Taewon Jung

Enhanced electron emission from carbon nanotubes through density control using in situ plasma treatment of catalyst metal

We controlled the density of carbon nanotubes (CNTs) through in situ NH3 plasma pretreatment and investigated field emission properties with the density variation. Ni catalytic layer was transformed into small nanoparticles with NH3 plasma pretreatment time and power. As NH3 plasma pretreatment time was increased, the growth rate of grown CNTs was gradually decreased. Also, the density of CNTs reduced from 2×109 to 8×106/cm2 with an increase in NH3 plasma pretreatment time from 10 to 30 min for the Ni layer of 10 A. With a decrease in the density of CNTs, the emission current density was increased and turn on electric field was decreased. We obtained large and uniform emission current (about 9 mA/emission area of 0.49 cm2) from CNTs film with the density of 8×106/cm2.

Density control of carbon nanotubes using NH3 plasma treatment of Ni catalyst layer

Abstract The effect of NH 3 plasma pre-treatment on the growth characteristics of CNTs was investigated. We observed that NH 3 plasma pre-treatment etched and conglomerated Ni catalyst film, resulting in the formation of Ni nanoparticles. The aligned CNTs from the Ni nanoparticles were grown by plasma enhanced chemical vapor deposition (PECVD). As Ni film thickness decreased from 300 to 30 A, the size of Ni nanoparticles decreased about from 140 to 90 nm and the average diameter of CNTs became smaller. As the NH 3 plasma power was increased, the density of Ni nanoparticles was decreased, leading to the decrease in the density of CNTs.

Effects of source gases on the growth of carbon nanotubes

Abstract We carry out the in situ analysis of chemical species for the growth of carbon nanotubes (CNTs) in direct current plasma enhanced chemical vapor deposition (DC-PECVD) with C 2 H 2 –NH 3 , C 3 H 4 –NH 3 and CO–NH 3 mixtures by optical emission spectroscopy (OES). From OES analysis, it was shown that the hydrogen related radical was regarded as etching species in CNTs growth and the C 2 and CH radical as available carbon sources for the growth of CNTs irrespective of carbon source gas. As the NH 3 flow rate changed, different chemical species in plasma made effects on the growth of CNTs depending on the source gas.

Growth characteristics of carbon nanotubes using platinum catalyst by plasma enhanced chemical vapor deposition

Abstract In growth of carbon nanotubes (CNTs) using Pt catalyst by plasma enhanced chemical vapor deposition, effects of experimental parameters, such as NH3 plasma pre-treatment, NH3/C2H2 ratio and growth temperature, on the growth characteristics of CNTs were studied in details. It is noteworthy that fine dispersion of numerous nano-sized Pt particles was supported on the wall of a CNT without agglomeration. Application of CNTs with nano-sized Pt particles to the electrodes of the fuel cell can be possible.

Comparison of source gases and catalyst metals for growth of carbon nanotube

Abstract Effects of different carbon source gases and catalyst metals on the growth characteristics and emission properties of carbon nanotubes (CNTs) were investigated. As the flow rate ratio of NH3/C3H4 increased, the growth rate of CNTs was enhanced and the average diameter of CNTs became smaller. Ni was more efficient for the field emission of CNTs than any other catalyst metals when using the C2H2 gas, and in case of C3H4 as the carbon source, Co played an important role as a catalyst. When using the CO gas, Fe was the most activated catalyst for the CNTs growth under the flow rate ratio of CO/NH3 of 18. CNTs grown using different catalyst metals had their corresponding catalyst particles at the top of the tips.

Control of carbon nanotubes density through Ni nanoparticle formation using thermal and NH3 plasma treatment

Abstract We controlled the size and distribution of catalytic Ni nanoparticles to control the density and diameter of carbon nanotubes (CNTs). With an increase in plasma power from 30 to 90 W for Ni layer of 30 A, the average diameter of particles decreased from 157 to 58 nm due to an enhanced etching effect. Size and distribution of Ni nanoparticles varied by plasma power, pre-treatment time and thickness of catalytic layer, resulting in the change in the density of grown CNTs. Density of CNTs reduced from 1×10 9 to 8×10 6 cm −2 , depending on the pre-treatment condition.

High field-emission current of carbon nanotubes grown on TiN-coated Ta substrate for electron emitters in a microwave power amplifier

For field emitters as an electron source of traveling wave tube microwave power amplifiers, field-emission properties of multiwalled carbon nanotubes (MWNTs) grown in situ onto an electrically conducting substrate were systematically characterized. MWNTs grown on a TiN-coated Ta substrate with NH3 plasma pre-treatment exhibited the best field-emission property. The maximum current density and corresponding total emission current were 9.4 mA/cm2 and ∼5 mA at 18.8 V/μm, respectively. These enhanced field-emission properties are caused by the highly conducting buffer layer (TiN), the optimum metal substrate (Ta) that produces high field-emission current, and the control of site density of MWNTs by NH3 plasma pre-etching. Details on the correlation between the field-emission properties and the morphological parameters will be discussed.

Field emission and growth characteristics of carbon nanotubes with optical emission spectroscopy analysis in C3H4 and CO deposition systems

Chemical species during growth of carbon nanotubes (CNTs) in direct current-plasma-enhanced chemical vapor deposition were studied in detail using C3H4–NH3 and CO–NH3 mixtures through optical emission spectroscopy. In the C3H4–NH3 system, the relative intensities of CN (388.3 nm) and CH (431.4 nm) decreased and that of C2 (436 nm) increased, leading to sp2 graphization into the CNT structure, leading to improvement of field emission property of CNTs. In the CO–NH3 system, the trend is completely reversed. Attributed to the balance of kinetics involved, CNTs could be grown most effectively under specific conditions. Based on these results, we suggest the growth mechanism and the correlation between morphologies and field emission properties of CNTs in our system.

Emission properties of carbon nanotubes grown on various catalytic layers coated glass using plasma-enhanced chemical-vapor deposition with CO gas

Using plasma-enhanced chemical-vapor deposition with a gas mixture of CO and NH3, carbon nanotubes (CNTs) were vertically grown on a glass substrate with various catalyst metals and buffer layers. The effects of catalyst metals and buffer layers on the growth and emission characteristics of CNTs have been investigated. The difference in the field-emission characteristics between CNTs with various catalyst metals and buffer layers was mainly attributed to the crystallinity of CNTs, i.e., sp2-binding states of CNTs. These states could be the most effective electron-emission sites.

The commercial huddles of carbon nanotube devices

It has been passed over a decade since the first 5-inch diagonal carbon nanotube (CNT) field emission display was demonstrated. The most of technical issues were solved and the device showed promising performances at that time. However, it is not shown on a market as a new display device although alternative devices like OLED and PDP are on sale. Now scientists and engineers are developing new CNT based devices as like rf amplifiers, THz sources, array e-beam lithography tools, and X-ray sources. The hidden obstacles for the commercialization of CNT devices like the lack of standardization of detailed properties and inspection limitations of process steps should be carefully considered to avoid another failure. The presentation will cover unaddressed but critical huddles for CNT devices commercialization.