Low Melting Temperature Metal Research Articles

Hypoeutectic Liquid Metal Printing of 2D Indium Gallium Oxide Transistors.

2D native surface oxides formed on low melting temperature metals such as indium and gallium offer unique opportunities for fabricating high-performance flexible electronics and optoelectronics based on a new class of liquid metal printing (LMP). An inherent property of these Cabrera-Mott 2D oxides is their suboxide nature (e.g., In2O3-x), which leads high mobility LMP semiconductors to exhibit high electron concentrations (ne >1019cm-3) limiting electrostatic control. Binary alloying of the molten precursor can produce doped, ternary metal oxides such as In-X-O with enhanced electronic performance and greater bias-stress stability, though this approach demands a deeper understanding of the native oxides of alloys. This work presents an approach for hypoeutectic rapid LMP of crystalline InGaOx (IGO) at ultralow process temperatures (180°C) beyond the state of the art to fabricate transistors with 10X steeper subthreshold slope and high mobility (≈18cm2Vs-1). Detailed characterization of IGO crystallinity, composition, and morphology, as well as measurements of its electronic density of states (DOS), show the impact of Ga-doping and reveal the limits of doping induced amorphization from hypoeutectic precursors. The ultralow process temperatures and compatibility with high-k Al2O3 dielectrics shown here indicate potential for 2D IGO to drive low-power flexible transparent electronics.

Achieving low-temperature wafer level bonding with Cu-Sn-In ternary at 150 °C

In this work, a low-temperature wafer-level bonding process at 150 °C was carried out on Si wafers containing 10 µm-sized microbumps based on the Cu-Sn-In ternary system. Thermodynamic study shows that addition of In enables low-melting temperature metals to reach liquid phase below In melting point (157 °C) and promotes rapid solidification of the intermetallic layer, which are beneficial for achieving low-temperature bonding. Microstructural observation shows high bonding quality with low amount of defect. SEM and TEM characterization concludes that a single-phase intermetallic formed in the bond and identified as Cu6(Sn,In)5 with a hexagonal lattice. Mechanical tensile test indicates that the bond has a mechanical tensile strength of 30 MPa, which are adequate for 3D heterogeneous integration.

Ultrasonic Characterization of Porosity in Components Made by Binder Jet Additive Manufacturing

Binder jet metallic additive manufacturing (AM) is a popular alternative to powder bed fusion and directed energy deposition because of lower costs, elimination of thermal cycling, and lower energy consumption. However, like other metallic AM processes, binder jetting is prone to defects like porosity, which decreases the adoption of binder-jetted parts. Binder-jetted parts are sometimes infiltrated with a low melting temperature metal to fill pores during sintering; however, the infiltration is impacted by the part geometry and infiltration environment, which can cause infill nonuniformity. Furthermore, using an infiltration metal creates a complicated multiphase microstructure substantially different than common wrought materials and alloys. To bring insight to the binder jet/infiltration process toward part qualification and improved part quality, spatially dependent ultrasonic wave speed and attenuation techniques are being applied to help characterize and map porosity in parts made by binder jet AM. In this paper, measurements are conducted on binder-jetted stainless steel and stainless steel infiltrated with bronze samples. X-ray computed tomography (XCT) is used to provide an assessment of porosity.

Direct writing of self-healing circuits on curvilinear surfaces

Directly written circuits on polymeric housings can reduce weight and enhance flexibility due to the wiring of electronic devices and systems in automotive and aerospace parts. These circuits must conform to a variety of geometries while maintaining electrical conductivity after deformations. To address these challenges, a hybrid copper-based ink has been developed capable of self-healing. Low melting temperature metals such as indium can work as a self-healing agent in response to deformational processes such as thermoforming. A new generation of devices is conceptualized utilizing printable hybrid copper-based ink, sintered and healed within a few milliseconds via intense pulsed light (IPL).

Chemical kinetics modelling for the effect of chimney on diffusion flame in carbon nanotubes synthesis

Hydrocarbon flame syntheses of carbon nanotubes (CNTs) on various metals substrates have been reported in literature, but existing methods are limited to usage of high melting temperature metals substrate due to excessive temperature in conventional diffusion flame burner. To address this limitation, high thermal conductivity chimney is innovatively incorporated into the diffusion burner to control flame temperature. Hence, the aim of this study is to investigate the effect of chimney application on the interaction behaviour between flame temperature profile and concentration of post combustion species distribution of diffusion flame. In this study, Computational Fluids Dynamics (CFD) – Chemical Kinetics (Chemkin) coupling method is used to simulate the flow and transport behaviour of laminar methane-air mixture in combustion environment. Kinetics mechanism is imported into species transport model of Chemkin simulator to further determine the reaction between combustion species and temperature profile of the mixture. Heat transfer models are then integrated into simulation to investigate the cooling effect of chimney during the combustion of methane-air mixture. This numerical simulation study provides insights on effects of chimney application towards cooling, species concentration, flame temperature and paving path for controlling the growth of CNT on low melting temperature metal substrate. Numerical models show improvement in temperature controls, increase in gas species concentration and in surface area that is favourable for growth of CNTs.

Customizing MRI-Compatible Multifunctional Neural Interfaces through Fiber Drawing.

Fiber drawing enables scalable fabrication of multifunctional flexible fibers that integrate electrical, optical and microfluidic modalities to record and modulate neural activity. Constraints on thermomechanical properties of materials, however, have prevented integrated drawing of metal electrodes with low-loss polymer waveguides for concurrent electrical recording and optical neuromodulation. Here we introduce two fabrication approaches: (1) an iterative thermal drawing with a soft, low melting temperature (Tm) metal indium, and (2) a metal convergence drawing with traditionally non-drawable high Tm metal tungsten. Both approaches deliver multifunctional flexible neural interfaces with low-impedance metallic electrodes and low-loss waveguides, capable of recording optically-evoked and spontaneous neural activity in mice over several weeks. We couple these fibers with a light-weight mechanical microdrive (1g) that enables depth-specific interrogation of neural circuits in mice following chronic implantation. Finally, we demonstrate the compatibility of these fibers with magnetic resonance imaging (MRI) and apply them to visualize the delivery of chemical payloads through the integrated channels in real time. Together, these advances expand the domains of application of the fiber-based neural probes in neuroscience and neuroengineering.

Additive Manufacturing by laser-assisted drop deposition from a metal wire

The subject of Additive Manufacturing includes numerous techniques, some of which have reached very high levels of development and are now used industrially. Other techniques such as Micro Droplet Deposition Manufacture are under development and present different manufacturing possibilities, but are employed only for low melting temperature metals. In this paper, the possibility of using a laser-based drop deposition technique for stainless-steel wire is investigated. This technique is expected to be a more flexible alternative to Laser Metal Wire Deposition. Laser Droplet Generation experiments were carried out in an attempt to accurately detach steel drops towards a desired position. High-speed imaging was used to observe drop generation and measure the direction of detachment of the drops. Two drop detachment techniques were investigated and the physical phenomena leading to the drop detachment are explained, wherein the drop weight, the surface tension and the recoil pressure play a major role. Optimised parameters for accurate single drop detachment were identified and then used to build multi-drop tracks. Tracks with an even geometry were produced, where the microstructure was influenced by the numerous drop depositions. The tracks showed a considerably higher hardness than the base wire, exhibiting a relatively homogeneous macro-hardness with a localised softening effect at the interfaces between drops.

Design Principles and Applications of Next-Generation High-Energy-Density Batteries Based on Liquid Metals.

Increasing need for the renewable energy supply accelerated the thriving studies of Li-ion batteries, whereas if the high-energy-density Li as well as alkali metals should be adopted as battery electrodes is still under fierce debate for safety concerns. Recently, a group of low-melting temperature metals and alloys that are in liquid phase at or near room-temperature are being reported for battery applications, by which the battery energy could be improved without significant dendrite issue. Besides the dendrite-free feature, liquid metals can also promise various high-energy-density battery designs on the basis of unique materials properties. In this review, the design principles for liquid metals-based batteries from mechanical, electrochemical, and thermodynamical aspects are provided. With the understanding of the theoretical basis, currently reported relevant designs are summarized and analyzed focusing on the working mechanism, effectiveness evaluation, and novel application. An overview of the state-of-the-art liquid metal battery developments and future prospects is also provided in the end as a reference for further research explorations.

Layup-only modulization for low-stress fabrication of a silicon solar module with 100 μm thin silicon solar cells

Despite the predominance of solar modules with bulk crystalline silicon solar cells as a result of their high photoconversion efficiency, long-lasting durability, and low cost per electrical watt, the competitive market has elevated the necessity of thinner silicon solar cells to further reduce direct material costs. However, the tabbing and stringing process using high melting temperature soldering in the conventional fabrication method of a silicon solar module is required to alternatingly interconnect adjacent silicon solar cells, which entails significant thermomechanical stress. The lifting up-and-down motions in the layup process of serially stringed silicon solar cells also lead to an unfavourable interfacial stress between metal ribbons and silicon solar cells. Consequently, a considerably poor yield of silicon solar modules with the unbearable breakage loss of thin silicon solar cells is ascribed to such processes. Herein, an innovative solution to interconnect thin silicon solar cells through virtually no thermomechanical stress is proposed by using encapsulants pre-attached with low melting temperature metal ribbons at 139 °C, which allow the interconnection of pre-laid silicon solar cells in the course of the vacuum lamination at 160 °C. The resulting silicon solar modules exhibit a photoconversion efficiency of 19.1 ± 0.1%, which represents 99.9 ± 0.6% of the benchmark photoconversion efficiency of conventional silicon solar modules. The presented layup-only modulization succeeds in fabricating silicon solar modules with 100 μm thin silicon solar cells and it is anticipated to curtail the breakage loss of thin silicon solar cells as well as elevate fabrication productivity by simplifying the fabrication steps of silicon solar modules.

Hierarchical nanostructured aluminum alloy with ultrahigh strength and large plasticity

High strength and high ductility are often mutually exclusive properties for structural metallic materials. This is particularly important for aluminum (Al)-based alloys which are widely commercially employed. Here, we introduce a hierarchical nanostructured Al alloy with a structure of Al nanograins surrounded by nano-sized metallic glass (MG) shells. It achieves an ultrahigh yield strength of 1.2 GPa in tension (1.7 GPa in compression) along with 15% plasticity in tension (over 70% in compression). The nano-sized MG phase facilitates such ultrahigh strength by impeding dislocation gliding from one nanograin to another, while continuous generation-movement-annihilation of dislocations in the Al nanograins and the flow behavior of the nano-sized MG phase result in increased plasticity. This plastic deformation mechanism is also an efficient way to decrease grain size to sub-10 nm size for low melting temperature metals like Al, making this structural design one solution to the strength-plasticity trade-off.

Towards digital metal additive manufacturing via high-temperature drop-on-demand jetting

Drop-on-demand jetting of metals offers a fully digital manufacturing approach to surpass the limitations of the current generation powder-based additive manufacturing technologies. However, research on this topic has been restricted mainly to near-net shaping of relatively low melting temperature metals. Here it is proposed a novel approach to jet molten metals at high-temperatures (>1000 °C) to enable the direct digital additive fabrication of micro- to macro-scale objects. The technique used in our research – “MetalJet” - is discussed by studying the ejection and the deposition of two example metals, tin and silver. The applicability of this new technology to additive manufacturing is evaluated through the study of the interface formed between the droplets and the substrate, the inter-droplets bonding, the microstructure and the geometrical fidelity of the printed objects. The research shows that the integrity of the samples (in terms of density as well as metallurgy) varies dramatically in the two investigated materials due to the different conditions that are required to melt the interface of the stacked droplets. Nevertheless the research shows that by a careful choice of the jetting strategy and sintering treatments 3D structures of various complexity can be formed. This research paves the way towards the next generation metal additive manufacturing where various printing resolutions and multi-material capabilities could be used to obtain functional components for applications in printed electronics, medicine and the automotive sectors.

Probing Plasticity and Strain-Rate Effects of Indium Submicron Pillars Using Synchrotron Laue X-Ray Microdiffraction

Mechanical behaviors and especially the strain-rate responses at the nanoscales of low melting temperature metals, such as indium, have not been studied much. Indium is one of the key materials or alloy components in advanced microelectronics and the nanotechnology industry, and understanding their mechanical behaviors at nanoscales becomes increasingly important to ensure lifetime reliability of their applications in novel nanoscale devices or advanced systems (for packaging at the nanoscales, for instance). Synchrotron X-ray microdiffraction has been utilized to examine defect structures of nanoscale materials as well as their strain-rate responses. Nanoscale or advanced microelectronics packaging, for instance, require acceptable levels of drop test results. For these low melting temperature materials especially, this technique offers a unique advantage as conventional methods such as transmission electron microscope and EBSD will expose the structure to high-energy electron beams that may significantly alter the microstructure and defect structure during analysis. Using this approach, we found interesting differences in term of X-ray peak broadening after deformation with different strain rates, which could indicate differences in plasticity mechanisms in the submicron pillars of indium, which could be important for their applications in nanodevices. Understanding these differences could lead to better control of mechanical properties of low melting temperature metals at the nanoscales and, thus, have important implications for nanodevice reliability.

Catalytic molten metals for the direct conversion of methane to hydrogen and separable carbon.

Metals that are active catalysts for methane (Ni, Pt, Pd), when dissolved in inactive low-melting temperature metals (In, Ga, Sn, Pb), produce stable molten metal alloy catalysts for pyrolysis of methane into hydrogen and carbon. All solid catalysts previously used for this reaction have been deactivated by carbon deposition. In the molten alloy system, the insoluble carbon floats to the surface where it can be skimmed off. A 27% Ni-73% Bi alloy achieved 95% methane conversion at 1065°C in a 1.1-meter bubble column and produced pure hydrogen without CO2 or other by-products. Calculations show that the active metals in the molten alloys are atomically dispersed and negatively charged. There is a correlation between the amount of charge on the atoms and their catalytic activity.

Sonication‐Assisted Synthesis of Gallium Oxide Suspensions Featuring Trap State Absorption: Test of Photochemistry

AbstractGallium is a near room temperature liquid metal with extraordinary properties that partly originate from the self‐limiting oxide layer formed on its surface. Taking advantage of the surface gallium oxide (Ga2O3), this work introduces a novel technique to synthesize gallium oxide nanoflakes at high yield by harvesting the self‐limiting native surface oxide of gallium. The synthesis process follows a facile two‐step method comprising liquid gallium metal sonication in DI water and subsequent annealing. In order to explore the functionalities of the product, the obtained hexagonal α‐Ga2O3 nanoflakes are used as a photocatalytic material to decompose organic model dyes. Excellent photocatalytic activity is observed under solar light irradiation. To elucidate the origin of these enhanced catalytic properties, the electronic band structure of the synthesized α‐Ga2O3 is carefully assessed. Consequently, this excellent photocatalytic performance is associated with an energy bandgap reduction, due to the presence of trap states, which are located at ≈1.65 eV under the conduction band minimum. This work presents a novel route for synthesizing oxide nanostructures that can be extended to other low melting temperature metals and their alloys, with great prospects for scaling up and high yield synthesis.

High aspect ratio metal microcasting by hot embossing for X-ray optics fabrication

Metal microstructured optical elements for grating-based X-ray phase-contrast interferometry were fabricated by using an innovative approach of microcasting: hot embossing technology with low melting temperature (280°C) metal alloy foils and silicon etched templates. A gold-tin alloy (80wt% Au/20wt% Sn) was used to cast micro-gratings with pitch sizes in the range of 2 to20μm and depth of the structures up to 80μm. The metal filling of the silicon template strongly depends on the wetting properties of the liquid metal on the groove surface. A thin metal wetting layer (20nm of Ir or Au) was deposited before the casting in order to turn the template surface into hydrophilic with respect of the melted metal alloy. Temperature and pressure of the hot embossing process were optimized for a complete filling of the cavities in a low viscosity regime of the liquid metal, and for minimizing the shear force that might damage the silicon structures for small pitch grating. The new method has relevant advantages, such as being a low cost technique, fast and easily scalable to large area fabrication.

Probing Plasticity Mechanisms in Low Melting Temperature Metallic Nanostructures Using Synchrotron X-Ray Microdiffraction

A nondestructive ex situ Synchrotron Laue X-ray Microdiffraction (µSLXRD) technique is used to investigate the plasticity mechanisms in the metallic nanostructures and their evolution at high homologous temperatures through analyzing low melting temperature metals such as tin. Without the use of expensive high temperature equipment, the current approach of studying plasticity mechanisms at high temperature is enabled by the low melting behaviors of the samples allowing them to provide insights on high temperature deformation mechanisms, such as thermally activated dislocation climbs. Nanopillars with a diameter near 1µm were deformed by uniaxial compression to strains of in excess of 20% at a strain rate of approximately 0.001s-1. Defect density evolution in the nanopillars was evaluated by synchrotron Laue X-ray microdiffraction (µSLXRD) before and after deformation (ex situ). It was found from the Laue peak broadening measurements that there was no significant change in the dislocation density of the same pillar before and after such an extent of deformation. These findings were being compared to similar experimental results of indium and gold nanopillars (from our previous reports). They were found to be in stark contrast to our previous results with indium (although both are low melting temperature metals) where the synchrotron Laue X-ray microdiffraction showed significant peak broadening – before vs. after the uniaxial compression to a similar amount of deformation. It appears high temperature plasticity mechanism in tin nanostructures involves significant lattice diffusion behavior, as opposed to simple displactive behavior (through dislocation movements) that has been proposed in recent studies of tin nanostructures.

Synergistically improved thermal conductivity of polyamide-6 with low melting temperature metal and graphite

Synergistically improved thermal conductivity of polyamide-6 with low melting temperature metal and graphite

Substrate temperature control for the formation of metal nanohelices by glancing angle deposition

The targets of this study are to develop a device to precisely control the temperature during glancing angle deposition, to make films consisting of low melting temperature metal nanoelements with a controlled shape (helix), and to explore the substrate temperature for controlling the nanoshapes. A vacuum evaporation system capable of both cooling a substrate and measurement of its temperature was used to form thin films consisting of arrays of Cu and Al nanohelices on silicon substrates by maintaining the substrate temperature at Ts/Tm < 0.22 (Ts is the substrate temperature and Tm is the melting temperature of target material). The critical Ts/Tm to produce Cu and Al nanohelices corresponds to the transitional homologous temperature between zones I and II in the structure zone model for the solid film, where surface diffusion becomes dominant. X-ray diffraction analysis indicated that the Cu and Al nanohelix thin films were composed of coarse oriented grains with diameters of several tens of nanometers.

Printing Three-Dimensional Electrical Traces in Additive Manufactured Parts for Injection of Low Melting Temperature Metals

While techniques exist for the rapid prototyping of mechanical and electrical components separately, this paper describes a method where commercial additive manufacturing (AM) techniques can be used to concurrently construct the mechanical structure and electronic circuits in a robotic or mechatronic system. The technique involves printing hollow channels within 3D printed parts that are then filled with a low melting point liquid metal alloy that solidifies to form electrical traces. This method is compatible with most conventional fused deposition modeling and stereolithography (SLA) machines and requires no modification to an existing printer, though the technique could easily be incorporated into multimaterial machines. Three primary considerations are explored using a commercial fused deposition manufacturing (FDM) process as a testbed: material and manufacturing process parameters, simplified injection fluid mechanics, and automatic part generation using standard printed circuit board (PCB) software tools. Example parts demonstrate the ability to embed circuits into a 3D printed structure and populate the surface with discrete electronic components.

Development of an enhanced liquid for electronic cooling

Development of NEPCM (Nanoparticle Encapsulated Phase Change Material) nanofluids using low melting temperature metals is a very pertinent area of research in the context of effective thermal management solutions. Compared to a pure fluid, these nanofluids have a higher heat capacity during the phase change and it is possible to improve the heat transfer, as a result of this phase change. To appreciate the merits, in terms of energy, an energy Performance Evaluation Criteria (PEC) has been defined as the ratio of heat transfer rate at fixed pumping power. The numerical results obtained show an improvement around 20% of this energetic criterion at low ΔT compared to the base fluid. A status of the development of these fluids in our laboratory is given in this paper. From an experimental point of view, a specific test loop has been developed in order to test thermo hydraulic performance in a controlled manner in laminar and turbulent conditions at imposed heat flux with a small volume of fluid (350 ml). The test loop was validated with pure water and the choice of materials used has been defined but not yet tested.