Shigeharu Ohkura

Low Temperature Synthesis of Aligned Carbon Nanotubes by Inductively Coupled Plasma Chemical Vapor Deposition Using Pure Methane

Inductively coupled plasma chemical vapor deposition combined with substrate biasing using pure methane was applied to low-temperature synthesis of carbon nanotubes. We found that the resultant carbon nanotubes were crystalline even at a growth temperature of 500°C. The growth mechanism of the crystallized carbon nanotubes was discussed in terms of the moderate etching of carbon deposit by hydrogen species dissociated from methane in inductively coupled plasma.

Improvement in Field Emission Uniformity from Screen-Printed Double-Walled Carbon Nanotube Paste by Grinding

We have improved field emission uniformity in a screen-printed paste composed of double-walled carbon nanotubes (DWNTs), which were ground by planetary ball milling (PBM). Results showed that after grinding pristine DWNTs, carbonaceous particles that affected the roughness of the DWNT paste were atomized and long DWNTs were cut. Ground DWNTs were dispersed uniformly on a stainless steel substrate, thereby improving field-emission uniformity. This simple grinding technique is expected to be applicable to low-cost and high-yield processing that produces a DWNT paste for field emitters.

Synthesis of aligned bamboo-like carbon nanotubes using radio frequency magnetron sputtering

Vertically aligned bamboo-like carbon nanotubes (CNTs) are successfully synthesized on Ni-coated Si (Ni/Si) substrates by hot-filament-assisted radio frequency (rf) magnetron sputtering. Transmission electron microscopy analysis reveals that a bamboo-like structure is formed inside the nanotube that has a catalytic Ni nanoparticle on the tip. It is likely that moderate carbon particle energy plays an essential role in synthesizing CNTs by sputtering. To verify its importance, we conduct a bias-sputtering experiment to test the effect of negative voltages on the energy of the carbon particles. Furthermore, we find that the diameter and density of the aligned bamboo-like CNTs can be controlled by changing the number density of Ni nanoparticles on Si substrates.

RBS/channeling study on the annealing behavior of Cu thin films on Si(100) and (111) substrates

Abstract The thermal annealing behavior of Cu thin films deposited on Si(100) and (111) substrates has been studied by RBS/channeling methods. The effect of substrate pretreatment and of annealing conditions has been investigated. The initial stage of the interface formation has also been studied in ultrahigh-vacuum conditions.

Surface morphology and field emission characteristics of carbon nanofiber films grown by chemical vapor deposition on alloy catalyst

Carbon nanofiber (CNF) films have been successfully grown on Pd-Se, Fe-Ni, and Ni-Cu alloy catalysts at low temperatures by a thermal chemical vapor deposition method. Among these alloy catalysts, Ni-Cu alloy catalyst was found to be most suitable for low temperature growth of CNF (400 °C). Using Pd-Se and Fe-Ni alloy catalysts, CNFs were grown at the lowest temperature of 500 °C. The CNFs grown using Pd-Se catalyst were found to have more defective structure than that obtained with the other catalysts, and exhibited excellent field emission property (threshold field is estimated about 1.1 V/mm). It is likely that defects play a role as electron emission sites.

Method for Aligned Bamboolike Carbon Nanotube Growth Using RF Magnetron Sputtering

We present a method for aligned bamboolike carbon nanotube (CNT) growth using RF magnetron sputtering. It has been revealed that aligned CNTs can be synthesized by adopting a hot filament in the sputtering system, as demonstrated for CNTs on an Ni/Si substrate. The resultant CNTs were found to be aligned vertically on the substrate with uniform height and have a bamboolike structure. Similar results were obtained for sputtering deposition under a negative sample bias, indicating that the effect of the hot filament can be attributed to the energy enhancement of the carbon particles impinging on the growth front, which plays an essential role in the growth of CNTs by sputtering.

Synthesis of Vertically Aligned Carbon Nanofiber Films by RF Magnetron Sputtering

Abstract : The aligned carbon nanofibers were synthesized on Si substrates using RF magnetron sputtering with a hot filament. The hot filament was made of tungsten wire and its temperature was up to 2000 degrees C during the deposition. Nitrogen was used as the sputter gas at a relatively low pressure of 2xlO(exp-2) Torr. The sputtering deposition was carried out at a substrate temperature of 700 degrees C. The nanofibers were grown vertically on the substrates. The diameters and the density of the fibers were about 30-45 nm and 10(exp 9) cm(exp-2), respectively.

Formation of Graphite Layers during Carbon Nanotubes Growth

We have investigated carbon products deposited on large catalyst islands during carbon nanotube growth by thermal chemical vapor deposition on a Fe–Ni catalyst film, using cross-sectional analysis by transmission electron microscopy and scanning electron microscopy. It was found that carbon atoms covering on the surface of Fe–Ni large islands form graphite layers with high crystallinity at a temperature as low as 700°C. The growth mechanism of the graphite layers can be explained in terms of precipitation of diffused carbon atoms from the inside of large catalyst islands.

Large field emission from carbon nanotubes grown on patterned catalyst thin film by thermal chemical vapor deposition

Here, we report the large electron emission from carbon nanotubes grown by thermal chemical vapor deposition method combined with patterning process. It was found that emission property greatly depends on the size and density of patterned catalyst thin films on the substrate. The threshold applied electric field considerably decreased with use of the patterned thin films in comparison with the plain thin film.

INFLUENCE OF THE PLASMA CONDITION ON THE MORPHOLOGY OF VERTICALLY ALIGNED CARBON NANOTUBE FILMS GROWN BY RF PLASMA CHEMICAL VAPOR DEPOSITION

Vertically aligned carbon nanotube (VACNT) films have been grown by RF plasma chemical vapor deposition (RF-PECVD) with a controlling plasma condition. From the in situ optical emission spectroscopy (OES) and self-bias measurements, we have investigated the relationship between the morphology of VACNTs and the plasma condition in PECVD. CH radical and atomic hydrogen peaks were prominent in the OES spectra of CH4 plasma. The plasma condition was changed by varying the interelectrode distance in PECVD. With increasing interelectrode distance, the diameter and density of VACNTs increased as a result of the increase in plasma density, the fraction of CH radicals, and self-bias. It is likely that the fraction of CH radicals in plasma influences promotion of the growth of CNTs, while the self-bias induces their vertical alignment.