Tsung-Yen Tsai

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.

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.

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.

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.

Photorefractive effect in nematic-clay nanocomposites.

The orientational photorefractive effect was observed in an organic-inorganic nanocomposite of nematic liquid crystal hybridized with montmorillonite clay. Both the self-diffraction and beam-coupling effects were evaluated in a two-wave-mixing experiment in conjunction with an externally applied dc field. The experimental results indicate that photoinduced generation was enhanced by the addition of smectite clay with adequate concentration. Physically, the drifting ion charges were trapped by clay layers and separated by interlayer cations, creating an internal, spatially modulated space-charge field, which led to nematic molecular orientation and, then, refractive-index modulation via the electro-optical response. The diffraction efficiency as well as the beam-coupling ratio of the phase gratings recorded in the cells of the nematic liquid crystal hybridized with montmorillonite clay was found to be two to three times higher than that in the pristine nematic cell.

Two-dimensional metallic nanobowl array transferred onto thermoplastic substrates by microwave heating of carbon nanotubes

The unique heating property of microwave irradiation on carbon nanotubes (CNTs) was applied in fabrication of a new architecture of two-dimensional metallic nanobowl array on a thermoplastic substrate. Vertically aligned CNT film was grown on a metal coated polystyrene (PS) submicron sphere array and then transferred onto a polycarbonate (PC) substrate by microwave heating. The back diffracted light spectra of this structure were measured and discrepancies between the spectra and that predicted from a diffraction relationship were studied. It is suggested that the discrepancies were related to the shape and the refractive indices of the materials.

The fabrication of a carbon nanotube array using a catalyst-poisoning layer in the inverse nano-sphere lithography method

A new method for the fabrication of periodic CNT arrays was developed in this study, which involves the use of the inverse nano-sphere lithography (INSL) process. Mo of a honeycomb pattern, acting as a catalyst-poisoning layer, was produced by the nano-sphere lithography (NSL) process; the Mo poisoned the catalyst and prevented CNT growth where deposited, and as a result, a periodic CNT pattern was obtained. Using this method, the uniformity of the CNT array can be improved by preventing the negative effect of arrangement defects in self-assembled monolayers. The size and the period of the CNT array can be adjusted by careful selection of the polystyrene (PS) sphere diameter. X-ray photoelectron spectroscope (XPS) analysis revealed that the Co catalyst was ineffective on the areas of Mo deposition due to the diffusion of Co into the Mo layer.