J.B. Yoo

The control of neural cell-to-cell interactions through non-contact electrical field stimulation using graphene electrodes

Electric field stimulation has become one of the most promising therapies for a variety of neurological diseases. However, the safety and effectiveness of the stimulator are critical in determining the outcome. Because there are few safe and effective in vivo and/or in vitro stimulator devices, we demonstrate a method that allows for non-contact electric field stimulation with a specific strength that is able to control cell-to-cell interaction in vitro. Graphene, a form of graphite, and polyethylene terephthalate (PET) was used to create a non-cytotoxic in vitro graphene/PET film stimulator. A transient non-contact electric field was produced by charge-balanced biphasic stimuli through the graphene/PET film electrodes and applied to cultured neural cells. We found that weak electric field stimulation (pulse duration of 10 s) as low as 4.5 mV/mm for 32 min was particularly effective in shaping cell-to-cell interaction. Under weak electric field stimulation, we observed a significant increase in the number of cells forming new cell-to-cell couplings and in the number of cells strengthening existing cell-to-cell couplings. The underlying mechanism of the altered cellular interactions may be related to an altered regulation of the endogenous cytoskeletal proteins fibronectin, actin, and vinculin. In conclusion, this technique may open a new therapeutic approach for augmenting cell-to-cell coupling in cell transplantation therapy in the central nervous system.

Development of triode-type carbon nanotube field-emitter arrays with suppression of diode emission by forming electroplated Ni wall structure

Triode-type field-emitter arrays were developed by screen printing a photosensitive paste including single-walled carbon nanotubes. Ni wall structure (NWS) was electroplated to form a thick gate to suppress diode emission induced by strong electric strengths due to an anode potential and to focus electron beams to their destined color subpixels. It was observed in computer simulations, as well in experiments that the NWS with the optimum thickness was effective in reducing the diode emission and enhancing electron-beam focusing by modifying electrical potentials around the carbon nanotube emitters. Our fully sealed field-emission display panel using the field-emitter arrays with the NWS demonstrated full color moving images without serious diode emission and with satisfactory color separation.

Growth interruption studies on vertically aligned 2-3 wall carbon nanotubes by water assisted chemical vapor deposition

Highly aligned, 2-3 wall carbon nanotube (CNT) arrays were used to examine the kinetics of CNT growth. A growth interruption method was used to determine the in situ growth rate. The growth interruption method with a water vapor treatment or acetylene treatment during the interruption enabled the production of CNT stacks with different morphologies. The catalytic activity was also monitored using this method. The lifetime of the catalyst was predicted and verified using the catalyst decay model. High temperature metal oxidation behavior using parabolic curve fitting is assigned to the decay process. Details of the analysis are presented.

Enhanced field emission properties of thin-multiwalled carbon nanotubes: Role of SiOx coating

We report the fabrication, characterization, and field emission properties of (silicon oxide) SiOx coated thin-multiwalled carbon nanotubes (t-MWNTs). The coated t-MWNTs show improved field emission behavior. Initially, raw t-MWNTs (diameter ∼5–8nm) were functionalized by acid treatment. Using spin on glass as a Si precursor, SiOx was coated on the nanotubes by routine chemical methods. The coated samples were characterized by high resolution transmission electron microscopy (HRTEM), Fourier transform infrared (FTIR) spectroscopy, and thermogravimetric analysis (TGA) techniques. The HRTEM results show that the local thickness of the coating varies from ∼1to2nm. The FTIR investigations show the formation of nanophases, such as Si–C, Si–O–C, and intercalated Si–O, at the coating/nanotube interface. The TGA reveals that the coating prevents the high-temperature oxidation and degradation of the nanotubes. The field emission characteristics of the coated, functionalized, and raw nanotubes show that the turn-on...

Electron emission from carbon nanotube-dispersed MgO layer

A simple secondary-electron-emission (SEE)-based source was fabricated using a carbon-nanotube-dispersed MgO precursor solution. This emission source exhibits a high SEE gain as over 103. In addition, the self-sustaining current was observed even after turning off the primary electron beam, then the emission current could be modulated by a small electric field variation (1.2–2V∕μm). The electron energy spectrum of the self-sustaining emission indicates that the major character of the emission is attributed to the field-enhanced SEE rather than direct field emission.

Effect of MgO film thickness on secondary electron emission from MgO-coated carbon nanotubes

In order to understand the enormous high yield of secondary electron emission (SEE) of MgO-coated CNT system, we have investigated the SEE yield (SEEY, δ) and energy spectrum of secondary electron by varying the thickness of an MgO layer. We found that the maximum SEEY is strongly dependent on the MgO thickness, and the large potential drop within the MgO layer contributes to large SEEY.

Field emission properties of modified carbon nanotubes grown on Fe-coated glass using PECVD with carbon monoxide

Abstract Field emission characteristics of carbon nanotubes (CNTs) grown on Fe-coated glass using mixed gases of CO and NH 3 were investigated by varying the growth time and growth condition including in situ re-etching and/or re-growth of CNTs. An increase in growth time resulted in a reduction of a turn-on electric field. However, additional in situ re-etching and re-growth of CNTs after the initial growth yielded a decrease in the emission current from CNTs with a similar turn-on field to as-grown CNTs.

Current increase of MWNT upon the adsorption of dodecanethiol

Organic molecules, here dodecanol and dodecanethiol, were adsorbed on a single multi-walled carbon nanotube (MWNT) to investigate the effect of adsorbates on the electron transport within a MWNT. I–V curve remained unchanged for the adsorption of dodecanol, while the current increased from 2.4mA (before adsorption) to 6.5mA with increasing vapor pressure of dodecanethiol up to 3.2 mbar. Possible explanations for the results above are given in this paper. r 2002 Elsevier Science B.V. All rights reserved.

Field emission properties of plasma treated multiwalled carbon nanotube cathode layers

Improved field emission stability and lifetime have been observed for multiwalled carbon nanotube (MWCNT)-paste cathode layers, after plasma conditioning. Initially, MWCNT paste was synthesized and screen printed on an indium tin oxide coated glass substrate to obtain the cathode layers. These cathode layers were exposed to the Xe∕Ne plasma for a period of ∼1 or ∼3min under different biasing conditions (∼250 and ∼300V). The scanning electron microscopy micrographs, recorded for the untreated (virgin) and plasma treated cathode layers, showed significant variations in their morphology. The field emission analysis showed that the onset macroscopic field was increased from its virgin value of ∼4.65to∼9.05±0.05V∕μm for the plasma treated samples, with a subsequent decrease in the mean field-enhancement factor γav from 1251±13 to 779±43, computed from the Fowler-Nordheim plot. The variations in the current density was measured as a function of time, under low (∼10−6Torr) as well as high (∼10−8Torr) vacuum cond...

Field emission characteristics of self-assembled carbon nanotubes on the gold surface

A new method of fabricating carbon nanotube (CNT) field emitters was approached through self-assembly of thiol-modified CNTs onto gold surface. Deposition of CNTs was accomplished by simple immersion of the gold substrate into the thiol-modified CNT solution overnight. The CNTs are deposited as random aggregates of CNT bundles. The I-V measurement of the self-assembled CNTs shows a relatively good field emission characteristics with a low turn-on field (2.5 V//spl mu/m) and a high current density (40 /spl mu/A/cm/sup 2/ at 3 V//spl mu/m).