Therefore, surface instability is a significant problem for flexible transparent electrodes and electronics that require high optical transmittance and a flat surface, [16,17] and it is of great importance to design stretchable electrodes free of surface instabilities. However, flexible electrodes, as well as flexible devices, are required to be employed under various mechanical modes including bending, compression, twisting, stretching, or being subjected to prestrain in order to improve their stretchability, and all of these deformation modes induce anisotropic compressive strains that can easily exceed the critical wrinkling strain and thereby generate surface instabilities. For example, uniaxial stretching generates tension along the elongation direction, whereas in the perpendicular direction the smaller Poisson's ratio of the top conducting layers will lead to a smaller lateral contraction than that of the substrate, thereby causing in-plane compressive stresses and surface instabilities in the top layers. [18] Therefore, the flexible electronics community urgently needs a strategy that can prevent surface instabilities in flexible or stretchable bi/multilayered electrodes and devices, as well as find novel structure designs for wearable and biocompatible flexible devices. [19][20][21] In this study, we describe a general design strategy to achieve wrinkle-free stretchable electrodes and devices by introducing a network structure with a large Poisson's effect into The next generation of flexible electronics will require highly stretchable and transparent electrodes, many of which consist of a relatively stiff metal network (or carbon materials) and an underlying soft substrate. Typically, such a stiff-soft bilayer suffers from wrinkling or folding when subjected to strains, causing high surface roughness and seriously deteriorated optical transparency. In this work, a network with a giant effective Poisson's ratio on a soft substrate is found to be under biaxial tension upon deformation, and thus does not wrinkle or fold, but maintains smooth surfaces and high transparency. Soft tactile sensors employing such network electrodes exhibit high transparency and low fatigue over many stretching cycles. Such a giant Poisson's ratio has the same effect in other systems. This work offers a new understanding of surface instabilities and a general strategy to prevent them not only in flexible electronics, but also in other materials and mechanical structures that require flat surfaces.

A wearable supercapacitor achieved high transparency of 82.1% and an excellent areal capacitance of 0.53 mF cm−2, together with high stretchability (160% strain).

No abstract

Carbon dots (CDs) based nanomaterials have great potential in a wide range of biomedical areas, including bioimaging, biosensor, and tissue engineering. Thus, it is highly desired to develop novel costeffective, eco-friendly and easy to scale-up fabrication for CDs based nanomaterials for biomedical applications. Herein, we developed a facile synthesis of CDs by a one-step hydrothermal method. The synthesized CDs showed stable photoluminescence, highresolution imaging of live cells and low cytotoxicity. Furthermore, the CDs were prepared to electrospun nanofiber mats (CDs-NFMs), where enough carboxylic acid moieties and hydroxyls on the surface of the nanofibers, leading to excellent biocompatibility and fluorescence property. More importantly, cell proliferation on the CDs-NFMs was much better than that on NFMs without CDs; moreover, CDs-NFMs could also guide cells growth along the nanofibers and enhance the cellular activities, which indicated that the func-tional groups on the surface of the CDs play a critical role in supporting cellular activities. Combining with excellent fluorescence property, we anticipate that this finding greatly enhances great potential applications of CDs for cell culture, tissue engineering as well as other biomedical applications. POLYM. COMPOS., 39:73-80, 2018.

With the progress of wide bandgap semiconductors, compact solid-state light-emitting devices for the ultraviolet wavelength region are of considerable technological interest as alternatives to conventional ultraviolet lamps in recent years. Here, the potential of aluminum nitride (AlN) as an ultraviolet luminescent material was studied. An ultraviolet light-emitting device, equipped with a carbon nanotube (CNT) array as the field-emission excitation source and AlN thin film as cathodoluminescent material, was fabricated. In operation, square high-voltage pulses with a 100 Hz repetition frequency and a 10% duty ratio were applied to the anode. The output spectra reveal a dominant ultraviolet emission at 330 nm with a short-wavelength shoulder at 285 nm, which increases with the anode driving voltage. This work has explored the potential of AlN thin film as a cathodoluminescent material and provides a platform for investigating other ultrawide bandgap (UWBG) semiconductors. Furthermore, while using AlN thin film and a carbon nanotube array as electrodes, this ultraviolet cathodoluminescent device can be more compact and versatile than conventional lamps. It is anticipated to be useful in a variety of applications such as photochemistry, biotechnology and optoelectronics devices.