Universal cryogenic transfer of liquid metal particles in polymers for wafer-scale stretchable integrated electronics.

Liquid metal (LM) offers exceptional potential for stretchable and flexible applications due to its outstanding stretchability, flexibility, and electrical conductivity. The inherent characteristics of LM–such as high surface tension, low viscosity, poor wettability, and sintering challenges–pose significant obstacles for use in commercial printing. To overcome these, a self‐sintering liquid metal composite particle (LMCP) ink with tunable surface tension, viscosity, and wettability is developed. LMCP inks are tailored for commercial printing processes requiring low surface tension and high viscosity, enabling printing on diverse substrates. The ink achieves coffee‐ring‐free, crack‐free, bilayer‐free, and post‐processing‐free deposition through simple evaporation under ambient conditions, while preserving electrical conductivity. Key innovations include: i) utilizing polyvinylpyrrolidone (PVP)‐capped liquid metal particles (LMPs) to reduce surface tension and enhance wettability; ii) incorporating Laponite as a viscosity enhancer and leveraging LMP sedimentation to control viscosity; iii) forming LMCPs encapsulated by PVP and Laponite through co‐self‐assembly on LMP surfaces to promote self‐sintering; and iv) achieving uniform deposition via solutal‐Marangoni‐driven mixing and particle settling. The resulting LMCP electrodes exhibit over 1200% stretchability, patternability into complex configurations, and stability for nearly one year in air. Additionally, their application as stretchable metamaterial absorbers is highlighted, showcasing their potential in advanced printable electronics.

Gallium-based liquid metals (GLMs) are promising anode materials for lithium-ion batteries due to their low-melting point, fluidity, high-electrical and -thermal conductivity, and high-theoretical capacity for Li (769 mAh/g, Li2Ga). Notably, GLMs undergo a reversible liquid-to-solid-to-liquid transition during lithiation and delithiation, enabling a self-healing mechanism that mitigates surface defects. This mechanism extends the cycle life of anodes utilizing GLMs either as active materials( 1–6 ) or in combination with high-volume expansion materials such as silicon (~400%)( 7–9 ).Fundamental studies on the self-healing mechanism of GLMs are limited. Previous investigations have primarily relied on macroscopic characterizations such as X-ray diffraction (XRD) in bulk electrodes( 3,10 ) or in situ transmission electron microscopy (TEM) on individual GLM nanoparticles (NPs) in solid-state cells open to the environment( 6,11 ). In this work, we adopt a multi-scale approach to gain insights into the (de)lithiation mechanism. We conducted: (1) in situ TEM observations of GLM NPs on a TEM grid current collector to simultaneously track lithiation/delithiation dynamics across multiple nanoparticles; (2) cryogenic TEM where GLM NPs on a TEM grid are cycled in a lithium-ion battery electrolyte, and the grid is subsequently transferred to a cryo-TEM for high-resolution interfacial characterization of the GLM NPs; and (3) cryogenic focused-ion beam tomography to analyze structural changes in a composite electrode comprised of GLM NPs, Super P carbon, and PVDF binder on a Cu current collector over continuous cycles within a coin or pouch cell. By investigating GLMs at multiple length scales, this study advances the understanding of how the lithiation/delithiation mechanism of GLM NPs influences capacity fade in lithium-ion batteries. In a broader context, this study establishes a framework for future multi-length scale investigations into battery materials.References Jin, X. et al. Transferring Liquid Metal to form a Hybrid Solid Electrolyte via a Wettability-Tuning Technology for Lithium-Metal Anodes. Adv. Mater. 34, 2200181 (2022).Zhu, M., Li, S., Li, B. & Yang, S. A liquid metal-based self-adaptive sulfur–gallium composite for long-cycling lithium–sulfur batteries. Nanoscale 11, 412–417 (2019).Guo, X. et al. A Self-Healing Room-Temperature Liquid-Metal Anode for Alkali-Ion Batteries. Adv. Funct. Mater. 28, 1804649 (2018).Pu, J. et al. Liquid Metal-Based Stable and Stretchable Zn-Ion Battery for Electronic Textiles. Adv. Mater. 36, 2305812 (2024).Liu, G. et al. Soft, Highly Elastic, and Discharge-Current-Controllable Eutectic Gallium–Indium Liquid Metal–Air Battery Operated at Room Temperature. Adv. Energy Mater. 8, 1703652 (2018).Huang, C. et al. Alkali-ion Batteries by Carbon Encapsulation of Liquid Metal Anode. Adv. Mater. n/a, 2309732.Hapuarachchi, S. N. S. et al. Utilizing Room Temperature Liquid Metals for Mechanically Robust Silicon Anodes in Lithium-Ion Batteries. Batter. Supercaps 1, 122–128 (2018).Ju, Z. et al. Assembled MXene–Liquid Metal Cages on Silicon Microparticles as Self-Healing Battery Anodes. Nano Lett. 24, 6610–6616 (2024).Zhao, Z. et al. Liquid Metal Remedies Silicon Microparticulates Toward Highly Stable and Superior Volumetric Lithium Storage. Adv. Energy Mater. 12, 2103565 (2022).Wang, K. et al. Core-shell GaSn@rGO nanoparticles as high-performance cathodes for room-temperature liquid metal batteries. Scr. Mater. 217, 114792 (2022).Liang, W. et al. Nanovoid Formation and Annihilation in Gallium Nanodroplets under Lithiation–Delithiation Cycling. Nano Lett. 13, 5212–5217 (2013).

Interfacing of surfaces with gallium-based liquid metals – approaches for mitigation and augmentation of liquid metal adhesion on surfaces

This work discusses the attributes, fabrication methods, and applications of gallium‐based liquid metal particles. Gallium‐based liquid metals combine metallic and fluidic properties at room temperature. Unlike mercury, which is toxic and has a finite vapor pressure, gallium possesses low toxicity and effectively zero vapor pressure at room temperature, which makes it amenable to many applications. A variety of fabrication methods produce liquid metal particles with variable sizes, ranging from nm to mm (which is the upper limit set by the capillary length). The liquid nature of gallium enables fabrication methods—such as microfluidics and sonication—that are not possible with solid materials. Gallium‐based liquid metal particles possess several notable attributes, including a metal–metal oxide (liquid–solid) core–shell structure as well as the ability to self‐heal, merge, and change shape. They also have unusual phase behavior that depends on the size of the particles. The particles have no known commercial applications, but they show promise for drug delivery, soft electronics, microfluidics, catalysis, batteries, energy harvesting, and composites. Existing challenges and future opportunities are discussed herein.

Gallium-based liquid metals (GLMs) exist as atypical liquid-phase metals at and near room temperature while being electrically and thermally conductive, enabling copious applications in soft electronics and thermal management systems. Yet, solid metals are affected by interfacing with GLMs, resulting in liquid metal embrittlement and device failure. To avert this issue, mechanically durable and electrically tunable diffusion barriers for long-term reliable liquid metal-solid metal interfacing based on the deposition of various diamond coatings are designed and synthesized, as they feature high chemical inertness and extraordinary mechanical resistance. The diamond coatings show superlyophobicity (GLM contact angle ≥ 155°) and are nonstick toward GLMs, thereby achieving high mobility of GLM droplets (sliding angle 8-12°). The excellent barrier and anti-adhesion performance of the diamond coatings are proven in long-term experiments (3 weeks) of coated titanium alloy (Ti) samples in contact with GLMs. The electrical performance of the conductive diamond coating deposited on Ti is reliable and stable over a period of 50 h. As proof-of-concept applications a switch and a thermal management device based on liquid metals are demonstrated, signifying that coating diamond films on metals is a potent means to achieve stable integration of solid metals with GLMs.

Gallium-based liquid metal (LM) is regarded as one of the most promising candidates for the new-generation jigsaw of stretchable electronics. Nonetheless, the obstacle for the LM application lies in its high surface tension and easy fluidity which leads to great difficulty in handling and processing. Herein, a cross-mechanochemistry between liquid metal and inorganic solid, mediated via the coordination binding between the empty electronic orbits of the former and the lone electron pair of the latter is reported. The mechanism is validated via density functional theory calculation and electron energy loss spectroscopy, and experimentally proven to be universally applicable for various liquid metals and inorganic solids. With the unique mechanochemistry, simple ball milling allows on-demand transformation of the liquid metal into a low-surface-tension liquid, semi-solid paste, or even solid powder. The overcoming of the intrinsic high surface tension of the liquid metal with this approach unleashes the freedom to easily process the liquid metal composites into polymer composites or as direct molding processable paste and printable electronic ink.

Electronic Blood Vessel

Achieving control over the motion of dissolved particles in liquid metals is of importance for the meticulous realization of hierarchical particle assemblies in a variety of nanofabrication processes. Brownian forces can impede the motion of such particles, impacting the degree of perfection that can be realized in assembled structures. Here, we show that light-induced Marangoni flow in liquid metals (i.e., liquid-gallium) with Laguerre-Gaussian (LGpl) lasers as heating sources is an effective approach to overcome Brownian forces on particles, giving rise to predictable assemblies with a high degree of order. We show that by carefully engineering surface tension gradients in liquid-gallium using non-Gaussian LGpl lasers, the Marangoni and convective flow that develops in the fluid drives the trajectory of randomly dispersed particles to assemble into 100 μm wide ring-shaped particle assemblies. Careful control over the parameters of the LGpl laser (i.e., laser mode, spot size, and intensity of the electric field) can tune the temperature and fluid dynamics of the liquid-gallium as well as the balance of forces on the particle. This in turn can tune the structure of the ring-shaped particle assembly with a high degree of fidelity. The use of light to control the motion of particles in liquid metals represents a tunable and rapidly reconfigurable approach to spatially design surface tension gradients in fluids for more complex assembly of particles and small-scale solutes. This work can be extended to a variety of liquid metals, complementary to what has been realized in particle assembly out of ferrofluids using magnetic fields.

Gallium-based liquid metals (LMs) are considered promising electrodes for supercapacitors owing to their metallic conductivity and high deformability. LMs can form nanoparticles via ultrasonication and can be further transformed into rod morphologies via hydrothermal treatment. Remarkably, LM rods exhibit a larger surface area than particles, allowing them to be highly decorated with different metals via galvanic replacement. In this study, a novel electrode is introduced, shape-transformed liquid metal rods decorated with NiCo2O4 nanoneedles anchored on activated carbon. Electrodes with hierarchical structures enhanced the pseudocapacitive performance in an alkaline electrolyte (1.0m KOH), achieving a high specific capacitance of 749.6 F g-1 at 1 A g-1. Owing to the deformability of the LM electrodes as well as the use of LM current collectors, the devices are endowed to be fully soft and exhibited mechanical and electrochemical stability even after cycles of deformation. When assembled into an asymmetric soft supercapacitor with activated carbon as a cathode, the device delivered a specific capacitance of 45 F g-1 at 2 A g-1 and retained 96% of its initial capacitance even after 10 000 galvanostatic charge-discharge (GCD) cycles and after 1 000 mechanical bending cycles with 50% compression, and stretching cycles with 30% elongation.

We report the fabrication and characterization of a reversible resonant frequency tunable antenna based on liquid metal actuation. The antenna is composed of a coplanar waveguide fed monopole stub printed on a copper-clad substrate, and a tunnel-shaped microfluidic channel linked to the printed metal. The gallium-based liquid metal can be injected and withdrawn from the channel in response to an applied air pressure. The gallium-based liquid metal is treated with hydrochloric acid to eliminate the oxide layer, and associated wetting/sticking problems, that arise from exposure to an ambient air environment. Elimination of the oxide layer allows for reliable actuation and repeatable and reversible tuning. By controlling the liquid metal slug on-demand with air pressure, the liquid metal can be readily controllable to connect/disconnect to the monopole antenna so that the physical length of the antenna reversibly tunes. The corresponding reversible resonant frequency changes from 4.9 GHz to 1.1 GHz. The antenna properties based on the liquid metal actuation were characterized by measuring the reflection coefficient and agreed well with simulation results. Additionally, the corresponding time-lapse images of controlling liquid metal in the channel were studied.

Gallium-based liquid metals (LMs) are widely used for stretchable and reconfigurable electronics thanks to their fluidic nature and excellent conductivity. These LMs possess attractive optical properties for photonics applications as well. However, due to the high surface tension of the LMs, it is challenging to form LM nanostructures with arbitrary shapes using conventional nanofabrication techniques. As a result, LM-based nanophotonics has not been extensively explored. Here, a simple yet effective technique is demonstrated to deterministically fabricate LM nanopatterns with high yield over a large area. This technique demonstrates for the first time the capability to fabricate LM nanophotonic structures of various precisely defined shapes and sizes using two different LMs, that is, liquid gallium and liquid eutectic gallium-indium alloy. High-density arrays of LM nanopatterns with critical feature sizes down to ≈100nm and inter-pattern spacings down to ≈100nm are achieved, corresponding to the highest resolution of any LM fabrication technique developed to date. Additionally, the LM nanopatterns demonstrate excellent long-term stability under ambient conditions. This work paves the way toward further development of a wide range of LM nanophotonics technologies and applications.

Gallium-based liquid metals (LMs) featuring both high conductivity and fluidity are ideal conductors for soft and stretchable electronics. However, their liquid nature is a double-edged sword in many key applications since LMs are inherently prone to mechanical damage. Although additional encapsulation is frequently used for the protection of delicate LM electrodes, it hinders the electrical interfacing with other objects for interconnection, sensing, and stimulation. Here, different from conventional patterning methods that deposit LM on or inside substrates, we for the first time report a simple strategy to create surface-embedded LM of eutectic gallium-indium (EGaIn) circuits with mechanical damage endurance. This was achieved by using direct magnetic printing to overcome the high surface tension of LM, allowing it to be passively filled into the laser-patterned microgrooves on soft substrates. We show that the surface-embedded LM circuits are resistant to mechanical erasure, washing, and peeling. We also show the applications of our surface-embedded LM electrodes in respiration monitoring and electrical stimulation of nerves. This work provides a simple and efficient way to create mechanically reliable LM microelectrodes, holding great promise for wearable and implantable bioelectronics.

Conventional rigid electronics are usually unconformable with soft skins and tend to fail in accurate physiological monitoring and precise treatment. Electronic skins (e-Skins) made by conductive and stretchable materials offer mechanical compliance for fabricating flexible and conformable wearables. Compared to common organic or inorganic conductive materials, gallium-based liquid metals alone own superior conductivity and compliance. Here, we demonstrate a highly conductive and stretchable electronic skin with liquid metal circuits (LMCs) embedded in silicone rubber film, which are functionalized for physiological signals monitoring. Through the designs of serpentine structure, LMCs maintained good electrical conductivity and functionality under over 100% strain. Also, a wearable electrocardiogram (ECG) recording device was fabricated and tested. The device was able to acquire steady signals during real-time measurement of physical activities. The proposed liquid metal e-Skin can be further extended to conformable bio-integrated healthcare devices and intelligent health monitoring networks.

Dry liquid metals stabilized by silica particles: Synthesis and application in photothermoelectric power generation

Gallium-based liquid metals (LMs) are materials that possess some unique properties. Just like any other metal, they have high thermal conductivity and low interfacial resistance, but they are in a liquid phase at room temperature. In contrast to mercury alloys, gallium alloys are non-toxic. They don’t evaporate and they can’t be inhaled. The viscosity of those alloys is very similar to water, but they are six times as dense as water. All those properties make Gallium-based liquid metals very good candidates for thermal interface material (TIM) in electronics applications. On the other hand, the reaction and incompatibility of those alloys with some metals is one of the challenges for this type of TIM. The other challenge is that those materials are not just thermally, but also electrically conductive and that is not a desirable property for TIM. A suitable barrier that will prevent any leakage of LMs and the best way to apply the appropriate volume of LM in high-volume production (HVP) would be one of the most important things for any application. A key challenge is applying the liquid metal consistently through a traditional dispensing method due to its property and behavior which involves high surface tension. Through advanced dispensing techniques like jetting technology liquid metal can be applied reliably on a flat, uneven surface or in arrays of minuscule confined spaces or cavities. This paper highlights the dispensing quality, weight repeatability from one substrate to another, and valve hardware stability. This paper will also address the challenges faced during dispensing of liquid metal in high volume manufacturing, and how to achieve desired bondline thickness with jet dispensing for higher throughput and process reliability.