Gold‐Catalyzed Vapor–Liquid–Solid Germanium‐Nanowire Nucleation on Porous Silicon

Nanoporous Si(111) substrates are used to study the effects of Au catalyst coarsening on the nucleation of vapor–liquid–solid‐synthesized epitaxial Ge nanowires (NWs) at temperatures less than 400 °C. Porous Si substrates, with greater effective interparticle separations for Au surface diffusion than nonporous Si, inhibit catalyst coarsening and agglomeration prior to NW nucleation. This greatly reduces the variation in wire diameter and length and increases the yield compared to nucleation on identically prepared nonporous Si substrates.     

Mechanical Terahertz Modulation by Skin‐Like Ultrathin Stretchable Metasurface

The modulation of terahertz plays a key role in realizing the tunable terahertz devices. The concept of flexible and stretchable electronics provides the possibility to dynamically modulate the terahertz with mechanical strain rather than additional electrical components. Here, the mechanical modulation of the terahertz transmission with a freestanding, skin‐like, and highly stretchable metasurface is experimentally illustrated. The stretchable metasurface is fabricated by merely constructing an Al/PI mesh film consisting of serpentine‐like unit cells, with total thickness of only 7 µm. With the flexibility realized by the extremely small thickness, the metasurface can be stretched, bended, and twisted, which provides the possibility to modulate terahertz transmission properties by the mechanical deformation of the metasurface. The terahertz time domain spectroscopy results indicate that the stretchable metasurface shows the band‐stop frequency selective effect and the transmission of the terahertz wave can be modulated from 0.15 to 0.5 with applied external tensile strains up to 28%, while only 3.4% of the shift of the resonance frequency is observed. The mechanisms of the metasurface and the relation between the modulation effect and the structural mesh parameters are also discussed with the electromagnetic simulations and the LC equivalent circuit model.     

A Transparent Nanowire‐Based Cell Impalement Device Suitable for Detailed Cell–Nanowire Interaction Studies

A method to fabricate inexpensive and transparent nanowire impalement devices is invented based on CuO nanowire arrays grown by thermal oxidation. By employing a novel process the nanowires are transferred to a transparent, cell‐compatible epoxy membrane. Cargo delivery and detailed cell‐nanowire interaction studies are performed, revealing that the cell plasma membrane tightly wraps the nanowires, while cell membrane penetration is not observed. The presented device offers an efficient investigation platform for further optimization, leading towards a simple and versatile impalement delivery system.     

Nanowire‐Based Sensors

Nanowires are important potential candidates for the realization of the next generation of sensors. They offer many advantages such as high surface‐to‐volume ratios, Debye lengths comparable to the target molecule, minimum power consumption, and they can be relatively easily incorporated into microelectronic devices. Accordingly, there has been an intensified search for novel nanowire materials and corresponding platforms for realizing single‐molecule detection with superior sensing performance. In this work, progress made towards the use of nanowires for achieving better sensing performance is critically reviewed. In particular, various nanowires types (metallic, semiconducting, and insulating) and their employment either as a sensor material or as a template material are discussed. Major obstacles and future steps towards the ultimate nanosensors based on nanowires are addressed.     

Nanomaterial‐Enabled Stretchable Conductors: Strategies,Materials and Devices

Stretchable electronics are attracting intensive attention due to their promising applications in many areas where electronic devices undergo large deformation and/or form intimate contact with curvilinear surfaces. On the other hand, a plethora of nanomaterials with outstanding properties have emerged over the past decades. The understanding of nanoscale phenomena, materials, and devices has progressed to a point where substantial strides in nanomaterial‐enabled applications become realistic. This review summarizes recent advances in one such application, nanomaterial‐enabled stretchable conductors (one of the most important components for stretchable electronics) and related stretchable devices (e.g., capacitive sensors, supercapacitors and electroactive polymer actuators), over the past five years. Focusing on bottom‐up synthesized carbon nanomaterials (e.g., carbon nanotubes and graphene) and metal nanomaterials (e.g., metal nanowires and nanoparticles), this review provides fundamental insights into the strategies for developing nanomaterial‐enabled highly conductive and stretchable conductors. Finally, some of the challenges and important directions in the area of nanomaterial‐enabled stretchable conductors and devices are discussed.     

High‐Density Stretchable Electrode Grids for Chronic Neural Recording

Electrical interfacing with neural tissue is key to advancing diagnosis and therapies for neurological disorders, as well as providing detailed information about neural signals. A challenge for creating long‐term stable interfaces between electronics and neural tissue is the huge mechanical mismatch between the systems. So far, materials and fabrication processes have restricted the development of soft electrode grids able to combine high performance, long‐term stability, and high electrode density, aspects all essential for neural interfacing. Here, this challenge is addressed by developing a soft, high‐density, stretchable electrode grid based on an inert, high‐performance composite material comprising gold‐coated titanium dioxide nanowires embedded in a silicone matrix. The developed grid can resolve high spatiotemporal neural signals from the surface of the cortex in freely moving rats with stable neural recording quality and preserved electrode signal coherence during 3 months of implantation. Due to its flexible and stretchable nature, it is possible to minimize the size of the craniotomy required for placement, further reducing the level of invasiveness. The material and device technology presented herein have potential for a wide range of emerging biomedical applications.     

Cryo‐Transferred Ultrathin and Stretchable Epidermal Electrodes

A simple cryo‐transfer method to fabricate ultrathin, stretchable, and conformal epidermal electrodes based on a combination of silver nanowires (AgNWs) network and elastomeric polymers is developed. This method can temporarily enable the soft elastomers with much higher elastic modulus and dimensional contraction through exploiting their glass‐transition behaviors. During this process, a much higher Von Mises stress can be loaded on AgNWs than usual, and the generated strong grip force can facilitate the complete transfer of AgNWs. Afterward, the thawed AgNWs and elastomer composites quickly recover to their soft state at room temperature. The obtained ultrathin and soft electrode with a thickness of 8.4 µm and transmittance of 90.8% at a sheet resistance of 13.2 Ω sq^?1 can tolerate a stretching strain of 70% and 50 000 repeated bending cycles, which meets rigorous requirements of epidermal applications. The as‐prepared epidermal electrodes are effective and comfortable for electrophysiological signal monitoring, and while showing excellent performance exceeding the commercialized gel electrodes.     

Stretchable and Tunable Microtectonic ZnO‐Based Sensors and Photonics

The concept of realizing electronic applications on elastically stretchable “skins” that conform to irregularly shaped surfaces is revolutionizing fundamental research into mechanics and materials that can enable high performance stretchable devices. The ability to operate electronic devices under various mechanically stressed states can provide a set of unique functionalities that are beyond the capabilities of conventional rigid electronics. Here, a distinctive microtectonic effect enabled oxygen‐deficient, nanopatterned zinc oxide (ZnO) thin films on an elastomeric substrate are introduced to realize large area, stretchable, transparent, and ultraportable sensors. The unique surface structures are exploited to create stretchable gas and ultraviolet light sensors, where the functional oxide itself is stretchable, both of which outperform their rigid counterparts under room temperature conditions. Nanoscale ZnO features are embedded in an elastomeric matrix function as tunable diffraction gratings, capable of sensing displacements with nanometre accuracy. These devices and the microtectonic oxide thin film approach show promise in enabling functional, transparent, and wearable electronics.     

Semiconducting Nanowire‐Based Optoelectronic Fibers

The recent ability to integrate semiconductor‐based optoelectronic functionalities within thin fibers is opening intriguing opportunities for flexible electronics and advanced textiles. The scalable integration of high‐quality semiconducting devices within functional fibers however remains a challenge. It is difficult with current strategies to combine high light absorption, good microstructure and efficient electrical contact. The growth of semiconducting nanowires is a great tool to control crystal orientation and ensure a combination of light absorption and charge extraction for efficient photodetection. Thus far, however, leveraging the attributes of nanowires has remained seemingly incompatible with fiber materials, geometry, and processing approaches. Here, the integration of semiconducting nanowire‐based devices at the tip and along the length of polymer fibers is demonstrated for the first time. The scalable thermal drawing process is combined with a simple sonochemical treatment to grow nanowires out of electrically addressed amorphous selenium domains. First principles density‐functional theory calculations show that this approach enables to tailor the surface energy of crystal facets and favors nanowire growth along a preferred orientation, resulting in fiber‐integrated devices of unprecedented performance. This novel platform is exploited to demonstrate an all‐fiber‐integrated fluorescence imaging system, highlighting novel opportunities in sensing, advanced optical probes, and smart textiles.     

Stretchable Light‐Emitting Diodes with Organometal‐Halide‐Perovskite–Polymer Composite Emitters

Intrinsically stretchable light‐emitting diodes (LEDs) are demonstrated using organometal‐halide‐perovskite/polymer composite emitters. The polymer matrix serves as a microscale elastic connector for the rigid and brittle perovskite and induces stretchability to the composite emissive layers. The stretchable LEDs consist of poly(ethylene oxide)‐modified poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate as a transparent and stretchable anode, a perovskite/polymer composite emissive layer, and eutectic indium–gallium as the cathode. The devices exhibit a turn‐on voltage of 2.4 V, and a maximum luminance intensity of 15 960 cd m^?2 at 8.5 V. Such performance far exceeds all reported intrinsically stretchable LEDs based on electroluminescent polymers. The stretchable perovskite LEDs are mechanically robust and can be reversibly stretched up to 40% strain for 100 cycles without failure.     

Stretchable,Electrochemically-Stable Electrochromic Devices Based on Semi-Embedded Ag@Au Nanowire Network

Stretchable electrochromic (EC) devices that can adapt the irregular and dynamic human surfaces show promising applications in wearable display, adaptive camouflage, and visual sensation. However, challenges exist in lacking transparent conductive electrodes with both tensile and electrochemical stability to assemble the complex device structure and endure harsh electrochemical redox reactions. Herein, a wrinkled, semi-embedded Ag@Au nanowire (NW) networks are constructed on elastomer substrates to fabricate stretchable, electrochemically-stable conductive electrodes. The stretchable EC devices are then fabricated by sandwiching a viologen-based gel electrolyte between two conductive electrodes with the semi-embedded Ag@Au NW network. Because the inert Au layer inhibits the oxidation of Ag NWs, the EC device exhibits much more stable color changes between yellow and green than those with pure Ag NW networks. In addition, since the wrinkled semi-embedded structure is deformable and reversibly stretched without serious fractures, the EC devices still maintain excellent color-changing stability under 40% stretching/releasing cycles.