Chwung-Shan Kou

Field emission from a composite structure consisting of vertically aligned single-walled carbon nanotubes and carbon nanocones

Vertically aligned single-walled carbon nanotubes (VA-SWCNTs) have been fabricated on carbon nanocones (CNCs) in a gravity-assisted chemical vapour deposition (CVD) process. The CNCs with nanoscale Co particles at the top were first grown on the Co/Si(100) substrate biased at 350?V in a plasma enhanced chemical vapour deposition process. The CNCs typically are ~200?nm in height, and their diameters are ~100?nm near the bottom and ~10?nm at the top. The nanoscale Co particles ~10?nm in diameter act as catalysts which favour the growth of VA-SWCNTs out of CNCs at 850??C in the gravity-assisted CVD process. The average length and the growth time of VA-SWCNTs are ~150?nm and 1.5?min, equivalent to a growth rate of ~6??m?h?1. The diameters of VA-SWCNTs are estimated to be 1.2?2.1?nm. When VA-SWCNTs are fabricated on CNCs, the turn-on voltage is reduced from 3.9 to 0.7?V??m?1 and the emission current density at the electric field of 5?V??m?1 is enhanced by a factor of more than 200. The composite VA-SWCNT/CNC structure is potentially an excellent field emitter. The emission stability of the VA-SWCNT/CNC field emitter is discussed.

Field emission from diamond nanotips treated with nitrogen plasma immersion ion implantation

Diamond nanotips were synthesized on diamond/Si substrates by using a microwave plasma-enhanced chemical vapor deposition process. The diamond nanotips are ~1??m in height and the diameter at the bottom of a nanotip is ~200?nm. The as-grown diamond nanotips exhibit excellent field emission characteristics after treating with nitrogen plasma immersion ion implantation (PIII) for 10?min. A low turn-on field of 3?V??m?1 and a high current density of 4?mA?cm?2 at 9?V??m?1 are achieved. The morphologies of diamond nanotips are unchanged after the nitrogen PIII treatment. The diamond quality reduces with treatment time. The sp3 bonds in diamond can be broken by the nitrogen ions accelerated by the pulse voltage of ?25?kV, which results in G peak broadening in Raman spectra. Several nanoscale amorphous regions are generated in a crystalline diamond nanotip, observed by the high resolution transmission electron microscope. The improvement of field emission properties is correlated to the amorphous regions and possible implantation-induced atomic defects.

Mechanism in determining pretilt angle of liquid crystals aligned on fluorinated copolymer films

This work explores the surface treatment of copolymer materials with fluorinated carbonyl groups in various mole fractions by ultraviolet irradiation and ion-beam (IB) bombardment and its effect on liquid crystal (LC) surface alignments. X-ray photoemission spectroscopic analysis confirms that the content of the grafted CF2 side chains dominates the pretilt angle. A significant increase in oxygen content is responsible for the increase in the polar surface energy during IB treatment. Finally, the polar component of the surface energy dominates the pretilt angle of the LCs. (Some figures in this article are in colour only in the electronic version)

Passivation effect on the liquid crystal alignment on a-C:H films: A two-step treatment by argon and hydrogen plasma beam scanning

A two-step treatment by argon (Ar) and hydrogen plasma beam scanning was developed to modify the surface bonds of a hydrogenated amorphous carbon (a-C:H) film on indium tin oxide glass. The modified a-C:H film is an excellent layer for liquid crystal alignment, on which the pretilt angle of a nematic liquid crystal (ZLI-2293) can be adjusted by the two-step scanning treatment. The chemical bonding characteristics of the as-scanned a-C:H films were measured using micro-Raman and x-ray photoemission spectroscopies. The antiparallel cells were filled with the nematic liquid crystal on the as-scanned a-C:H film to measure the pretilt angle. Experimental results indicate that the carbon dangling bonds are generated through a bond-breaking process during the Ar plasma beam scanning step (first step). The hydrogen plasma beam scanning step (second step) can passivate some of the carbon dangling bonds that are generated in the first step. The pretilt angle decreases as the hydrogen plasma beam scanning time incre...

Field Emission from a Carbon Nanofiber/Carbon Nanocone Composite Structure Fabricated by a Two-Step Growth Process

A composite structure of carbon nanofiber (CNF) and carbon nanocone (CNC) has been successfully fabricated on the Co/Al/Si(100) substrates by using microwave plasma-enhanced chemical vapor deposition. A hydrogen pretreatment is required to form Co-Al nanoparticles on the substrate at 450°C, which is essential for the subsequent CNF/CNC growth. The CNF/CNC composite structure is fabricated by a two-step process in which bundles of CNFs are formed on the as-pretreated substrate at 450°C and a CNC structure is subsequently formed at 650°C by a coalescence mechanism. Raman spectra indicate that sp 2 bonds in C=C chains play a role in connecting CNFs in each bundle during the formation of CNCs. An upward growth of CNFs on the top of CNCs occurs during coalescing CNFs. The CNF/CNC composite structure exhibits very good field emission characteristics, better than CNFs. The optimum turn-on field for the CNF/CNC structure is 2.5 V/μm, which is defined as the electric field at a current density of 10 μA/cm 2 . The current density is 4.5 mA/cm 2 at 6 V/μm.

Field Emission from Hydrogenated Amorphous Carbon Nanotips Grown on Cu ∕ Ti ∕ Si ( 100 )

Hydrogenated amorphous carbon (a-C:H) nanotips have been successfully grown on Cu/Ti/Si(100) by microwave plasma-enhanced chemical vapor deposition. A Cu etching process occurs simultaneously during the growth of the a-C:H nanotips. Both the Cu etching and a-C:H nanotips growth rates continuously increase with time. In the beginning, the Cu etching rate is approximately 3 nm/min and the upward growth rate of the a-C:H nanotips is approximately 1.2 nm/min. At the end of the growth, the Cu etching rate reaches 9 nm/min and the upward growth rate of the a-C:H nanotips reaches 5 nm/min. An etching-growth mechanism has been proposed to explain the formation of a-C:H nanotips on Cu/Ti/Si( 100). The structure of the a-C:H nanotips exhibits very good field-emission characteristics where a low turn-on field of 3.2 V/μm at 10 μA/cm 2 is achieved.

Characteristics of heating mode transitions in a radio-frequency inductively coupled plasma

In this report, plasma heating mode transitions at different pressures in an inductively coupled plasma source are investigated. Results show that the plasma properties abruptly change as the mode transition occurs at pressures where the electron–neutral particle collision frequency is higher than the wave frequency while they slowly vary at the low-pressure side. Additionally, the electron energy distribution function changes from a Druyvesten to a Maxwellian distribution in mode transitions at high pressure.

Field Emission from One-Dimensional Submicron Diamond Rods

One-dimensional boron-doped submicron diamond rods (SDRs) were fabricated on diamond/Si substrates by oxygen plasma etching. The SDRs are 4.5 mm in height and 383 nm in diameter. Iron oxide coated on SDRs is essential in the formation of onedimensional SDRs. However, the as-etched SDRs suffer with high turn-on field (ETO) and low field emission current density (JFE) due to the iron oxide. A huge improvement in the field emission characteristics can be achieved by removing iron oxide using a wet-etch process in a diluted HCl (37%). After the wet-etch, the SDRs exhibit a low ETO value of4.5 V/mm (at 10 mA/cm ) and a high JFE value of 30 mA/cm 2 (at 8.5 V/mm). The FE emitter is only stable for a short period of time at high current stress owing to the rounding of the tips of SDRs. VC 2011 The Electrochemical Society. [DOI: 10.1149/1.3592207] All rights reserved.

Schottky diode fabricated on a single crystalline diamond rod

The fabrication process of Al/diamond Schottky diodes on single crystalline diamond rods (SCDRs) was demonstrated. SCDRs of submicron diameters were obtained by etching a polished polycrystalline diamond film in oxygen plasma. The as-scratched SCDR was confirmed to be single crystalline diamond by electron diffraction measurements showing the same fuzzy spot pattern at different parts of an SCDR. Each SCDR was extracted from a grain in the polycrystalline film where the grain size served as a limit of the length of an SCDR. Al/Ti and Al metals were deposited to form ohmic and Schottky contacts, respectively. A hydrogen plasma treatment is an essential step prior to the formation of an Al/diamond Schottky contact in order to improve the device performance. The submicron scale Al/diamond Schottky diode exhibits a very high current density of 1.4 × 10(4) A cm(-2) at a forward bias (V(F)) voltage of - 3 V.

Liquid Crystal Alignment on Plasma Beam Scanned Alkylsiloxane Self-Assembled Monolayers

The octadecyl-trimethoxysiloxane self-assembled monolayers (SAMs) exhibit better uniformity and smoothness on hydrogenated amorphous carbon (a-C:H) films than on indium tin oxide glasses. The liquid crystal alignment on the SAM/a-C:H can be greatly improved by Ar plasma beam scanning. The pretilt angle increases abruptly with Ar plasma beam scanning time within 5 s and reaches a maximum value of about 5° at a longer scanning time. The surface roughness of SAM slightly increases from 0.10 to 0.13 nm after Ar plasma beam scanning. This implies that bond breaking occurs on the SAM surface during the plasma beam scanning. Fourier transform infrared spectrometer and X-ray photoemission spectroscope data indicate that plasma beam scanning can sputter off the CH 2 bonds in the alkyl chain of SAM. The amount of oxygen on the SAM surface increases after plasma beam scanning and the increase of oxygen is attributed to the formation of C-O bonds during air exposure after plasma beam scanning.