Nyan-Hwa Tai

Superhydrophobic and superoleophilic properties of graphene-based sponges fabricated using a facile dip coating method

Superhydrophobic and superoleophilic graphene-based sponges are demonstrated as efficient absorbents for a broad range of oils and organic solvents with high selectivity, good recyclability, and excellent absorption capacities up to 165 times their own weight. The findings show promise for large-scale removal of organic contaminants, especially in the field of oil spillage cleanup.

Transfer of patterned vertically aligned carbon nanotubes onto plastic substrates for flexible electronics and field emission devices

A direct transfer method for fabricating flexible electronics without the assistance of an adhesive layer and stamp is reported in this paper. This rapid and simple method provides an approach for the application of vertically aligned carbon nanotubes (VA-CNTs) on plastic substrates. After transfer, the VA-CNTs maintained their initial orientation in the designed pattern and showed sufficient adhesion to the substrate under extreme bending conditions. The flexible device performed an emission on the transparent substrate and showed a low turn-on of 1.13 V/μm. This VA-CNT-based flexible device, which exhibits electrical resistance sensitive to bending, is also described herein.

Carbon materials as oil sorbents: a review on the synthesis and performance

Oil spill accidents have urged scientists across the world to develop an immediate cleanup technology because the spilled oil significantly affects the ecological and environmental system. Superhydrophobic and superoleophilic materials have shown potential application in the field of oil spill cleanup due to their outstanding absorption capabilities, high selectivity, chemical inertness and excellent recyclability. In this regard, carbon-based absorbents have been considered to be the best candidates as they possess high surface area, low density, excellent mechanical properties, good chemical stability, environmental friendliness and large pore volume. Carbon aerogels, graphene or carbon nanotubes (CNTs) coated sponges, carbon nanotube forests, graphene foams or sponges, carbon coatings, activated carbon, porous carbon nanoparticles and carbon fibers have been widely investigated for water filtration, water/oil separation, oil-spill cleanup, wastewater treatment, gas separation and purification. In this paper, the synthesis, applications and reusability of these carbon-based absorbents have been reviewed and their performances compared.

Origin of a needle-like granular structure for ultrananocrystalline diamond films grown in a N2/CH4 plasma

Microstructural evolution as a function of substrate temperature (TS) for conducting ultrananocrystalline diamond (UNCD) films is systematically studied. Variation of the sp2 graphitic and sp3 diamond content with TS in the films is analysed from the Raman and near-edge x-ray absorption fine structure spectra. Morphological and microstructural studies confirm that at TS = 700 °C well-defined acicular structures evolve. These nanowire structures comprise sp3 phased diamond, encased in a sheath of sp2 bonded graphitic phase. TS causes a change in morphology and thereby the various properties of the films. For TS = 800 °C the acicular grain growth ceases, while that for TS = 700 °C ceases only upon termination of the deposition process. The grain-growth process for the unique needle-like granular structure is proposed such that the CN species invariably occupy the tip of the nanowire, promoting an anisotropic grain-growth process and the formation of acicular structure of the grains. The electron field emission studies substantiate that the films grown at TS = 700 °C are the most conducting, with conduction mediated through the graphitic phase present in the films.

Induction and regulation of differentiation in neural stem cells on ultra-nanocrystalline diamond films

The interaction of ultra-nanocrystalline diamond (UNCD) with neural stem cells (NSCs) has been studied in order to evaluate its potential as a biomaterial. Hydrogen-terminated UNCD (H-UNCD) films were compared with standard grade polystyrene in terms of their impact on the differentiation of NSCs. When NSCs were cultured on these substrates in medium supplemented with low concentration of serum and without any differentiating factors, H-UNCD films spontaneously induced neuronal differentiation on NSCs. By direct suppression of mitogen-activated protein kinase/extracellular signaling-regulated kinase1/2 (MAPK/Erk1/2) signaling pathway in NSCs using U0126, known to inhibit the activation of Erk1/2, we demonstrated that the enhancement of Erk1/2 pathway is one of the effects of H-UNCD-induced NSCs differentiation. Moreover, functional-blocking antibody directed against integrin beta1 subunit inhibited neuronal differentiation on H-UNCD films. This result demonstrated the involvement of integrin beta1 in H-UNCD-mediated neuronal differentiation. Mechanistic studies revealed the cell adhesion to H-UNCD films associated with focal adhesion kinase (Fak) and initiated MAPK/Erk1/2 signaling. Our study demonstrated that H-UNCD films-mediated NSCs differentiation involves fibronectin-integrin beta1 and Fak-MAPK/Erk signaling pathways in the absence of differentiation factors. These observations raise the potential for the use of UNCD as a biomaterial for central nervous system transplantation and tissue engineering.

The effect of ultra-nanocrystalline diamond films on the proliferation and differentiation of neural stem cells

The interaction of ultra-nanocrystalline diamond (UNCD) with neural stem cells (NSCs) has been studied along with its surface modification in order to improve its function as a biomaterial. Hydrogen- and oxygen-terminated UNCD films were compared with standard grade polystyrene in terms of their impact on the growth, expansion and differentiation of NSCs. When NSCs were cultured on these substrates in low serum and without any differentiating factors, hydrogen-terminated UNCD films spontaneously induced cell proliferation and neuronal differentiation. Oxygen-terminated UNCD films were also shown to further improve neural differentiation, with a preference to differentiate into oligodendrocytes. Hence, controlling the surface properties of UNCD could manipulate the differentiation of NSCs for different biomedical applications. These observations raise the potential for the use of UNCD as a biomaterial for central nervous system transplantation and tissue engineering.

Assessment of ultrasonic drilling of C/SiC composite material

Abstract Ultrasonic drilling of two-dimensional carbon fiber-reinforced silicon carbide(C/SiC) composites was investigated in this study. The composites were made through a polymer pyrolysis route. X-ray diffraction was adopted to examine the formation of crystalline structure in the matrix of the fabricated composites. Density and porosity, and flexural strength were measured to study the densification efficiency and the mechanical properties, respectively, of the C/SiC composites fabricated under various conditions. The fracture morphologies were also examined by scanning electron microscopy to investigate the fracture behavior of the composites under flexural test. The effects of various parameters of ultrasonic drilling, including abrasives, volume ratio, electric current and down-force, on the material removal rate, hole clearance, edge quality and tool wear are presented and discussed. Optimal operating conditions are identified. In comparison with other feasible machining processes, ultrasonic drilling for this composite material possesses advantages concerning machinability and cost.

Enhancing the Electrical Conductivity of Carbon-Nanotube-Based Transparent Conductive Films Using Functionalized Few-Walled Carbon Nanotubes Decorated with Palladium Nanoparticles as Fillers

This work demonstrates the processing and characterization of the transparent and highly electrically conductive film using few-walled carbon nanotubes (FWCNTs) decorated with Pd nanoparticles as fillers. The approach included functionalizing the FWCNTs, immersing them in an aqueous solution of palladate salts, and subsequently subjecting them to a reduction reaction in H(2). Field-emission scanning electron microscopy and transmission electron microscopy images showed that the functionalized FWCNTs (f-FWCNTs) were decorated with uniform and homogeneous Pd nanoparticles with an average diameter of 5 nm. A shift of the G-band to a higher frequency in the Raman spectra of the Pd-decorated f-FWCNTs (Pd@f-FWCNTs) illustrates that the p-type doping effect was enhanced. X-ray photoelectron spectroscopy and energy-dispersive X-ray spectroscopy showed that PdCl(2) was the primary decoration compound on the f-FWCNTs prior to the reduction reaction and that Pd nanoparticles were the only decorated nanoparticles after H(2) reduction. The contact resistance between the metallic materials and the semiconducting CNTs in FWCNTs, controlled by the Schottky barrier, was significantly decreased compared to the pristine FWCNTs. The decrease in contact resistance is attributed to the 0.26 eV increase of the work function of the Pd@f-FWCNTs. Extremely low sheet resistance of 274 ohm/sq of the poly(ethylene terephthalate) substrates coated with Pd@f-FWCNTs was attained, which was 1/25 the resistance exhibited by those coated with FWCNTs, whereas the same optical transmittance of 81.65% at a wavelength of 550 nm was maintained.

Synthesis of ethanol-soluble few-layer graphene nanosheets for flexible and transparent conducting composite films

We report a facile method of preparing few-layer graphene nanosheets (FLGs), which can be soluble in ethanol. Atomic force microscopy and high-resolution transmission electron microscopy studies reveal that FLGs have average thicknesses in the range of 2.6-2.8 nm, corresponding to 8-9 layers. A graphene/nafion composite film has a sheet resistance of 9.70 kΩ/sq at the transmittance of 74.5% (at 550 nm) while the nafion film on polyethylene terephthalate has a sheet resistance of 128 kΩ/sq at transmittance of 90.0%. For the cycling/bending test, almost no change in resistance was exhibited when the film was bent at an angle up to 140°, and no obvious deviation in resistance could be found after 100 bending cycles was applied. In addition, an FLGs-poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) composite layer was demonstrated as the effective hole transporting layer to improve the hole transporting ability in an organic photovoltaic device, with which the power conversion efficiency was enhanced from 3.10% to 3.70%. The results demonstrated the promising applications of FLGs on graphene-based electronics, such as transparent electrode and flexible conducting film.

Field emission properties of carbon nanotube arrays through the pattern transfer process

A process for transferring carbon nanotube (CNT) arrays from a silicon wafer to an alumina substrate coated with Ag paste is proposed. A current density of up to 325?mA?cm?2 at an electric field of 2.4?V??m?1 was achieved. The influence of the patterned size and the length of carbon nanotubes on the field emission properties were investigated. Through this transfer method, the adhesion between the CNTs and the substrate is enhanced and the current density and turn-on voltage are improved. The effects of the microstructure of the emitting sites at the CNT tip on the current density were also studied.