Microscale 3D Printing of Nanotwinned Copper

Continuous and Stable Printing Method of Planar Microstructure Based on Meniscus-Confined Electrodeposition

The meniscus-confined electrodeposition (MCED) technique offers advantages such as low cost and wide applicability, making it a promising method in the field of micro/nanofabrication. However, unstable meniscal morphology and poor deposition quality during planar deposition in MCED necessitate the development of improved methods. Therefore, a planar adaptive micro-tuning deposition method (PAMTDM), which utilizes the positioning technology of scanning electrochemical cell microscopy (SECCM) and employs a singular value decomposition (SVD) planar fitting method to determine the flatness of the deposition plane, is proposed. An adaptive micro-tuning motion mode was proposed by analyzing the variation patterns of the meniscus. Moreover, a combination of multi-physics finite element simulations and orthogonal experimental methods was introduced to determine the optimal motion parameters. The experimental results demonstrate that the PAMTDM effectively addresses the issues encountered during planar growth. Compared to the point-by-point deposition method, the PAMTDM achieves a threefold increase in deposition speed for continuous deposition of 105-μm-long line segments in two-dimensional planes, with a deposition current error of less than 0.2 nA. In conclusion, the proposed method provides significant insights into the broad future applications of MCED.

The Roles of Microprobe in Localized Electrodeposition: Electrolyte Localized Transport and Force-Displacement Sensitivity

Facing the rapid development of 6G communication, long-wave infrared metasurface and biomimetic microfluidics, the performance requirements for microsystems based on metal tiny structures are gradually increasing. As one of powerful methods for fabrication metal complex microstructures, localized electrochemical deposition microadditive manufacturing technology can fabricate copper metal micro overhanging structures without masks and supporting materials. In this study, the role of the microprobe cantilever (MC) in localized electrodeposition was studied. The MC can be used for precise deposition with electrolyte localized transport function and high accuracy force-displacement sensitivity. To prove this, the electrolyte flow was simulated when the MC was in bending or normal state. The simulation results can indicate the influence of turbulent flow on the electrolyte flow velocity and the pressure at the end of the pyramid. The results show that the internal flow velocity increased by 8.9% in the bending probe as compared with normal. Besides, this study analyzed the force-potential sensitivity characteristics of the MC. Using the deformation of the MC as an intermediate variable, the model of the probe tip displacement caused by the growth of the deposit and the voltage value displayed by the photodetector was mathematically established. In addition, the deposition of a single voxel was simulated by simulation process with the simulated height of 520 nm for one voxel, and the coincidence of simulation and experimental results was 93.1%. In conclusion, this method provides a new way for localized electrodeposition of complex microstructures.

Nanodroplet Flight Control in Electrohydrodynamic Redox 3D Printing

Electrohydrodynamic 3D printing is an additive manufacturing technique with enormous potential in plasmonics, microelectronics, and sensing applications thanks to its broad material palette, high voxel deposition rate, and compatibility with various substrates. However, the electric field used to deposit material is concentrated at the depositing structure, resulting in the focusing of the charged droplets and geometry-dependent landing positions, which complicates the fabrication of complex 3D shapes. The low level of concordance between the design and printout seriously impedes the development of electrohydrodynamic 3D printing and rationalizes the simplicity of the designs reported so far. In this work, we break the electric field centrosymmetry to study the resulting deviation in the flight trajectory of the droplets. Comparison of experimental outcomes with predictions of an FEM model provides new insights into the droplet characteristics and unveils how the product of droplet size and charge uniquely governs its kinematics. From these insights, we develop reliable predictions of the jet trajectory and allow the computation of optimized printing paths counterbalancing the electric field distortion, thereby enabling the fabrication of geometries with unprecedented complexity.

The Facile Three-Dimensional Printing of the Composite of Copper Nanosized Powder and Micron Powder with Enhanced Properties

Three-dimensional (3D) printing of Cu items is a new way to build up the structured Cu materials, but 3D printing of Cu items is usually a challenge because of the high melting point, high thermal conductivity, and high light reflection rate of Cu material. In this study, the composite of Cu microspheres powder and Cu nanoparticles (micro/nano Cu powder) is used to realize the 3D printing of Cu items with the selective laser melting technology. The sintering temperature and the thermal conductivity of micro/nano Cu powder are evidently decreased due to Cu nanoparticles' addition in the micron Cu powder. The results reveal that the 3D printing of 50%/50% micro/nano Cu powder needs laser power range of 100-240 W, which is in contrast to 200-340 W for 3D printing of 100% Cu microspheres powder. Furthermore, the conductivity, mechanical strength, and density of 3D-printed Cu items are improved with the addition of Cu nanoparticles into the micron Cu powder. The increasement of 34% on electrical conductivity and 17% on tensile strength are reached by the addition of 50% Cu nanoparticles with the laser power of 240 W.

Beginner's Guide to Micro- and Nanoscale Electrochemical Additive Manufacturing

Electrochemical additive manufacturing is an advanced microfabrication technology capable of producing features of almost unlimited geometrical complexity. A unique combination of the capacity to process conductive materials, design freedom, and micro- to nanoscale resolution offered by these electrochemical techniques promises tremendous opportunities for a multitude of future applications spanning microelectronics, sensing, robotics, and energy storage. This review aims to equip readers with the basic principles of electrochemical 3D printing at the small length scale. By describing the basic principles of electrochemical additive manufacturing technology and using the recent advances in the field, this beginner's guide illustrates how controlling the fundamental phenomena that underpin the print process can be used to vary dimensions, morphology, and microstructure of printed structures.

Microstructure-driven electrical conductivity optimization in additively manufactured microscale copper interconnects

As the microelectronics field pushes to increase device density through downscaling component dimensions, various novel micro- and nano-scale additive manufacturing technologies have emerged to expand the small scale design space. These techniques offer unprecedented freedom in designing 3D circuitry but have not yet delivered device-grade materials. To highlight the complex role of processing on the quality and microstructure of AM metals, we report the electrical properties of micrometer-scale copper interconnects fabricated by Fluid Force Microscopy (FluidFM) and Electrohydrodynamic-Redox Printing (EHD-RP). Using a thin film-based 4-terminal testing chip developed for the scope of this study, the electrical resistance of as-printed metals is directly related to print strategies and the specific morphological and microstructural features. Notably, the chip requires direct synthesis of conductive structures on an insulating substrate, which is shown for the first time in the case of FluidFM. Finally, we demonstrate the unique ability of EHD-RP to tune the materials resistivity by one order of magnitude solely through printing voltage. Through its novel electrical characterization approach, this study offers unique insight into the electrical properties of micro- and submicrometer-sized copper interconnects and steps towards a deeper understanding of micro AM metal properties for advanced electronics applications.

Targeted Additive Micromodulation of Grain Size in Nanocrystalline Copper Nanostructures by Electrohydrodynamic Redox 3D Printing

The control of materials' microstructure is both a necessity and an opportunity for micro/nanometer-scale additive manufacturing technologies. On the one hand, optimization of purity and defect density of printed metals is a prerequisite for their application in microfabrication. On the other hand, the additive approach to materials deposition with highest spatial resolution offers unique opportunities for the fabrication of materials with complex, 3D graded composition or microstructure. As a first step toward both-optimization of properties and site-specific tuning of microstructure-an overview of the wide range of microstructure accessed in pure copper (up to >99.9 at.%) by electrohydrodynamic redox 3D printing is presented, and on-the-fly modulation of grain size in copper with smallest segments ≈400 nm in length is shown. Control of microstructure and materials properties by in situ adjustment of the printing voltage is demonstrated by variation of grain size by one order of magnitude and corresponding compression strength by a factor of two. Based on transmission electron microscopy and atom probe tomography, it is suggested that the small grain size is a direct consequence of intermittent solvent drying at the growth interface at low printing voltages, while larger grains are enabled by the permanent presence of solvent at higher potentials.

In situ synthesis of hierarchically-assembled three-dimensional ZnS nanostructures and 3D printed visualization

Nanomaterials have gained enormous interest in improving the performance of energy harvest systems, biomedical devices, and high-strength composites. Many studies were performed fabricating more elaborate and heterogeneous nanostructures then the structures were characterized using TEM tomographic images, upgrading the fabrication technique. Despite the effort, intricate fabrication process, agglomeration characteristic, and non-uniform output were still limited to presenting the 3D panoramic views straightforwardly. Here we suggested in situ synthesis method to prepare complex and hierarchically-assembled nanostructures that consisted of ZnS nanowire core and nanoparticles under Ag₂S catalyst. We demonstrated that the vaporized Zn and S were solidified in different shapes of nanostructures with the temperatures solely. To our knowledge, this is the first demonstration of synthesizing heterogeneous nanostructures, consisting of a nanowire from the vapor-liquid-solid and then nanoparticles from the vapor-solid grown mechanism by in situ temperature control. The obtained hierarchically-assembled ZnS nanostructures were characterized by various TEM technologies, verifying the crystal growth mechanism. Lastly, electron tomography and 3D printing enabled the nanoscale structures to visualize with centimeter scales. The 3D printing from randomly fabricated nanomaterials is rarely performed to date. The collaborating work could offer a better opportunity to fabricate advanced and sophisticated nanostructures.

Visualizing Assembly Dynamics of All-Liquid 3D Architectures

To better exploit all-liquid 3D architectures, it is essential to understand dynamic processes that occur during printing one liquid in a second immiscible liquid. Here, the interfacial assembly and transition of 5,10,15,20-tetrakis(4-sulfonatophenyl) porphyrin (H₆ TPPS) over time provides an opportunity to monitor the interfacial behavior of nanoparticle surfactants (NPSs) during all-liquid printing. The formation of J-aggregates of H₄ TPPS^2- at the interface and the interfacial conversion of the J-aggregates of H₄ TPPS^2- to H-aggregates of H₂ TPPS^4- is demonstrated by interfacial rheology and in situ atomic force microscopy. Equally important are the chromogenic changes that are characteristic of the state of aggregation, where J-aggregates are green in color and H-aggregates are red in color. In all-liquid 3D printed structures, the conversion in the aggregate state with time is reflected in a spatially varying change in the color, providing a simple, direct means of assessing the aggregation state of the molecules and the mechanical properties of the assemblies, linking a macroscopic observable (color) to mechanical properties.

3D printing of multi-metallic microstructures by meniscus-confined electrodeposition

We studied a multi-metallic microscale 3D printing based on the meniscus-confined electrodeposition (MCED). The composition of Cu/Pt alloys can be controlled by applying different bias voltages to the CuSO4/H2PtCl4 mixed solution in MCED. We find that a double-barrel system had higher Cu/Pt alloy purity (maximum 100% Cu or maximum 80% Pt) than a single-barrel system. A Λ-shaped microstructure was printed to verify the capability to multi-metal microstructures in a single printing process.

A Review on Additive Manufacturing of Pure Copper

With the development of the aerospace and automotive industries, high heat exchange efficiency is a challenge facing the development of various industries. Pure copper has excellent mechanical and physical properties, especially high thermal conductivity and electrical conductivity. These excellent properties make pure copper the material of choice for the manufacture of heat exchangers and other electrical components. However, the traditional processing method is difficult to achieve the production of pure copper complex parts, so the production of pure copper parts through additive manufacturing has become a problem that must be overcome in industrial development. In this article, we not only reviewed the current status of research on the structural design and preparation of complex pure copper parts by researchers using selective laser melting (SLM), selective electron beam melting (SEBM) and binder jetting (BJ) in recent years, but also reviewed the forming, physical properties and mechanical aspects of pure copper parts prepared by different additive manufacturing methods. Finally, the development trend of additive manufacturing of pure copper parts is also prospected.

Interconnect Fabrication by Electroless Plating on 3D-Printed Electroplated Patterns

The metallic interconnects are essential components of energy devices such as fuel cells and electrolysis cells, batteries, as well as electronics and optoelectronic devices. In recent years, 3D printing processes have offered complementary routes to the conventional photolithography- and vacuum-based processes for interconnect fabrication. Among these methods, the confined electrodeposition (CED) process has enabled a great control over the microstructure of the printed metal, direct printing of high electrical conductivity (close to the bulk values) metals on flexible substrates without a need to sintering, printing alloys with controlled composition, printing functional metals for various applications including magnetic applications, and for in situ scanning electron microscope (SEM) nanomechanical experiments. However, the metal deposition rate (or the overall printing speed) of this process is reasonably slow because of the chemical nature of the process. Here, we propose using the CED process to print a single layer of a metallic trace as the seed layer for the subsequent selected-area electroless plating. By controlling the activation sites through printing by the CED process, we control, where the metal grows by electroless plating, and demonstrate the fabrication of complex thin-film patterns. Our results show that this combined process improves the processing time by more than 2 orders of magnitude compared to the layer-by-layer printing process by CED. Additionally, we obtained Cu and Ni films with an electrical resistivity as low as ∼1.3 and ∼2 times of the bulk Cu and Ni, respectively, without any thermal annealing. Furthermore, our quantitative experiments show that the obtained films exhibit mechanical properties close to the bulk metals with an excellent adhesion to the substrate. We demonstrate potential applications for radio frequency identification (RFID) tags, for complex printed circuit board patterns, and resistive sensors in a Petri dish for potential biological applications.

Epitaxial nanotwinned metals and alloys: synthesis-twin structure–property relations

Recent works of epitaxial nanotwinned metals and alloys with different stacking fault energies are reviewed to elaborate the relationship among synthesis conditions, intrinsic factors, twin structure and various properties.

Metals by Micro-Scale Additive Manufacturing: Comparison of Microstructure and Mechanical Properties

Many emerging applications in microscale engineering rely on the fabrication of 3D architectures in inorganic materials. Small-scale additive manufacturing (AM) aspires to provide flexible and facile access to these geometries. Yet, the synthesis of device-grade inorganic materials is still a key challenge toward the implementation of AM in microfabrication. Here, a comprehensive overview of the microstructural and mechanical properties of metals fabricated by most state-of-the-art AM methods that offer a spatial resolution ≤10 μm is presented. Standardized sets of samples are studied by cross-sectional electron microscopy, nanoindentation, and microcompression. It is shown that current microscale AM techniques synthesize metals with a wide range of microstructures and elastic and plastic properties, including materials of dense and crystalline microstructure with excellent mechanical properties that compare well to those of thin-film nanocrystalline materials. The large variation in materials' performance can be related to the individual microstructure, which in turn is coupled to the various physico-chemical principles exploited by the different printing methods. The study provides practical guidelines for users of small-scale additive methods and establishes a baseline for the future optimization of the properties of printed metallic objects-a significant step toward the potential establishment of AM techniques in microfabrication.

Direct-Write Printing Copper-Nickel (Cu/Ni) Alloy with Controlled Composition from a Single Electrolyte Using Co-Electrodeposition

Although various processes for metal printing at the micro- and mesoscale have been demonstrated, printing functional devices such as thermocouples, thermopiles, and heat flux sensors that function based on interfaces between an alloy and another alloy/metal demands processes for printing alloys. Furthermore, a high-quality and crystalline alloy is required for acceptable function of these devices. This article reports for the first time co-electrodeposition-based printing of single-phase solid solution nanocrystalline copper/nickel (Cu/Ni) alloy with various controllable compositions (Cu100Ni0 to Cu19Ni81) from a single electrolyte. The printed alloy is nanocrystalline (<35 nm), continuous, and dense with no apparent porosity, with remarkable mechanical and magnetic properties, without any postprocessing annealing such as heat treatment. In addition, a functional thermocouple fabricated using this process is demonstrated. Such a process can not only be used for fabrication of functional devices, it may also facilitate fundamental studies on alloys by printing a continuous library of alloy composition for material characterization.

A Low-Cost Electrochemical Metal 3D Printer Based on a Microfluidic System for Printing Mesoscale Objects

For the additive manufacturing (AM) of metal objects, the powder-based fusion (PBF) method is routinely utilized to fabricate macroscale parts. On the other hand, electrochemical additive manufacturing (ECAM), in which metallic structures are deposited through the electrochemical reduction of metal ions, is a promising technique for producing micro- and nanoscale objects. However, a gap exists in terms of fabricating mesoscale objects within the current AM techniques. The PBF method is limited by fabrication precision due to pronounced residual stresses, and most current ECAM systems are difficult to scale up to print mesoscale objects. In the present paper, the novel design of a low-cost ECAM 3D printer based on a microfluidic system is proposed for fabricating mesoscale metal parts. The meniscus-guided electrodeposition approach is utilized, in which a meniscus is formed between the print head and substrate, and electrodeposition is confined within the meniscus. A 3D object is fabricated by the meniscus moving with the print head according to the programmed pattern and the material subsequently being deposited at the designated locations. The key to the proposed design is to maintain a mesoscale meniscus, which normally cannot be sustained by the electrolyte surface tension with a print nozzle having a mesoscale diameter. Therefore, a microfluidic system, called the fountain pen feed system, constituting a semi-open main channel and comb structure, was designed to maintain a mesoscale meniscus throughout the printing process. Two materials, copper and nickel, with various geometric shapes were attempted to print by the proposed ECAM system, and, during the printing process, both fluid leaking and meniscus breaking were completely prevented. Free standing tilted copper pillars with controlled angles were printed to show the ability of the proposed design in fabricating 3D structures. A copper circuit was also printed on a non-conductive substrate to demonstrate a possible application of the proposed ECAM system in the fabrication of functional electronics.

Additive printing of pure nanocrystalline nickel thin films using room environment electroplating

Given its high temperature stability, oxidation-, corrosion- and wear-resistance, and ferromagnetic properties, Nickel (Ni) is one of the most technologically important metals. This article reports that pure and nanocrystalline (Ni) films with excellent mechanical and magnetic properties can be additively printed at room environment without any high-temperature post-processing. The printing process is based on a nozzle-based electrochemical deposition from the classical Watt's bath. The printed Ni film showed a preferred (220) and (111) texture based on x-ray diffraction spectra. The printed Ni film had close to bulk electrical conductivity; its indentation elastic modulus and hardness was measured to be 203 ± 6.7 GPa and 6.27 ± 0.34 GPa, respectively. Magnetoresistance, magnetic hysteresis loop, and magnetic domain imaging showed promising results of the printed Ni for functional applications.

A Hybrid Process for Printing Pure and High Conductivity Nanocrystalline Copper and Nickel on Flexible Polymeric Substrates

Printing functional devices on flexible substrates requires printing of high conductivity metallic patterns. To prevent deformation and damage of the polymeric substrate, the processing (printing) and post-processing (annealing) temperature of the metal patterns must be lower than the glass transition temperature of the substrate. Here, a hybrid process including deposition of a sacrificial blanket thin film, followed by room environment nozzle-based electrodeposition, and subsequent etching of the blanket film is demonstrated to print pure and nanocrystalline metallic (Ni and Cu) patterns on flexible substrates (PI and PET). Microscopy and spectroscopy showed that the printed metal is nanocrystalline, solid with no porosity and with low impurities. Electrical resistivity close to the bulk (~2-time) was obtained without any thermal annealing. Mechanical characterization confirmed excellent cyclic strength of the deposited metal, with limited degradation under high cyclic flexure. Several devices including radio frequency identification (RFID) tag, heater, strain gauge, and temperature sensor are demonstrated.

Microtopography-Guided Radial Gradient Circle Array Film with Nanoscale Resolution

Distribution of multimaterials at arbitrary positions with nanoscale resolution and over a large area substrate is essential to future advances in functional graded materials. Such stringent requirements are highly beyond the reach of current techniques, although newly developed 3D printing technologies are addressed. Here, a radial gradient circle array film with the distribution accuracy up to ≈18 nm is fabricated by using microtopographic substrate. A mathematical model is developed to guide the distribution of position, size, shape, and type of materials on an arbitrary section for the given morphology of substrate. The periodic electrical and mechanical properties of the radial gradient circle film are identified, which can be beneficial for further functionalization and applications, such as gradient refractive index lenses, microcoils, and microantennas.

Activated Carbon in the Third Dimension-3D Printing of a Tuned Porous Carbon

A method for obtaining hierarchically structured porous carbons, employing 3D printing to control the structure down to the lower µm scale, is presented. To successfully 3D print a polymer precursor and transfer it to a highly stable and structurally conformal carbon material, stereolithography 3D printing and photoinduced copolymerization of pentaerythritol tetraacrylate and divinylbenzene are employed. Mechanically stable structures result and a resolution of ≈15 µm is demonstrated. This approach can be combined with liquid porogen templating to control the amount and size (up to ≈100 nm) of transport pores in the final carbonaceous material. Additional CO2 activation enables high surface area materials (up to 2200 m2 g-1) that show the 3D printing controlled µm structure and nm sized transport pores. This unique flexibility holds promise for the identification of optimal carbonaceous structures for energy application, catalysis, and adsorption.

3D Printing of Highly Pure Copper

Copper has been widely used in many applications due to its outstanding properties such as malleability, high corrosion resistance, and excellent electrical and thermal conductivities. While 3D printing can offer many advantages from layer-by-layer fabrication, the 3D printing of highly pure copper is still challenging due to the thermal issues caused by copper’s high conductivity. This paper presents a comprehensive review of recent work on 3D printing technology of highly pure copper over the past few years. The advantages and current issues of 3D printing methods are compared while different properties of copper parts printed by these methods are summarized. Finally, we provide several potential applications of the 3D printed copper parts and an overview of current developments that could lead to new improvements in this advanced manufacturing field.

Multi-metal electrohydrodynamic redox 3D printing at the submicron scale

An extensive range of metals can be dissolved and re-deposited in liquid solvents using electrochemistry. We harness this concept for additive manufacturing, demonstrating the focused electrohydrodynamic ejection of metal ions dissolved from sacrificial anodes and their subsequent reduction to elemental metals on the substrate. This technique, termed electrohydrodynamic redox printing (EHD-RP), enables the direct, ink-free fabrication of polycrystalline multi-metal 3D structures without the need for post-print processing. On-the-fly switching and mixing of two metals printed from a single multichannel nozzle facilitates a chemical feature size of <400 nm with a spatial resolution of 250 nm at printing speeds of up to 10 voxels per second. As shown, the additive control of the chemical architecture of materials provided by EHD-RP unlocks the synthesis of 3D bi-metal structures with programmed local properties and opens new avenues for the direct fabrication of chemically architected materials and devices.

Advanced Materials for Next-Generation Spacecraft

Spacecraft are expected to traverse enormous distances over long periods of time without an opportunity for maintenance, re-fueling, or repair, and, for interplanetary probes, no on-board crew to actively control the spacecraft configuration or flight path. Nevertheless, space technology has reached the stage when mining of space resources, space travel, and even colonization of other celestial bodies such as Mars and the Moon are being seriously considered. These ambitious aims call for spacecraft capable of self-controlled, self-adapting, and self-healing behavior. It is a tough challenge to address using traditional materials and approaches for their assembly. True interplanetary advances may only be attained using novel self-assembled and self-healing materials, which would allow for realization of next-generation spacecraft, where the concepts of adaptation and healing are at the core of every level of spacecraft design. Herein, recent achievements are captured and future directions in materials-driven development of space technology outlined.

Dynamic "Scanning-Mode" Meniscus Confined Electrodepositing and Micropatterning of Individually Addressable Ultraconductive Copper Line Arrays

Micro- and nanopatterning of cost-effective addressable metallic nanostructures has been a long endeavor in terms of both scientific understanding and industrial needs. Herein, a simple and efficient dynamic meniscus-confined electrodeposition (MCED) technique for precisely positioned copper line micropatterns with superior electrical conductivity (greater than 1.57 × 10⁴ S/cm) on glass, silicon, and gold substrates is reported. An unexpected higher printing speed in the evaporative regime is realized for precisely positioned copper lines patterns with uniform width and height under horizontal scanning-mode. The final line height and width depend on the typical behavior of traditional flow coating process, while the surface morphologies and roughness are mainly governed by evaporation-driven electrocrystallization dynamics near the receding moving contact line. Integrated 3D structures and a rapid prototyping of 3D hot-wire anemometer are further demonstrated, which is very important for the freedom integration applications in advanced conceptual devices, such as miniaturized electronics and biomedical sensors and actuators.