Ultraflexible and transparent electroluminescent skin for real-time and super-resolution imaging of pressure distribution.

The ability to image pressure distribution over complex three-dimensional surfaces would significantly augment the potential applications of electronic skin. However, existing methods show poor spatial and temporal fidelity due to their limited pixel density, low sensitivity, or low conformability. Here, we report an ultraflexible and transparent electroluminescent skin that autonomously displays super-resolution images of pressure distribution in real time. The device comprises a transparent pressure-sensing film with a solution-processable cellulose/nanowire nanohybrid network featuring ultrahigh sensor sensitivity (>5000 kPa-1) and a fast response time (<1 ms), and a quantum dot-based electroluminescent film. The two ultrathin films conform to each contact object and transduce spatial pressure into conductivity distribution in a continuous domain, resulting in super-resolution (>1000 dpi) pressure imaging without the need for pixel structures. Our approach provides a new framework for visualizing accurate stimulus distribution with potential applications in skin prosthesis, robotics, and advanced human-machine interfaces.

Facile extraction of cellulose nanocrystals.

A simple process for extracting cellulose nanocrystals (CNCs) is proposed that only uses high-pressure homogenization (HPH) controlling a process temperature. The proposed process was assessed and compared with normal production through acidic hydrolysis. Temperature-controlled HPH produced CNCs with high crystallinity, which linearly increased with increasing process temperature over 20 passes. The CNCs had uniform widths and lengths in the ranges of 4-14 nm and 60-320 nm, respectively. Undesirable chemical reaction can be avoided with the proposed process because no chemical was used to promote the CNC extraction. This method is an efficient and sustainable green approach to CNC production.

Snow-Ice-Inspired Approach for Growth of Amorphous Silicon Nanotips.

The growth of one-dimensional nanostructures without a metal catalyst via a simple solution method is of considerable interest due to its practical applications. In this study, the growth of amorphous silicon (a-Si) nanotips was investigated using an aqueous solution dropped onto the Si substrate, followed by drying at room temperature or below for 24 h, resulting in the formation of a-Si nanotips on the Si substrate. Typically, the a-Si nanotips were up to 1.6 µm long, with average top and middle diameters of 30 and 80 nm, respectively, and contained no metal catalyst in their structure. The growth of a-Si nanotips can be explained in terms of the liquid-solid mechanism, where the supercritical Si solution (liquid) generated on the Si substrate (after reaction with the aqueous solution) promotes the nucleation of solid Si (acting as seeds) on the roughened surface, followed by surface diffusion of Si atoms along the side wall of the Si seeds. This is very similar to the phenomenon observed in the growth of snow ice crystals in nature. When photoexcited at 265 nm, the a-Si nanotips showed blue luminescence at around 435 nm (2.85 eV), indicating feasible applicability of the nanotips in optoelectronic functional devices.

Self-Powered Motion-Driven Triboelectric Electroluminescence Textile System.

In recent years, smart light-emitting-type electronic devices for wearable applications have been required to have flexibility and miniaturization, which limits the use of conventional bulk batteries. Therefore, it is important to develop a self-powered light-emitting system. Our study demonstrates the potential of a new self-powered luminescent textile system that emits light driven by random motions. The device is a ZnS:Cu-based textile motion-driven electroluminescent device (TDEL) fabricated onto the woven fibers of a ZnS:Cu-embedded PDMS (polydimethylsiloxane) composite. Triboelectrification, which raises a discontinuous electric field, is generated by the contact separation movement of the friction material. Therefore, light can be generated via triboelectrification by the mechanical deformation of the ZnS:Cu-embedded PDMS composite. This study showed that the TDEL emitted light from the internal triboelectric field during contact and from the external triboelectric field during separation. Light was then emitted twice in a cycle, suggesting that continuous light can be emitted by various movements, which is a key step in developing self-powered systems for wearable applications. Therefore, this technology is a textile motion-driven electroluminescence system based on composite fibers (ZnS:Cu + PDMS) and PTFE fibers, and the proposed self-emitting textile system can be easily fabricated and applied to smart clothes.

Photolithography-Based Patterning of Liquid Metal Interconnects for Monolithically Integrated Stretchable Circuits.

We demonstrate a new patterning technique for gallium-based liquid metals on flat substrates, which can provide both high pattern resolution (∼20 µm) and alignment precision as required for highly integrated circuits. In a very similar manner as in the patterning of solid metal films by photolithography and lift-off processes, the liquid metal layer painted over the whole substrate area can be selectively removed by dissolving the underlying photoresist layer, leaving behind robust liquid patterns as defined by the photolithography. This quick and simple method makes it possible to integrate fine-scale interconnects with preformed devices precisely, which is indispensable for realizing monolithically integrated stretchable circuits. As a way for constructing stretchable integrated circuits, we propose a hybrid configuration composed of rigid device regions and liquid interconnects, which is constructed on a rigid substrate first but highly stretchable after being transferred onto an elastomeric substrate. This new method can be useful in various applications requiring both high-resolution and precisely aligned patterning of gallium-based liquid metals.

Effect of Inductively Coupled Plasma on the Structural and Electrical Properties of Ti-Doped ITO Films Formed by IPVD.

In this study, we investigated Ti-doped ITO films formed through ionized physical vapor deposition (IPVD) using inductively coupled plasma (ICP). Ti-doped ITO thin films showed an enhanced mobility with ICP power; owing to the improved crystallinity, and the sheet resistance of the Ti-doped ITO (30 nm) largely decreased from 295.1 to 134.5 ohm/sq, even during at room temperature. Therefore, IPVD technology offers a useful tool for transparent electrodes with a large area window-unified touch-screen panel.

Index-matched indium tin oxide electrodes for capacitive touch screen panel applications.

Index-matched indium tin oxide (ITO) electrodes for capacitive touch screen panels have been fabricated to improve optical transmittance and reduce the difference of reflectance (deltaR) between the etched and un-etched regions. 8.5 nm Nb2O5 and 49 nm SiO2 thin films were deposited by magnetron sputtering as index-matching layers between an ITO electrode and a glass substrate. In case of 30 nm ITO electrode, a 4.3% improvement in the optical transmittance and a deltaR of less than 1% were achieved, along with a low sheet resistance of 90 omega/square.

In situ-grown hexagonal silicon nanocrystals in silicon carbide-based films.

Silicon nanocrystals (Si-NCs) were grown in situ in carbide-based film using a plasma-enhanced chemical vapor deposition method. High-resolution transmission electron microscopy indicates that these nanocrystallites were embedded in an amorphous silicon carbide-based matrix. Electron diffraction pattern analyses revealed that the crystallites have a hexagonal-wurtzite silicon phase structure. The peak position of the photoluminescence can be controlled within a wavelength of 500 to 650 nm by adjusting the flow rate of the silane gas. We suggest that this phenomenon is attributed to the quantum confinement effect of hexagonal Si-NCs in silicon carbide-based film with a change in the sizes and emission states of the NCs.

Nanocrystalline ZnO film layer on silicon and its application to surface acoustic wave-based streaming.

A surface acoustic wave (SAW) device consisting of 1-6 microm-thick ZnO thin films deposited on Si wafer was designed, fabricated, and characterized in this study. Photolithographic protocols for interdigitated transducers (IDTs) and surface modification using fluoroalkylsilane are employed with the aim of droplet-based microfluidic actuations in bio-microsystems. A ZnO thin film was grown on a 4' silicon wafer with c-axis orientation, an average roughness of 11.6 nm, and a small grain size of 20 nm. It was found that the resonant frequencies (Rayleigh and Sezawa modes) of SAW devices move to a lower frequency range as the thickness of the ZnO thin films increases. Through the silane surface modification, a hydrophobic surface with a contact angle of 114 degrees was obtained. Finally, liquid streaming by acoustic wave was demonstrated by observing the actuation of SiO2 microparticles in a microfluidic drop.