Graphene-enhanced raman spectroscopy reveals the controlled photoreduction of nitroaromatic compound on oxidized graphene surface

Although graphene-enhanced Raman spectroscopy has been investigated for several years, there have been no studies that have applied it to real-time observations of chemical catalytic reactions. Here, we report that UV/ozone-treated oxidized graphene was used to both control and monitor the photoreduction of an adsorbed nitroaromatic dye compound. Graphene-enhanced Raman spectroscopy studies show that more oxidized graphene surface leads to faster photoreduction. This is due to the lowering of the Fermi level in the oxidized graphene, which is in agreement with the highest occupied molecular orbital level of the adsorbed dye molecule, leading to a rapid electron transfer from graphene to the dye. Our findings will be useful in understanding and exploiting the photocatalytic properties of oxidized graphene on adsorbed molecular species.

Optical Probing of Electronic Interaction between Graphene and Hexagonal Boron Nitride

Even weak van der Waals (vdW) adhesion between two-dimensional solids may perturb their various materials properties owing to their low dimensionality. Although the electronic structure of graphene has been predicted to be modified by the vdW interaction with other materials, its optical characterization has not been successful. In this report, we demonstrate that Raman spectroscopy can be utilized to detect a few % decrease in the Fermi velocity (vF) of graphene caused by the vdW interaction with underlying hexagonal boron nitride (hBN). Our study also establishes Raman spectroscopic analysis which enables separation of the effects by the vdW interaction from those by mechanical strain or extra charge carriers. The analysis reveals that spectral features of graphene on hBN are mainly affected by change in vF and mechanical strain, but not by charge doping unlike graphene supported on SiO2 substrates. Graphene on hBN was also found to be less susceptible to thermally induced hole doping.Comment: 19 pages, 4 figure

Thermal Effects of Microwave Reduced-Graphene-Oxide Coated Polyester Fabric on a Simulated Human Skin in Cool and Neutral Air Temperatures

Batteryless wearable technology has wide applications. In particular, human body surface temperature controlling fabrics can help regulate skin temperature in heat or cold. This study investigated surface temperature distribution of the fabrics coated with reduced graphene oxide (rGO) on simulated human body skin conditions at 18 degrees C (cool) and 27 degrees C (neutral) ambient air temperatures. Polyester fabrics were spin-coated with a graphene-oxide (GO) solution of 0.2 wt%. Preparation of rGO was processed by using a microwave oven (MW-rGO). Non-treated fabric (CON) was compared to GO and MW-rGO. The surface temperature of a hot plate was maintained at 35 degrees C or 40 degrees C. The test fabrics were put on the heated hot plate or non-heated-outer portions of the hot plate. Surface temperatures of MW-rGO on the heated hot plate at an air temperature of 18 degrees C (cool) were higher than those of non-treated fabric (CON) under the same conditions (p < 0.01). No effects from the graphene treatment were found on non-heated portions of the graphene oxide fabric (GO) or the reduced graphene oxide fabric (MW-rGO). On the non-heated portions, surface temperatures were higher at the location closer to the hot plate compared to the location farther from the hot plate (p < 0.05). These results partially represent thermal effects of MW-rGO under a specific environment and heat source. Our findings enable an application of reduced graphene oxide to body temperature regulating clothing.

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 plasmaenhanced chemical vapour deposition (PECVD) as photo-blocking layers in the a-IGZO thin film transistors (TFTs). The charge mobility and threshold voltage (V-th) of the TFTs depend on the thickness of the Si-Ge films and dielectric buffer layers (SiNX), which were carefully optimized to be similar to 200 nm and similar to 300 nm, respectively. As a result, even after 1,000 s illumination time, the V-th 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.

Transport properties of graphene with one-dimensional charge defects

We study the effect of extended charge defects in electronic transport properties of graphene. Extended defects are ubiquitous in chemically and epitaxially grown graphene samples due to internal strains associated with the lattice mismatch. We show that at low energies these defects interact quite strongly with the 2D Dirac fermions and have an important effect in the DC-conductivity of these materials.Comment: 6 pages, 5 figures. published version: one figure, appendix and references adde

Graphene for Controlled and Accelerated Osteogenic Differentiation of Human Mesenchymal Stem Cells

Modern tissue engineering strategies combine living cells and scaffold materials to develop biological substitutes that can restore tissue functions. Both natural and synthetic materials have been fabricated for transplantation of stem cells and their specific differentiation into muscles, bones and cartilages. One of the key objectives for bone regeneration therapy to be successful is to direct stem cells' proliferation and to accelerate their differentiation in a controlled manner through the use of growth factors and osteogenic inducers. Here we show that graphene provides a promising biocompatible scaffold that does not hamper the proliferation of human mesenchymal stem cells (hMSCs) and accelerates their specific differentiation into bone cells. The differentiation rate is comparable to the one achieved with common growth factors, demonstrating graphene's potential for stem cell research.Comment: 34 pages, 11 figures, 1 table, submitte

Roles of T follicular helper cells and T follicular regulatory cells in Autoantibody Production in IL-2-deficient mice

Autoantibodies can result from excessive T follicular helper (Tfh) cell activity, whereas T follicular regulatory (Tfr) cells negatively regulate autoantibody production. IL-2 knockout (KO) mice on the BALB/c background have elevated Tfh responses, produce autoantibodies, and develop lethal autoimmunity. We analyzed Tfh and Tfr cells in IL-2 KO mice on the C57BL/6 (B6) genetic background. In B6 IL-2 KO mice, the spontaneous formation of Tfh cells and germinal center B cells was greatly enhanced, along with production of anti-DNA autoantibodies. IL-2 has been reported to repress Tfr cell differentiation; however, Tfr cells were not increased over wild-type levels in the B6 IL-2 KO mice. To assess Tfh and Tfr cell regulation of autoantibody production in IL-2 KO mice, we generated IL-2 KO mice with a T cell-specific deletion of the master Tfh cell transcription factor Bcl6. In IL-2 KO Bcl6 conditional KO (2KO-Bcl6TC) mice, Tfh cells, Tfr cells, and germinal center B cells were ablated. In contrast to expectations, autoantibody IgG titers in 2KO-Bcl6TC mice were significantly elevated over autoantibody IgG titers in IL-2 KO mice. Specific deletion of Tfr cells with Foxp3-cre Bcl6-flox alleles in IL-2 KO mice led to early lethality, before high levels of autoantibodies could develop. We found IL-2+/+ Tfr cell-deficient mice produce significant levels of autoantibodies. Our overall findings provide evidence that Tfh cells are dispensable for high-level production of autoantibodies and also reveal a complex interplay between Tfh and Tfr cells in autoantibody production and autoimmune disease