Deformable Organic Nanowire Field‐Effect Transistors

Deformable electronic devices that are impervious to mechanical influence when mounted on surfaces of dynamically changing soft matters have great potential for next‐generation implantable bioelectronic devices. Here, deformable field‐effect transistors (FETs) composed of single organic nanowires (NWs) as the semiconductor are presented. The NWs are composed of fused thiophene diketopyrrolopyrrole based polymer semiconductor and high‐molecular‐weight polyethylene oxide as both the molecular binder and deformability enhancer. The obtained transistors show high field‐effect mobility >8 cm² V^?1 s^?1 with poly(vinylidenefluoride‐ co ‐trifluoroethylene) polymer dielectric and can easily be deformed by applied strains (both 100% tensile and compressive strains). The electrical reliability and mechanical durability of the NWs can be significantly enhanced by forming serpentine‐like structures of the NWs. Remarkably, the fully deformable NW FETs withstand 3D volume changes (>1700% and reverting back to original state) of a rubber balloon with constant current output, on the surface of which it is attached. The deformable transistors can robustly operate without noticeable degradation on a mechanically dynamic soft matter surface, e.g., a pulsating balloon (pulse rate: 40 min^?1 (0.67 Hz) and 40% volume expansion) that mimics a beating heart, which underscores its potential for future biomedical applications.     

High‐Performance Triboelectric Nanogenerators Based on Electrospun Polyvinylidene Fluoride–Silver Nanowire Composite Nanofibers

The preparation of ferroelectric polymer–metallic nanowire composite nanofiber triboelectric layers is described for use in high‐performance triboelectric nanogenerators (TENGs). The electrospun polyvinylidene fluoride (PVDF)–silver nanowire (AgNW) composite and nylon nanofibers are utilized in the TENGs as the top and bottom triboelectric layers, respectively. The electrospinning process facilitates uniaxial stretching of the polymer chains, which enhances the formation of the highly oriented crystalline β‐phase that forms the most polar crystalline phase of PVDF. The addition of AgNWs further promotes the β‐phase crystal formation by introducing electrostatic interactions between the surface charges of the nanowires and the dipoles of the PVDF chains. The extent of β‐phase formation and the resulting variations in the surface charge potential upon the addition of nanowires are systematically analyzed using X‐ray diffraction (XRD) and Kelvin probe force microscopy techniques. The ability of trapping the induced tribocharges increases upon the addition of nanowires to the PVDF matrix. The enhanced surface charge potential and the charge trapping capabilities of the PVDF–AgNW composite nanofibers significantly enhance the TENG output performances. Finally, the mechanical stability of the electrospun nanofibers is dramatically enhanced while maintaining the TENG performances by applying thermal welding near the melting temperature of PVDF.     

Colloidal synthesis of ultrathin two-dimensional semiconductor nanocrystals

2D semiconductor quantum wells have been recognized as potential candidates for various quantum devices. In quantum wells, electrons and holes are spatially confined within a finite thickness and freely move in 2D space. Much effort has focused on shape control of colloidal semiconductor nanocrystals(NCs), and synthesis of 2D colloidal NCs has been achieved very recently. Here, recent advances in colloidal synthesis of uniform and ultrathin 2D CdSeNCs are highlighted. Structural and optical property characterization of these quantum-sized 2D CdSe NCs is discussed. Additionally, 2D CdSe NCs doped with Mn 2+ ions for dilute magnetic semiconductors (DMS) are presented.These 2D CdSe-based NCs can be used as model systems for studying quantum-well structures.     

Flexible/Stretchable Supercapacitors with Novel Functionality for Wearable Electronics

With the miniaturization of personal wearable electronics, considerable effort has been expended to develop high-performance flexible/stretchable energy storage devices for powering integrated active devices. Supercapacitors can fulfill this role owing to their simple structures, high power density, and cyclic stability. Moreover, a high electrochemical performance can be achieved with flexible/stretchable supercapacitors, whose applications can be expanded through the introduction of additional novel functionalities. Here, recent advances in and future prospects for flexible/stretchable supercapacitors with innate functionalities are covered, including biodegradability, self-healing, shape memory, energy harvesting, and electrochromic and temperature tolerance, which can contribute to reducing e-waste, ensuring device integrity and performance, enabling device self-charging following exposure to surrounding stimuli, displaying the charge status, and maintaining the performance under a wide range of temperatures. Finally, the challenges and perspectives of high-performance all-in-one wearable systems with integrated functional supercapacitors for future practical application are discussed.     

Stress Relief Principle of Micron‐Sized Anodes with Large Volume Variation for Practical High‐Energy Lithium‐Ion Batteries

Practical applications of high gravimetric and volumetric capacity anodes for next‐generation lithium‐ion batteries have attracted unprecedented attentions, but still faced challenges by their severe volume changes, rendering low Coulombic efficiency and fast capacity fading. Nano and void‐engineering strategies had been extensively applied to overcome the large volume fluctuations causing the continuous irreversible reactions upon cycling, but they showed intrinsic limit in fabrication of practical electrode condition. Achieving high electrode density is particularly paramount factor in terms of the commercial feasibility, which is mainly dominated by the true density and tapping density of active material. Herein, based on finite element method calculation, micron‐sized double passivation layered Si/C design is introduced with restrictive lithiation state, which can withstand the induced stress from Li insertion upon repeated cycling. Such design takes advantage in structural integrity during long‐term cycling even at high gravimetric capacity (1400 mAh g^?1). In 1 Ah pouch‐type full‐cell evaluation with high mass loading and electrode density (≈3.75 mAh cm^?2 and ≈1.65 g cm^?3), it demonstrates superior cycle stability without rapid capacity drop during 800 cycles.     

Graphene: Materials to devices (invited)

Despite recent progress in understanding geometric structure, electronic structure, and transport properties in a graphene device (GD), role of point defects, edges, traps in a GD or a gate insulator has been poorly defined. We have studied electronic and geometric structures of these defects using scanning probe microscopy and try to link those with the transport properties of the GD. We perform scanning gate microscopy study to understand the local carrier scattering. It was found that geometric corrugations, defects and edges directly influence the local transport current. This observation is linked directly with a proposed scattering model based on macroscopic transport measurements. We suggest that dangling bonds in insulator-material SiO₂ mainly used in GDs produce charge puddles and they work as scattering centers.     

Resistive switching characteristics and conducting nanobits of polycrystalline NiO thin films

Thin films of NiO were deposited on Pt/Ta/glass sub-strates using a radio frequency (RF) sputtering method. The NiO thin films showed polycrystalline nature, indicating preferentially (111)-oriented structure. The resistive random access memory (RRAM) capacitor of a Pt/NiO/Pt structure exhibited unipolar switching characteristics and bistable resistivities for 200 repeated switching cycles. Furthermore, RRAM nanobits array was formed on the NiO thin films by applying a bias. The RRAM nanobits had a diameter of approximately 8 nm and were observed via a conducting atomic force microscope (CAFM). The density of the RRAM nanobits array was estimated to be approximately 0.64 Tbit/cm².     

Improvement strategy for edge waviness in roll bending process of corrugated sheet metals

This paper focuses on the corrugated thin-walled sheet metal in the roll bending process. The main defect that appears in corrugated panels subjected to high amounts of bending deformation is a wavy edge. Edge defects are caused by excessive longitudinal stress and strain near the edge of the plate, and local edge buckling may occur when some critical value of the bending radius is exceeded. This paper proposes two different approaches to avoid a wavy edge for a formed panel: excessive stress on the edge region is restrained by controlling the length of the cross-sectional end of the corrugated panel while considering the stress distribution, and the bending radius in each forming step is determined by considering the strain limit at which the initial edge waviness occurs to avoid excessive compression at particular steps. The experimental and numerical results indicated that the two proposed design strategies can minimize wavy edges in the formed shape.     

Stomata‐Inspired Photomechanical Ion Nanochannels Modified by Azobenzene Composites

A low‐powered and highly selective photomechanical sensor system mimicking stomata in the epidermis of leaves harvested from nature is demonstrated. This device uses a light‐responsive composite consisting of 4‐amino‐1,1′‐azobenzene‐3,4′‐disulfonic acid monosodium salt (AZO) and poly(diallyldimethylammonium chloride) (PDDA) coated on a membrane with tens of nanometer‐size pores. The ionic current change through the pore channels as a function of pore size variation is then measured. The tran–cis isomerism of AZO–PDDA during light irradiation and the operation mechanism of photomechanical ion channel sensor are discussed and analyzed using UV–vis spectroscopy and atomic force microscopy analysis. It presents the discriminative current levels to the different light wavelengths. The response time of the photoreceptor is about 0.2 s and it consumes very low operating power (≈15 nW) at 0.1 V bias. In addition, it is found that the change of the pore diameter during the light irradiation is due to the photomechanical effect, which is capable of distinguishing light intensity and wavelength.     

Temperature Control of a Regasification System for LNG-fuelled Marine Engines Using Nonlinear Control Techniques

International Journal of Control, Automation and Systems - This paper presents two nonlinear PID (NPID) controllers which control the glycol temperature of a regasification system for LNG-fuelled...