Photoinitiated Polymerization of Hydrogels by Graphene Quantum Dots.

As a smart stimulus-responsive material, hydrogel has been investigated extensively in many research fields. However, its mechanical brittleness and low strength have mattered, and conventional photoinitiators used during the polymerization steps exhibit high toxicity, which limits the use of hydrogels in the field of biomedical applications. Here, we address the dual functions of graphene quantum dots (GQDs), one to trigger the synthesis of hydrogel as photoinitiators and the other to improve the mechanical strength of the as-synthesized hydrogel. GQDs embedded in the network effectively generated radicals when exposed to sunlight, leading to the initiation of polymerization, and also played a significant role in improving the mechanical strength of the crosslinked chains. Thus, we expect that the resulting hydrogel incorporated with GQDs would enable a wide range of applications that require biocompatibility as well as higher mechanical strength, including novel hydrogel contact lenses and bioscaffolds for tissue engineering.

Silicon germanium photo-blocking layers for a-IGZO based industrial display.

Amorphous indium- gallium-zinc oxide (a-IGZO) has been intensively studied for the application to active matrix flat-panel display because of its superior electrical and optical properties. However, the characteristics of a-IGZO were found to be very sensitive to external circumstance such as light illumination, which dramatically degrades the device performance and stability practically required for display applications. Here, we suggest the use for silicon-germanium (Si-Ge) films grown plasma-enhanced chemical vapour deposition (PECVD) as photo-blocking layers in the a-IGZO thin film transistors (TFTs). The charge mobility and threshold voltage (Vth) of the TFTs depend on the thickness of the Si-Ge films and dielectric buffer layers (SiNX), which were carefully optimized to be ~200 nm and ~300 nm, respectively. As a result, even after 1,000 s illumination time, the Vth and electron mobility of the TFTs remain unchanged, which was enabled by the photo-blocking effect of the Si-Ge layers for a-IGZO films. Considering the simple fabrication process by PECVD with outstanding scalability, we expect that this method can be widely applied to TFT devices that are sensitive to light illumination.

Large-scale transfer-free growth of thin graphite films at low temperature for solid diffusion barriers.

Amorphous indium-gallium-zinc oxide (a-IGZO) thin-film transistors (TFTs) have been under intense investigation as one of the promising candidates for active matrix flat-panel displays. However, solid diffusion of a-IGZO to other layers during TFT device fabrication highly degrades their electrical and optical properties. It is expected that the diffusion-impenetrable properties of graphitic materials can be utilized as diffusion barriers. A conventional transfer method and direct growth on TFTs with high temperature are limited due to wet transfer conditions and low Tg (∼540 °C) of the glass substrates, respectively. Here we report the large-scale transfer-free growth of thin graphite films at low temperature (∼350 °C) for solid diffusion barriers in the a-IGZO TFTs using plasma enhanced chemical vapor deposition (PECVD), which can be widely used to protect solid-diffusion for sustainable and scalable future industrial technology.

Roll-to-Roll Laser-Printed Graphene-Graphitic Carbon Electrodes for High-Performance Supercapacitors.

Carbon electrodes including graphene and thin graphite films have been utilized for various energy and sensor applications, where the patterning of electrodes is essentially included. Laser scribing in a DVD writer and inkjet printing were used to pattern the graphene-like materials, but the size and speed of fabrication has been limited for practical applications. In this work, we devise a simple strategy to use conventional laser-printer toner materials as precursors for graphitic carbon electrodes. The toner was laser-printed on metal foils, followed by thermal annealing in hydrogen environment, finally resulting in the patterned thin graphitic carbon or graphene electrodes for supercapacitors. The electrochemical cells made of the graphene-graphitic carbon electrodes show remarkably higher energy and power performance compared to conventional supercapacitors. Furthermore, considering the simplicity and scalability of roll-to-roll (R2R) electrode patterning processes, the proposed method would enable cheaper and larger-scale synthesis and patterning of graphene-graphitic carbon electrodes for various energy applications in the future.