Direct Writing Micropatterns with a Resolution up to 1 µm

Solution processes have been widely used to fabricate micropatterned surfaces for its mild operation conditions. However, current approaches suffer from limitations of either low resolution or high cost. Here, a facile approach is proposed for direct writing micropatterns with a resolution up to ≈ 1 µm using a unit of triple conical fibers with the side‐by‐side parallel arrangement. With this unit, the resolution of the micropatterns can be mainly controlled by the single central conical fiber, with one side of the fiber facilitating continuous and steady liquid transfer onto the substrate and the other side mechanically supporting the whole unit. Particularly, the unit enables tunable dimension of the micropatterns within a rather large scale from ≈ 1 µm to ≈ 1.3 mm by varying the writing parameters (speed, height, and angle). Moreover, the unit is applicable for direct patterning various liquids, even into microline arrays, with a high resolution. It enables direct writing conductive microline with a width of ≈ 1 µm in a centimeter length scale, which can be used for constructing microcircuits. It is envisioned that the result offers a new perspective for preparing high‐resolution micropatterns using solution processes.     

A Novel Strategy for Preparing Stretchable and Reliable Biphasic Liquid Metal

Low‐melting liquid metal is a hugely promising material for flexible conductive patterns due to its excellent conductivity and supercompliance, especially low‐cost and environmental liquid processing technology. However, the ever‐present fluidity characteristic greatly limits the stable shape and reliability of prepared liquid metal conductive electronics. Herein, a novel solidification strategy of liquid GaIn alloys by Ni doping and heat treatment is first reported, which can efficiently create a solid phase in the liquid metal and provide an effective solution for practical applications. Particularly, the liquid characteristic is preserved for conveniently fabricating different flexible electronic circuits, and then the solidification is carried out on prepared conductive patterns by heat treatment. The solidification mechanism is revealed by the interface chemical reaction between Ni and GaIn, creating the solid phase of intermetallic compound (Ga₄Ni₃ and InNi₃) during heat treatment. Moreover, a biphasic GaInNi can be obtained by regulating the atomic ratio of gallium, indium, and nickel. As a result, the obtained GaInNi possesses extremely low sheet resistance (15 ± 4.5 to 135 ± 2.5 mΩ sq^?1) and the variation of ΔR/R₀ exhibits low level (0–2) when strained up to 100%, which offers a promising strategy to prepare stretchable and reliable liquid metal electronics.     

二元光学器件激光直写技术的研究进展

二元光学器件的激光直写技术可克服传统的半导体工艺(掩模套刻法或多次沉积薄膜法)所带来的加工环节多、对准精度难以控制、周期长、成本高等问题,可进一步提高二元光学器件的制作精度和衍射效率.分析了二元光学器件激光直写的基本原理,对已有的各种激光直写方法和最新研究成果进行了综述,并展望了其发展趋势.     

Liquid Metal Actuator for Inducing Chaotic Advection

Chaotic advection plays an important role in microplatforms for a variety of applications. Currently used mechanisms for inducing chaotic advection in small scale, however, are limited by their complicated fabrication processes and relatively high power consumption. Here, a soft actuator is reported which utilizes a droplet of Galinstan liquid metal to induce harmonic Marangoni flow at the surface of liquid metal when activated by a sinusoidal signal. This liquid metal actuator has no rigid parts and employs continuous electrowetting effect to induce chaotic advection with exceptionally low power consumption. The theory behind the operation of this actuator is developed and validated via a series of experiments. The presented actuator can be readily integrated into other microfluidic components for a wide range of applications.     

Direct Writing of Gallium‐Indium Alloy for Stretchable Electronics

In this paper, a direct writing method for gallium‐indium alloys is presented. The relationships between nozzle inner diameter, standoff distance, flow rate, and the resulting trace geometry are demonstrated. The interaction between the gallium oxide layer and the substrate is critically important in understanding the printing behavior of the liquid metal. The difference between receding and advancing contact angles demonstrates that the adhesion of the oxide layer to the substrate surface is stronger than the wetting of the surface by the gallium‐indium alloy. This further demonstrates why free‐standing structures such as the traces described herein can be realized. In addition to the basic characterization of the direct writing process, a design algorithm that is generalizable to a range of trace geometries is developed. This method is applied to the fabrication of an elastomer‐encapsulated strain gauge that displays an approximately linear behavior through 50% strain with a gauge factor of 1.5.     

Dynamic Photomask‐Assisted Direct Ink Writing Multimaterial for Multilevel Triboelectric Nanogenerator

Triboelectric nanogenerator (TENG) devices are extensively studied as a mechanical energy harvester and self‐powered sensor for wearable electronics and physiological monitoring. However, the conventional TENG fabrication involving assembling steps and using the single property of matrix material suffers from simple devices shape and a single level of mechanical response for sensing and energy harvesting. Here, the printed multimaterial matrix for multilevel mechanical‐responsive TENG with on‐demand reconfiguration of shape is reported. A multimaterial 3D printing approach by using dynamic photomask‐assisted direct ink writing printing together with a two‐stage curing hybrid ink is first developed. Multimaterial structures with location‐specific properties, such as tensile modulus, failure stress, and glass transition temperature for controlled deformation, crack propagation path, and sequential shape memory, are directly printed. The printed multimaterial structure with sequential deformation behavior is used to fabricate a multilevel‐TENG (mTENG) device for multiple level mechanical energy harvesters and sensors. It is demonstrated that the mTENG can be embedded in shoe insoles to achieve both comfortable wearing and motion state monitoring. This work provides a new approach to combine multimaterial 3D printing with TENG devices for functional wearable electronics as energy harvester and sensors.     

A Versatile Approach for Direct Patterning of Liquid Metal Using Magnetic Field

Patterning of liquid metal (LM) is usually an integral step toward its practical applications. However, the high surface tension along with surface oxide makes direct patterning of LM very challenging. Existing LM patterning techniques are designed for limited types of planar substrates, which require multiple‐step operation, delicate molds and masks, and expensive equipment. In this work, a simple, versatile, and equipment‐free approach for direct patterning of LM on various substrates using magnetic field is reported. To achieve this, magnetic microparticles are dispersed into LM by stirring. When a moving magnetic field is applied to the LM droplet, the aggregated magnetic microparticles deform the droplet to a continuous line. In addition, this approach is also applicable to supermetallophobic substrates since the applied magnetic field significantly enhances the contact between LM and substrate. Moreover, remote manipulation of the magnetic microparticles allows direct patterning of LM on nonplanar surfaces, even in a narrow and near closed space, which is impossible for the existing techniques. A few applications are also demonstrated using the proposed technique for flexible electronics and wearable sensors.     

Liquid Metals-Assisted Synthesis of Scalable 2D Nanomaterials: Prospective Sediment Inks for Screen-Printed Energy Storage Applications

The advents in flexible and smart technology like wearable electronics have accelerated the demand for high-performance energy-storage devices. These devices could significantly reduce the size of the next-generation wearable smart electronics. A selection of suitable printing technology and its product typically offer a reasonable manufacturing pathway like high deposition rate, low materials waste, scalable fabrication, and high-performance production. Therefore, the production of novel functional inks with desirable rheological properties that authorize high-resolution printing, are some major challenges of this technology. This work has an emphasis on the recent advancements in supporting and utilizing liquid metals chemistry to synthesis high-quality and scalable 2D nanomaterials by liquid-phase free exfoliation and facile sonication-assisted methods. These are novel concepts in synthesizing 2D nanomaterials particularly for those which either have not intrinsic layered crystal structures or those with strong interaction between their crystal layers which are difficult to synthesized using conventional approaches. It also provides some potentials to make sustainable ink formulation of such 2D nanostructures for the fabrication of high-quality screen-printed patterns for sustainable energy applications. Subsequently, it deals with the possibilities and challenges of printing such 2D nanomaterials (namely, 2D metal oxides) for micro-supercapacitor and micro-battery applications on an industrially viable scale.     

Bio-Inspired Differential Capillary Migration of Aqueous Liquid Metal Ink for Rapid Fabrication of High-Precision Monolayer and Multilayer Circuits

Manipulating liquid metal inks to create conductive microstructures has attracted widespread interest as liquid metal microstructures are turning into influential components in flexible electronics. However, it is challenging to prevent the issues with low precision, low efficiency, and residue caused by sedimentation, free diffusion, and the Marangoni effect. Inspired by the water transport in plants, the wetting-induced assembly method based on the differential capillary effect for liquid metal ink is created to realize the facile and rapid manufacture of liquid metal conductive microstructures. The single-micron accuracy circuits with a minimum of ≈4 µm straight lines are fabricated to a centimeter scale. This method can also be extended to the preparation of multilayer circuits (minimum 5 µm through hole). The resulting entirely flexible stretchable circuits make it possible to construct highly stretchable devices, such as flexible transparent conductors and stretching sensors. Transparent conductors exhibit excellent mechanical (maximum ≈750% tensile rupture limit) and optoelectronic properties (the transmittance reaches ≈87% and the sheet resistance is ≈0.5 Ω/□)|making them suitable for optically-clear electromagnetic shielding. This study offers a fresh and plain approach to solving the assembly problem of liquid metal inks, paving the way for the creation of flexible electronic devices     

灰度掩模并行激光直写系统的总体设计

灰度掩模法是一种新的二元光学器件制做方法。研究了并行激光直写高性能灰度掩模的工作原理，对空间光调制器（SML）、精缩投影物镜和二维气浮平台等关键单元进行了分析，给出了并行激光直写系统的主要技术指标和初步实验结果。     

临界角法激光直写聚焦伺服系统静态特性研究

为同时提高金属网栅屏蔽效率及红外透过率,要求激光直写线条细且均匀.而工件面型误差、光刻胶涂布不均匀性、机械轴系误差等会造成写入焦斑离焦,影响线条线宽及均匀性.需引入聚焦伺服系统来实时探测并补偿离焦,确保写入光束实时聚焦在光刻胶面上.给出了临界角法调焦的原理,搭建了由探焦光路、离焦信号前放、压电陶瓷微位移执行机构组成的聚...     

3D Direct Laser Writing of Highly Absorptive Photoresist for Miniature Optical Apertures

The importance of 3D direct laser writing as an enabling technology increased rapidly in recent years. Complex micro-optics and optical devices with various functionalities are now feasible. Different possibilities to increase the optical performance are demonstrated, for example, multi-lens objectives, a combination of different photoresists, or diffractive optical elements. It is still challenging to create fitting apertures for these micro optics. In this work, a novel and simple way to create 3D-printed opaque structures with a highly absorptive photoresist is introduced, which can be used to fabricate microscopic apertures increasing the contrast of 3D-printed micro optics and enabling new optical designs. Both hybrid printing by combining clear and opaque resists, as well as printing transparent optical elements and their surrounding opaque apertures solely from a single black resist by using different printing thicknesses are demonstrated.     

Liquid Metal Supercooling for Low‐Temperature Thermoelectric Wearables

Elastomers embedded with droplets of liquid metal (LM) alloy represent an emerging class of soft multifunctional composites that have potentially transformative impact in wearable electronics, biocompatible machines, and soft robotics. However, for these applications it is crucial for LM alloys to remain liquid during the entire service temperature range in order to maintain high mechanical compliance throughout the duration of operation. Here, LM‐based functional composites that do not freeze and remain soft and stretchable at extremely low temperatures are introduced. It is shown that the confinement of LM droplets to micro‐/nanometer length scales significantly suppresses their freezing temperature (down to ?84.1 from ?5.9 °C) and melting point (down to ?25.6 from +17.8 °C) independent of the choice of matrix material and processing conditions. Such a supercooling effect allows the LM inclusions to preserve their fluidic nature at low temperatures and stretch with the surrounding polymer matrix without introducing significant mechanical resistance. These results indicate that LM composites with highly stabilized droplets can operate over a wide temperature range and open up new possibilities for these emerging materials, which are demonstrated with self‐powered wearable thermoelectric devices for bio‐sensing and personal health monitoring at low temperatures.     

Ultrasoft Liquid Metal Elastomer Foams with Positive and Negative Piezopermittivity for Tactile Sensing

Soft, capacitive tactile (pressure) sensors are important for applications including human–machine interfaces, soft robots, and electronic skins. Such capacitors consist of two electrodes separated by a soft dielectric. Pressing the capacitor brings the electrodes closer together and thereby increases capacitance. Thus, sensitivity to a given force is maximized by using dielectric materials that are soft and have a high dielectric constant, yet such properties are often in conflict with each other. Here, a liquid metal elastomer foam (LMEF) is introduced that is extremely soft (elastic modulus 7.8 kPa), highly compressible (70% strain), and has a high permittivity. Compressing the LMEF displaces the air in the foam structure, increasing the permittivity over a large range (5.6–11.7). This is called “positive piezopermittivity.” Interestingly, it is discovered that the permittivity of such materials decreases (“negative piezopermittivity”) when compressed to large strain due to the geometric deformation of the liquid metal droplets. This mechanism is theoretically confirmed via electromagnetic theory, and finite element simulation. Using these materials, a soft tactile sensor with high sensitivity, high initial capacitance, and large capacitance change is demonstrated. In addition, a tactile sensor powered wirelessly (from 3 m away) with high power conversion efficiency (84%) is demonstrated.     

A Liquid Metal Based Multimodal Sensor and Haptic Feedback Device for Thermal and Tactile Sensation Generation in Virtual Reality

Virtual reality (VR) has been widely used for training, gaming, and entertainment, and the value of VR is continually increasing as a contact-free technology. For an immersive VR experience, measuring finger movements and providing appropriate feedback to the hand are as important as visual information, given the necessity of the hands for activities in daily life. Thus, a hand-worn VR device with motion sensors and haptic feedback is desirable. In this paper, a multimodal sensing and feedback glove is developed with soft, stretchable, lightweight, and compact sensor and heater sheets manufactured by direct ink writing (DIW) of liquid metal, eutectic gallium-indium (eGaIn). In the sensor sheet, ten sensors and three vibrators are embedded to measure finger movements and provide vibro-haptic feedback. The other heater sheet provides thermo-haptic sensation in accurate and rapid manner via model-based feedback control even under stretched conditions. The multimodal sensing and feedback glove allows users to feel the contact status and discriminate materials with different temperature. Performance of the proposed multimodal glove is verified under VR environments including touching and pushing two blocks of different materials and grabbing a heated metal ball submerged in hot water.     

Direct Laser Writing of Superhydrophobic PDMS Elastomers for Controllable Manipulation via Marangoni Effect

Direct light‐to‐work conversion enables manipulating remote devices in a contactless, controllable, and continuous manner. Although some pioneering works have already proven the feasibility of controlling devices through light‐irradiation‐induced surface tension gradients, challenges remain, including the flexible integration of efficient photothermal materials, multifunctional structure design, and fluidic drag reduction. This paper reports a facile one‐step method for preparing light‐driven floating devices with functional surfaces for both light absorption and drag reduction. The direct laser writing technique is employed for both arbitrary patterning and surface modification. By integrating the functional layer at the desired position or by designing asymmetric structures, three typical light‐driven floating devices with fast linear or rotational motions are demonstrated. Furthermore, these devices can be driven by a variety of light sources including sunlight, a filament lamp, or laser beams. The approach provides a simple, green, and cost‐effective strategy for building functional floating devices and smart light‐driven actuators.     

液氩冷却对316L激光金属直接成形零件组织和显微硬度的影响

在激光金属直接成形过程中,为了使熔池在凝固时始终保持合理的温度梯度从而使成形件内部柱状晶组织自基板起从下到上延续生长,在成形316 L实体墙过程中采用液氩喷射冷却的方法降低成形件的温度;分析了液氩喷射冷却对实体墙金相组织和显微硬度的影响。结果显示,采用液氩喷射冷却能有效缓解激光金属直接成形过程中成形件内部的热积累现象,使柱状晶组织在实体墙内部从基板开始从下到上延续生长,一次枝晶间距最大处约为12μm,并且提高了实体墙零件的显微硬度值。     

Liquid Metal Droplets Wrapped with Polysaccharide Microgel as Biocompatible Aqueous Ink for Flexible Conductive Devices

Nanometerization of liquid metal in organic systems can facilitate deposition of liquid metals onto substrates and then recover its conductivity through sintering. Although having broader potential applications, producing stable aqueous inks of liquid metals keeps challenging because of rapid oxidation of liquid metal when exposing to water and oxygen. Here, a biocompatible aqueous ink is produced by encapsulating alloy nanodroplets of gallium and indium (EGaIn) into microgels of marine polysaccharides. During sonicating bulk EGaIn in aqueous alginate solution, alginate not only facilitates the downsizing process via coordination of their carboxyl groups with Ga ions but also forms microgel shells around EGaIn droplets. Due to the deceasing oxygen‐permeability of microgel shells, aqueous ink of EGaIn nanodroplets can maintain colloidal and chemical stability for a period of >7 d. Crosslinked alginate‐gel with tunable thickness can retard the generation and release of toxic cations, thereby affording high biocompatibility. The soft alginate shells also enable to recover electric conductivity of EGaIn layers by “mechanical sintering” for applications in microcircuits, electric‐thermal actuators, and wearable sensors, offering huge potential for electronic tattoos, artificial limbs, electric skins, etc.     

Liquid Metal Based Island‐Bridge Architectures for All Printed Stretchable Electrochemical Devices

The adoption of epidermal electronics into everyday life requires new design and fabrication paradigms, transitioning away from traditional rigid, bulky electronics towards soft devices that adapt with high intimacy to the human body. Here, a new strategy is reported for fabricating achieving highly stretchable “island‐bridge” (IB) electrochemical devices based on thick‐film printing process involving merging the deterministic IB architecture with stress‐enduring composite silver (Ag) inks based on eutectic gallium‐indium particles (EGaInPs) as dynamic electrical anchors within the inside the percolated network. The fabrication of free‐standing soft Ag‐EGaInPs‐based serpentine “bridges” enables the printed microstructures to maintain mechanical and electrical properties under an extreme (≈800%) strain. Coupling these highly stretchable “bridges” with rigid multifunctional “island” electrodes allows the realization of electrochemical devices that can sustain high mechanical deformation while displaying an extremely attractive and stable electrochemical performance. The advantages and practical utility of the new printed Ag‐liquid metal‐based island‐bridge designs are discussed and illustrated using a wearable biofuel cell. Such new scalable and tunable fabrication strategy will allow to incorporate a wide range of materials into a single device towards a wide range of applications in wearable electronics.     

Facile and Rapid Method for Fabricating Liquid Metal Electrodes with Highly Precise Patterns via One‐Step Coating

Gallium‐based alloys, which are virtually non‐toxic liquid metals at room temperature, are considered highly promising electrode materials for state‐of‐the‐art electronics with new form factors. Herein, a facile and rapid method to fabricate liquid metal electrodes with highly precise patterns via a one‐step coating is presented. For this work, polymeric stencil masks with dual structures, comprising upper and lower structures for injecting and molding the liquid metal, respectively, are used for direct patterning of the liquid metal via spray deposition for few seconds, enabling the formation of complex and minute patterns including long thin lines and hollow forms. This method can be adapted to 3D substrates of various materials without any surface treatment, owing to the intrinsic adhesive and flexible properties of the polymeric masks ensuring conformal contact with non‐flat surfaces, and is also expected to be applicable to sub‐micron patterns. In addition, a number of highly flexible/stretchable electronic applications, exhibiting no change in electrical conductivity upon consecutive structural deformations, are demonstrated on various substrates including human skin. It is anticipated that these results will not only spur the further development of flexible/stretchable electronics, but also significantly contribute to the innovative on‐site fabrication of wearable electronics with high durability.