Sun Hong Choi

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.

Surgical treatment of solid pseudopapillary neoplasms of the pancreas and risk factors for malignancy

The aim of this study was to identify clinical predictors of malignancy and surgical strategies for pancreatic solid pseudopapillary neoplasm (SPN) by analysis of surgical outcomes at a single institution.

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.

Effects of growth parameters on the selective area growth of carbon nanotubes

Abstract Effects of growth parameters such as plasma intensity, flow rate, composition of reactant gases, growth temperature, and hole size on the selective area growth (SAG) of carbon nanotubes (CNTs) were investigated using the triode type field emission array structure in plasma enhanced chemical vapor deposition (PECVD) system . As the plasma intensity was increased, the diameter of CNTs was reduced from 180 to 90 nm, but the growth rate was promoted. With an increase in the NH 3 flow rate, the average diameter of CNTs was decreased due to the enhanced etching effect by NH 3 . An increase in the total flow rate of reactant gases reduced the growth rate of CNTs, but the average diameter of CNTs remained nearly constant. An increase in growth rate and diameter was observed at higher growth temperatures. As the hole size of the triode structure increased, the growth rate of CNTs gradually decreased because of the reduced lateral diffusion of reactant species into the hole.

Randomized multicentre trial comparing external and internal pancreatic stenting during pancreaticoduodenectomy.

There is no consensus on the best method of preventing postoperative pancreatic fistula (POPF) after pancreaticoduodenectomy (PD). This multicentre, parallel group, randomized equivalence trial investigated the effect of two ways of pancreatic stenting after PD on the rate of POPF.

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.

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.