D hierarchical porous Co3O4 thin sheets; in addition, the as-synthesized Co3O4 thin sheets have potential for various applications in SCs, electrochemical sensing, and lithium ion battery.

Intrinsic stress-induced bending as a platform technology for controlled self-assembly of high-Q on-chip RF inductors

This work reports on the modelling and process technology development for the design and fabrication of vertical, 3D, monolithic RF-MEMS inductors based on self-assembly via intrinsic stresses otherwise referred to as residual or internal stresses in thin films. Stress-induced bending in different cantilever designs were modelled at various film thicknesses using finite element analysis method and bending conditions were optimized. Intrinsic stress-induced bending mechanism is verified by fabrication of bi-layer metallic micro cantilever structures with varying stress conditions which reach bending angles of up to 137° and possibly more upon release. By modulating the loading mode (tensile or compressive) along the beam length, complex out-of-plane wavy cantilevers with multiple upward and/or downward bends were realized. The fabrication and modelling results display large overlap which further demonstrates the applicability of intrinsic stress-induced bending as a controllable technology towards fabrication of out-of-plane 3D micro components. Additionally, as a potential application to RF-MEMS inductors, stress-induced self-assembly of patterned thin film stacks into out-of-plane inductor topologies of varying geometries was investigated. Electromagnetic modelling tools were used to study the effect of bending on inductor performance (primarily the Q factor and self-resonance frequency—f SR), and results were evaluated by comparison to planar inductors of the same number of turns and dimensions, which revealed Q factor and f SR improvement of more than 100% upon bending away from substrate surface.

3D Micro Porous Cobalt−Iron−Phosphorus Electrocatalyst for Overall Water Splitting

3D Co-Fe-P microstructure based on electrodeposition was synthesized for high performance oxygen and hydrogen evolution reaction catalysts. Preferentially, Fe/Co ratio of Co-Fe-P film was optimized to 1.1 and exhibited the highest activity for the oxygen evolution. It is related with the transfer of the valence electron from Co to Fe and P. Based on these characteristics and Cu foam microstructure, 3D porous Co-Fe-P foam was fabricated. The Co-Fe-P foam had 94 times larger electrochemical active surface area (ECSA) than the Co-Fe-P film with similar Fe/Co ratios of 1.1, resulting in a high activity for the oxygen evolution reaction (294 mV at 10 mA/cm2) and hydrogen evolution reaction (73 mV at 10 mA/cm2) in 1 M KOH solution. The electrodeposited Co-Fe-P foam itself can be directly used without binder, and microstructure of the electrode can be engineered by controlling the electrodeposition condition, leading to the enlarged ECSA and improved performance. This study offers a facile and controllable synthesis of catalyst and electrode through an easy electrodeposition process.

A special process of 3D servo scanning micro electro discharge machining for machining pierced micro structures of NiTi alloy tube

Although nickel–titanium (NiTi) alloys have many excellent material properties, micro structures of NiTi alloys are rarely machined by conventional mechanical machining due to its high elasticity and severe tool wear. A micro tube as an active catheter with typical driving structures made from a NiTi shape memory alloy (SMA) is a key part in an interventional micro robot system. The driving structures, as complex 3D micro structures pierced through the thin-walled micro tube, are mainly fabricated by a lithography-based process at present. However, not only is the process inefficient and costly, but its etching depth is also limited. In this research, a novel process of 3D servo scanning micro electro discharge machining (EDM) with the movement of two-axis linkage and one-axis servo is proposed for efficiently machining 3D micro structures. The processing procedures are presented, including 3D model design, scanning paths planning, 3D NC codes generation and 3D micro EDM. The emphasis is focused on the methods for planning the scanning paths and generating the CNC codes considering the special 3D micro structures. By using the planned complementary scanning paths, the processing stability is improved for successfully machining the typical driving structures within 5 h. The machining experiments verify the feasibility of the proposed process and related methods.

Permeability upscaling in complex carbonate samples using textures of micro-computed tomography images

ABSTRACT Developing a better characterization of fluid flow properties in carbonate reservoirs is a critical step for enhanced oil recovery applications in the oil industry. Indeed, carbonate reservoirs rocks are in general highly heterogeneous with variability revealed from submicron to centimeters. In several studies, Digital Rock Physics (DRP) was implemented as a technique which aims to help characterizing rock properties behavior at pore scale. This approach uses 3D X-ray micro tomography images to characterize pore network and also simulate rock properties from these images. Even though DRP is able to predict realistic rock properties in sandstone reservoirs it is still suffering from a lack of clear workflow in carbonate rocks. The main challenge is the upscaling of simulated properties from fine to coarse. In this paper, we propose a new upscaling method to characterize absolute permeability in carbonate core plugs samples using textures of Micro-Computed Tomography images. We propose to classify 3D micro-CT images of rock samples in terms of textures and predict the overall rock permeability. Finally, we discuss the advantages and limitations of this new approach. Overall the present work proposes an efficient and faster alternative DRP workflow for upscaling from pore-scale to core-scale.

Numerical simulation of creep fracture with internal time-dependent hyperelastic-Kelvin cohesive bonds

The macro brittle creep is closely related to the fracturing process on the micro scale. The virtual internal bond (VIB) is a microstructure-based continuum modeling method. It considers a solid as a bond network on the micro scale. The macro constitutive relation is directly derived from the micro bond potential, which intrinsically contains the micro fracture mechanisms. In this study, the VIB is firstly extended for modeling viscoelasticity, and then it is applied to creep fracture simulation. To reflect the time-dependence property of creep, a viscous bond is introduced to join a time-dependent hyperelastic bond in parallel to constitute a hybrid hyperelastic-Kelvin bond. Based on the hybrid bond potential, the macro viscohyperelastic constitutive relation is derived. The corresponding relationship between the micro bond parameters and the macro material constants is theoretically calibrated. Through this model, the typical three-stage feature of the brittle creep is well reproduced and the creep fracture is effectively simulated. The simulation results suggest that the fast and unstable fracture growth leads to the tertiary stage of creep. The viscosity mainly affects the deformation rate in the primary and tertiary stage of creep. The constitutive relation of the VIB stems from the 1D micro bond; thus, the rheology model derived from the cluster of rheological elements (e.g., spring, dashpot) is easily incorporated into the VIB framework, avoiding the 1D-to-3D generalization of the rheology law. For both the micro viscosity and fracture mechanisms that are incorporated into the macro constitutive relation, the present VIB can simulate complex creep fractures without a separate fracture criterion. It has great potential to simulate fracture propagation in a more extensive viscohyperelastic material.

Influence of hot water treatment during laser ablation in liquid on the shape of PbO nanoparticles

The significant role of the unavoidable hot water treatment during laser ablation of lead in water in formation of the nonspherical 2D (plates) and 3D micro- and nanoparticles (octahedra and rods) in suspension and at the target surface has been shown experimentally. The formation of the nonspherical particles has been demonstrated at hot water treatment alone at temperature above 70 °C achieved frequently during laser ablation in water. The simple model was applied for explanation of the obtained formation of 3D particles. The 2D plates formed by seedless growth. The influence of the unavoidable hot water treatment should be considered as an additional mechanism for explanation of the formation of the nonspherical nanoparticles during laser ablation in water.

Mechanical characterizations of single-crystalline (Cu, Ni)6Sn5 through uniaxial micro-compression

Microelectronic industry is experiencing a major paradigm shift from the conventional two-dimensional into hierarchical three-dimensional integrated circuits (3D ICs). In 3D IC technology, through-silicon-vias and micro joints are regarded as the two vital interconnection processes to achieve higher packing density as well as heterogeneous integration. However, the miniaturization of solder joints down to micron level causes the consequence that intermetallic compounds takes up most of the volume of micro joints within a short period of time, in stark contrast to the well-known scenario at the opposite end of spectrum that soft Sn-based solders always occupies a high volume fraction of joints. Thus, intermetallics are expected to shoulder primary responsibilities of mechanical reliability in micro joints. Therefore, a full understanding about the mechanical behaviors of intermetallics at micron scale is essential for validity and reliability evaluation of 3D IC interconnections. The present study focuses on mechanical assessment of single-crystalline (Cu, Ni)6Sn5 by means of uniaxial micro-compression and nanoindentation. The anisotropic mechanical properties of hexagonal Cu6Sn5 are investigated by compression testing on single-crystalline Cu6Sn5 micropillars with different grain orientations. The jammed network of dislocation inside deformed micropillars suggests that intermittent strain bursts in stress-strain curves are relevant to dislocation-avalanche mechanism. In addition, Cu6Sn5 micropillars are found to exhibit brittle cleavage failure with most fractured pieces crushed in the same direction, and one set of preferred cleavage plane are characterized by post-mortem analysis. Moreover, the strengthening and phase-stabilizing effect of Ni element on Cu6Sn5 is also investigated by micropillar compression and X-ray diffraction, respectively.

Electrokinetically Controlled Asymmetric Ion Transport through 1D/2D Nanofluidic Heterojunctions

AbstractSupported 2D layered materials are widely used in gas separation, water treatment, energy conversion, etc. In conventional viewpoint, the atop 2D membrane functions as an active layer for mass or charge separation in vapor or liquid phase, while the substrate membrane, containing aligned or tortuous 1D micro or nanoscaled fluidic channels, functions as a mechanical support. However, asymmetric transport property induced by the mixed‐dimensional composite structure is an equally very important, yet long‐overlooked element that endows new features to the membrane‐scale nanofluidic systems and contributes to the promotion of overall performance. Here, reported are asymmetric ion transport properties through 1D/2D nanofluidic heterojunction membrane (NFHM) under three different types of electrokinetic driving force. The 1D/2D NFHM comprises of self‐assembled graphene oxide multi‐layers (2DM, negatively charged) supported on a polydopamine‐coated 1D nanopore array (1DM, ampholytic). Intriguingly, it is found that the preferential direction for electric‐field‐driven ionic transport is from the 2DM to the 1DM, while under the concentration difference or the hydraulic flow, the preferred direction for diffusion or streaming ionic current goes in the reversed direction, from the 1DM to the 2DM. A theoretical model based on coupled Poisson–Nernst–Planck and Navier–Stokes equations is employed to explain the asymmetric ion transport phenomena.

An innovative micro magnetic separator based on 3D micro-copper-coil exciting soft magnetic tips and FeNi wires for bio-target sorting

Manipulation of cells or bio-targets is required in a variety of biological, diagnostic and therapeutic applications. In this paper, we present a novel magnetic separator for magnetic bead labeled-target sorting in microfluidic systems. This micro magnetic separator includes 3D micro copper coil, soft magnetic tips and FeNi wires. The magnetic tips and FeNi wires are first simulated and optimized by MagNet software to increase the magnetic force exerted on magnetic beads, and fabricated by microfabrication technology. The experiment results show the sorting ratio of the magnetic beads can be up to 92.5% with the current of 200 mA and the flow rate of 5 µL/min. The maximum sorting ratio can reach 78.4% for 100 CFU/mL E. coli O157:H7 sample with the current of 200 mA and the flow rate of 0.5 µL/min. On account of the miniaturization, high sorting efficiency, low excitation current, high level of detection automation and easy integration with micro magnetic sensor, this micro magnetic separation system can be a potential application in bio-target sorting and detecting.

Wear behavior of TiAlN coated WC tool during micro end milling of Ti-6Al-4V and analysis of surface roughness

The demand for high quality micro components has been on the upsurge for the past few decades. Nowadays micro end milling is preferred to produce 3D micro parts. This paper presents an investigation on wear behavior of solid tungsten carbide (WC) tool with TiAlN coating during micro end milling of Ti-6Al-4V. Miniaturization of the tool combined with machining of hard to machine material like Ti-6Al-4V results in rapid tool wear. Feed/tooth to tool edge radius ratio (f/r) has got significant influence on micro end milling machining mechanism. For f/r less than one, ploughing is dominant, and the shearing mechanism prevails when f/r is greater than one. Therefore, experiments were carried out at two feed rates 0.3 µm/tooth and 5 µm/tooth to examine the effect of tool edge radius on tool wear. Tool wear in terms of flank wear, adhesive wear, abrasive wear, enlargement of tool edge radius, and delamination of coating was studied, and an investigation on the effect of tool wear on surface roughness was also carried out. A 3D optical profilometer was used to characterize tool wear and surface finish of the machined feature. With 0.3 µm/tooth feed rate, tool fails after ~700 mm length of cut and with 5 µm/tooth feed rate, tool fails after ~1000 mm length of cut. For both 0.3 µm/tooth and 5 µm/tooth feed rates tool fail approximately at 15–20 µm flank wear width. Adhesive wear was found to be the major tool failure mechanism for both feed rates. Moreover, in micro end milling operation selecting a feed rate slightly above the tool cutting edge radius will be beneficial so that a good surface finish is obtained during initial stages of the wear.

DigiCoal: A computational package for characterisation of coal cores

Coal cores contain a complex fracture system, known as cleats, that highly impacts its petrophysical properties. We present, DigiCoal computational toolbox, an integrated set of numerical functions, for analysing 3D micro computed tomography (micro-CT) images of coal and reconstructing representative digital models. The method presented in this paper can be applied to other fractured rocks as well. Coal characteristics analysed in this paper include cleat geometry, topology of cleat network, degree of mineralisation, and roughness of cleat surfaces. Micro-CT scanning procedures to obtain high-quality 3D images of coal are explained. Then, the steps to computationally analyse the images are described: CT image pre-processing, statistics extraction, digital coal modelling and structural analyses. This paper offers an overview of the structure and techniques used in the creation of the computational methods, together with code snippets and applications.

Electroless Deposition-Assisted 3D Printing of Micro Circuitries for Structural Electronics.

Three-dimensional (3D) printing is a next-generation free-form manufacturing technology for structural electronics. The realization of structural electronic devices necessitates the direct integration of electronic circuits into 3D objects. However, creating highly conductive, high-resolution patterns in 3D remains a major challenge. Here, we report on a metallic 3D printing method that incorporates electroless deposition (ELD) into the direct ink writing method. Our approach consists of two steps: (1) direct ink writing of catalyst microstructures with a functional catalyst ink containing Ag ions and (2) ELD of Cu onto the printed catalyst structures. High-quality, stable Cu 3D printing is achieved through the design of the Ag catalyst ink; hydroxypropyl cellulose is added as both a rheological modifier (printing) and dissolution inhibitor (ELD). As a result, various two-dimensional (2D) and 3D Cu micro circuitries with high conductivity (∼65% of bulk) can be directly integrated onto 3D plastic substrates without the need for high-temperature annealing. A hybrid strategy that combines ELD-assisted 3D printing and conventional fused deposition modeling enables full fabrication of structural electronic devices. This 3D printing strategy can be a low-cost and facile method for obtaining highly conductive metallic 2D and 3D microstructures in structural electronics.

Focused ion beam based nano-kirigami/origami for three-dimensional micro/nanomanufacturing and photonic applications

<sec>High-resolution three-dimensional (3D) micro-/nano-fabrication techniques form an important basis for developing the modern micro-/nano-photonics. In this paper, we systematically introduce a new 3D micro-/nano-fabrication technique named as nano-kirigami, which is based on the focused ion beam (FIB) induced in-situ “cutting” and “folding” of a suspended gold film. The high-dose FIB milling fulfils the “cutting” process, and the low-dose FIB irradiation of the effective sample area acts as a mean of “folding”, well representing the fabrication principle of macro-kirigami. By utilizing the topography-guided stress equilibrium during FIB irradiation, nano-kirigami can reliably achieve rich 3D shape transformations, such as multi-directional folding, bending, buckling and twisting, with resolution down to below 50 nm. Taking the FIB-induced stress as a stimulus, the FIB-based nano-kirigami can be divided into “tree-type” and “closed-loop” fabrication from the perspective of topological classifications in multibody dynamics. The characteristics, advantages and disadvantages between the two different types of processes are analyzed and summarized in the paper.</sec><sec>The rich 3D shape deformation characteristics bring about unimaginable possibilities for the fabrication of various novel 3D structures, and the generation of new geometries facilitates the exploration of new physics. For example, by taking advantage of the 3D plasmonic conductive couplings, the composite symmetry-broken SRR-based configuration is constructed for the efficient generation of significant chiral Fano resonances. Moreover, with the close-loop nano-kirigami induced by FIB global irradiation, the giant intrinsic optical chirality is achieved in a 3D pinwheel-like structure with exotic twisting and rotation geometric features. Especially, the rotation of the linear polarization direction, caused by the circular birefringence, reaches an efficiency of 310000°/mm which exceeds the reported value of chiral metamaterial and congeneric two-dimensional planar nanostructure. Another example is the metasurface formed by alternately arranging the left-handed pinwheel structure and right-handed pinwheel structure in the horizontal plane, which can diffract cross-polarized transmitted light efficiently while clear photon spin Hall effect is observed.</sec><sec>The introduced nano-kirigami technique, as well as the generated exotic 3D nanostructures and their photonic applications, can build up a novel 3D miro-/nano-fabrication platform for versatile structural geometries with promising functionalities, which may find great potential applications in areas such as micro-/nano-photonics, electronic and magnetic devices, plasmonics, optomechanics, micro-/nano-electromechanical systems, etc.</sec>

3D highly efficient photonic micro concave-pit arrays for enhanced solar water splitting.

The construction of three-dimensional (3D) photonic micro/nanostructures is regarded as one of the most promising approaches to develop highly efficient photoelectrodes for solar water splitting. Here, we report the design and fabrication of an indium tin oxide glass with 3D micro concave-pit arrays (MCPAs) as an effective photonic substrate for dramatically enhanced photoelectrochemical (PEC) water splitting. Compared with the planar counterpart, more than three-fold photocurrent density can be obtained for the 3D photoelectrodes with In2S3 nanosheet arrays grown on the inner surfaces of the MCPAs, mainly ascribable to their largely improved light trapping ability and increased surface area for charge separation and extraction. The PEC performance is further elevated by constructing an effective In2S3/ZnO heterojunction to accelerate the photocarrier separation. As a result, the 3D MCPA-based photoanodes demonstrate a maximum incident photon to current efficiency of 11.7% at 380 nm, which is about four times higher than that of the planar counterpart. The significant advancement demonstrated here provides a facile and low-cost route for the large-scale fabrication of 3D photonic electrodes aiming to achieve highly efficient PEC water splitting.

3D printing methods for micro- and nanostructures

The physical and physicochemical fundamentals of three-dimensional (3D) micro- and nanoprinting are presented. 3D printing (or additive manufacturing technology) is a process which fabricates structures and devices by depositing material (usually layer by layer) according to a 3D digital model. The methods and results reviewed here are limited to those from micro- and nanoscale fields, which are in demand in the fields of electronics, photonics, and bionics. Special attention is given to methods for fabricating sub-100-nm structures, including single- and two-photon polymerization stereolithography, electrohydrodynamic inkjet printing, and laser-induced forward transfer. The advantages and disadvantages of 3D printing methods are discussed, together with prospects for their development and application.

Reverse micro EDMed 3D hemispherical protruded micro feature: microstructural and mechanical characterization

3D hemispherical protruded micro features find wide application in various fields of surface engineering viz. micro lens let arrays, solar cells, energy conversion devices, heat transfer applications, tribological applications and many more. The present authors have already devised a technique for generating 3D hemispherical protruded micro feature by suitable tool modification in reverse micro EDM. In this paper, the microstructural and mechanical characterization of the already generated 3D hemispherical protruded micro feature is studied in order to determine the extent of the formed recast layer, heat affected zone (HAZ) and their mechanical properties viz. hardness, elastic modulus and residual stress in comparison to the parent material. Results indicate that the recast layer has higher hardness and elastic modulus followed by the hardened layer of HAZ as compared to the parent material. The soft layer of HAZ has the least hardness and elastic modulus. Qualitative analysis of residual stress using the loading and unloading portion of the load-displacement curves indicate that the recast layer has compressive residual stresses while the soft layer of HAZ has tensile residual stresses.