Multi-Bandgap Monolithic Metal Nanowire Percolation Network Sensor Integration by Reversible Selective Laser-Induced Redox

Active electronics are usually composed of semiconductor and metal electrodes which are connected by multiple vacuum deposition steps and photolithography patterning.However,the presence of interface of dissimilar material between semiconductor and metal electrode makes various problems in electrical contacts and mechanical failure.The ideal electronics should not have defective interfaces of dissimilar materials.In this study,we developed a novel method to fabricate active electronic components in a monolithic seamless fashion where both metal and semiconductor can be prepared from the same monolith material without creating a semiconductor-metal interface by reversible selective laser-induced redox(rSLIR)method.Furthermore,rSLIR can control the oxidation state of transition metal(Cu)to yield semiconductors with two different bandgap states(Cu_(2)O and CuO with bandgaps of 2.1 and 1.2 eV,respectively),which may allow multifunctional sensors with multiple bandgaps from the same materials.This novel method enables the seamless integration of single-phase Cu,Cu_(2)O,and CuO,simultaneously while allowing reversible,selec-tive conversion between oxidation states by simply shining laser light.Moreover,we fabricated a flexible monolithic metal-semiconduc-tor-metal multispectral photodetector that can detect multiple wavelengths.The unique monolithic characteristics of rSLIR process can provide next-generation electronics fabrication method overcoming the limitation of conventional photolithography methods.

Piezoelectric strain sensor with high sensitivity and high stretchability based on kirigami design cutting

Wearable technology requires high-performance sensors with properties such as small size,flexibility,and wireless communication.Stretchability,sensitivity,and tunability are crucial sensor properties;stretchability and sensitivity ensure user comfort and accurate sensing performance,while tunability is essential for implementing sensors in diverse applications with different ranges of motion.In this study,we developed a high performance kirigami piezoelectric strain sensor.Using finite element analysis,the sensing performance was evaluated,and the kirigami patterns were optimized.The electromechanical properties of sensors with four different kirigami patterns were analyzed.A sensor voltage measurement circuit was also designed,amplifying the output voltage 86.5 times by improving measurement accuracy.A piezoelectric kirigami sensor was constructed with a sensitivity of 9.86 V/cm^(2) and a stretchability of 320.8%,higher than those of previously reported kirigami piezoelectric strain sensors.Finally,the fabricated sensor was successfully applied in a haptic glove for playing musical instruments.

Single-input single-output multi-touch soft sensor systems using band-pass filters

In many soft sensor systems,external wires for connecting the sensors to control circuits have posed practical problems,in terms of compact form factors and physical robustness.This study proposes a design of soft sensor arrays that can operate with a drastically reduced number of wires without degrading the original performance.The proposed concept is an array of soft sensing modules,each of which consists of an inductor and a capacitor embedded next to the resistive sensing module,constructing a resistorinductor-capacitor band-pass filter.By adjusting the values of the capacitance and the inductance,unique frequency band is assigned to each sensing module,enabling the distinctive detection using only two external wires regardless of the number of modules.The multi-touch sensing functionality of the system is analytically modeled and experimentally characterized.Taking advantage of the design,a fingertip tactile sensor and an insole foot pressure sensor are demonstrated as practical applications.

Liquid-metal micro-networks with strain-induced conductivity for soft electronics and robotic skin

Thin-film devices made of room-temperature liquid metals(LMs)have contributed to the development of electronic skin for human-robot/machine interfaces but still have limitations,including degradations of performance and robustness under repeated deformations.In this paper,we describe an interesting phenomenon of the formation of LM microscale networks(LMMNs)and propose to use the LMMNs for fabricating thin-film conductors.A simple layer-by-layer(LBL)deposition process enables the growth of a hierarchical structure of LM microdroplets that forms a conductive network(i.e.,LMMN)when stretched.The strain-history behavior of LMMNs allows conductivity enhancement up to 2.37×10^(6) S m^(-1) in response to increased tensile strains.By adjusting the number of LM layers in LBL deposition,the gauge factor(0.2≤GF≤1),the linearity,and the sheet resistance of LMMN films can be easily controlled,providing high potentials in various applications,including skin-mountable circuits,energy harvesters,and soft artificial skin.

Nanowire-assisted freestanding liquid metal thin-film patterns for highly stretchable electrodes on 3D surfaces

Stretchable electronics is playing an integral role in fields such as wearable electronics and soft robots.Among soft conductive materials,liquid metal is drawing intense attention as an electrode material due to its liquid nature at room temperature.However,the merits of liquid metal conductor are limited by the presence of substrates or enclosed microchannels from physical disturbances by the underlying substrate when applying it to 3D surface and modifying complex circuit.To overcome this limitation,we develop freestanding patterned liquid metal thin-film conductor(FS-GaIn).FS-GaIn was achieved by introducing metal nanowires to liquid metal and subsequent sequential selective laser processing and etching of directly patterned traces.FSGaIn can be applied directly to nonflat surface without substrates.When incorporated into electrical circuits,FS-GaIn shows high electrical conductivity,stretchability,and stability.The concept of freestanding liquid metal can open a functionality to the conventional liquid metal electronics.

Experimental Investigation of Aerodynamic Performance due to Blade Tip Clearance in a Gas Turbine Rotor Cascade

This study examines how the complex flow structure within a gas turbine rotor affects aerodynamic loss. An unshrouded linear turbine cascade was built, and velocity and pressure fields were measured using a 5-hole probe. In order to elucidate the effect of tip clearance, the overall aerodynamic loss was evaluated by varying the tip clearance and examining the total pressure field for each case. The tip clearance was varied from 0% to 4.2% of blade span and the chord length based Reynolds number was fixed at 2×10^(5). For the case without tip clearance, a wake downstream of the blade trailing edge is observed, along with hub and tip passage vortices. These flow structures result in profile loss at the center of the blade span, and passage vortex related losses towards the hub and tip. As the tip clearance increases, a tip leakage vortex is formed, and it becomes stronger and eventually alters the tip passage vortex. Because of the interference of the secondary tip leakage flow with the main flow, the streamwise velocity decreases while the total pressure loss increases significantly by tenfold in the last 30% blade span region towards the tip for the 4.2% tip clearance case. It was additionally observed that the overall aerodynamic loss increases linearly with tip clearance.

U-IMPACT:a universal 3D microfluidic cell culture platform

The development of organs-on-a-chip has resulted in advances in the reconstruction of 3D cellular microenvironments.However,there remain limitations regarding applicability and manufacturability.Here,we present an injection-molded plastic array 3D universal culture platform(U-IMPACT)for various biological applications in a single platform,such as cocultures of various cell types,and spheroids(e.g.,tumor spheroids,neurospheres)and tissues(e.g.,microvessels).The U-IMPACT consists of three channels and a spheroid zone with a 96-well plate form factor.Specifically,organoids or spheroids(~500μm)can be located in designated areas,while cell suspensions or cellladen hydrogels can be selectively placed in three channels.For stable multichannel patterning,we developed a new patterning method based on capillary action,utilizing capillary channels and the native contact angle of the materials without any modification.We derived the optimal material hydrophilicity(contact angle of the body,45–90°;substrate,<30°)for robust patterning through experiments and theoretical calculations.We demonstrated that the U-IMPACT can implement 3D tumor microenvironments for angiogenesis,vascularization,and tumor cell migration.Furthermore,we cultured neurospheres from induced neural stem cells.The U-IMPACT can serve as a multifunctional organ-on-achip platform for high-content and high-throughput screening.

CAD/CAM for scalable nanomanufacturing:A network-based system for hybrid 3D printing

Micro-and nano-structuring have been highlighted over several decades in both science and engineering fields.In addition to continuous efforts in fabrication techniques,investigations in scalable nanomanufacturing have been pursued to achieve reduced feature size,fewer constraints in terms of materials and dimensional complexity,as well as improved process throughput.In this study,based on recent micro-/nanoscale fabrication processes,characteristics and key requirements for computer-aided design and manufacturing(CAD/CAM)systems for scalable nanomanufacturing were investigated.Requirements include a process knowledge database,standardized processing,active communication,adaptive interpolation,a consistent coordinate system,and management of peripheral devices.For scalable nanomanufacturing,it is important to consider the flexibility and expandability of each process,because hybrid and bridging processes represent effective ways to expand process capabilities.As an example,we describe a novel CAD/CAM system for hybrid three-dimensional(3D)printing at the nanoscale.This novel hybrid process was developed by bridging aerodynamically focused nanoparticle printing,focused ion beam milling,micromachining,and spincoating processes.The system developed can print a full 3D structure using various inorganic materials,with a minimum process scale of 50 nm.The most obvious difference versus CAD/CAM at‘conventional’scales is that our system was developed based on a network to promote communication between users and process operators.With the network-based system,it is also possible to narrow the gap among different processes/resources.We anticipate that this approach can contribute to the development of CAD/CAM for scalable nanomanufacturing and a wide range of hybrid processes.