Lujun Pan

Growth mechanism of carbon nanocoils

Carbon nanocoils were prepared by catalytic pyrolysis of acetylene using iron-coated indium tin oxide as the catalyst. The effects of the constitution of catalyst, the growth temperature and time, the flow rate of acetylene gas on the growth of carbon nanocoils were investigated. It is found that the coils grow mainly from the interface of iron and indium tin oxide films. The coils generally consist of two or more nanotubes. Each coil has its own external diameter and pitch, which is determined by the structure of the catalyst at its tip. The growth of the carbon nanocoil is considered to be due to the nonuniformity of the carbon extrusion speed at different parts of the catalyst particle containing iron, tin, indium and/or oxygen. It is confirmed that iron is crucial in the formation of a nanotubule and indium tin oxide induces the helical growth of the nanotubule.

Synthesis of Carbon Tubule Nanocoils in High Yield Using Iron-Coated Indium Tin Oxide as Catalyst

We have synthesized carbon coils of nanometer-scale size by catalytic thermal chemical vapor deposition. The catalyst used is iron-coated indium tin oxide and the carbon source is acetylene. The yield of carbon coils is over 95% at a growth temperature of 700°C. The carbon coil usually consists of two or more carbon tubules and each of them grows with its own diameter and pitch. The external diameters of the coils are from several tens to several hundreds of nanometers. It is found that iron plays an important role in the growth of carbon nanotubes, while indium, tin, oxygen, and/or their alloys are necessary in the formation of the coils.

Field Emission Properties of Carbon Tubule Nanocoils

The first carbon nanocoil field emitter has been prepared by catalytic thermal chemical vapor deposition and its properties of field emission have been investigated. The carbon nanocoils grow selectively from the patterned iron film and maintain their self-organization well. The field emission measurement shows that the turn-on field is as low as 180 V at a 130 µm gap. High emission current density, excellent stability, especially uniformity of the field emission from carbon nanocoils have been observed. These properties suggest that the carbon nanocoils is an attractive candidate for the fabrication of flat panel field emission display.

Growth of Super Long Aligned Brush-Like Carbon Nanotubes

Efficient chemical vapor deposition (CVD) synthesis of super long (7 mm) aligned carbon nanotubes (CNTs) with highdensity is reported here. Activity of catalyst nanoparticles has been achieved for very long time periods (ca. 12 h) by optimization of experimental parameters. The relative levels of ethylene and water, as well as those of ethylene and H2, were found to be most important for achieving extended-time activity of the catalyst. Transmission electron microscope (TEM) images revealed that the nanotubes were mainly double-walled, but very few single-walled and multi-walled nanotubes were also present in the sample. [DOI: 10.1143/JJAP.45.L720]

In Situ Study of Iron Catalysts for Carbon Nanotube Growth Using X-Ray Diffraction Analysis

We have investigated how an iron catalyst changes during the growth of vertically aligned carbon nanotubes by in situ measurement of X-ray diffraction. It is found that heating the catalyst film to a growth temperature of 700°C in He atmosphere induces its oxidation beyond 100°C due to adsorbed moisture and changes the film to particles at approximately 600°C. At 700°C, the catalyst particles consist mainly of iron oxide with a cubic system. By feeding C2H2, the catalyst starts to be deoxidized and then absorbs carbon atoms to form Fe-C and Fe3C. The growth mechanism of nanotubes is discussed in terms of the crystalline phase and orientation of the catalyst.

Synthesis of Multiwalled Carbon Nanocoils Using Codeposited Thin Film of Fe–Sn as Catalyst

Multiwalled carbon nanocoils (CNCs) have been synthesized by a method of thermal chemical vapor deposition (CVD) using a codeposited thin film consisting of Fe and Sn as catalysts. It has been found that the multiwalled CNCs are thinner and have a higher crystallinity than conventional CNCs. The catalyst particles are observed at the roots of CNCs, with diameters much larger than the line diameters of the coils. These large particles are formed by the aggregation of Sn and Fe reduced by the C2H2 gas in CVD. These results indicate that Sn plays a crucial role in the growth of the multiwalled CNCs, and a base growth mechanism that differs from conventional growth mechanisms has been experimentally observed and analyzed.

Field Emission Properties and Structural Changes of a Stand-Alone Carbon Nanocoil

Field emission from a stand-alone carbon nanocoil has been investigated using a field-emission microscope. It was found that the emission spot consists of two parts: one is from the tip of the nanocoil and the other is from the side body of the top surface, which proves that the emission from a carbon nanocoil occurs not only at its tip, but also on its top surface where the electric field is concentrated. It was also confirmed that the structure of the carbon nanocoil changes during the field emission, which is considered to be induced by the Joule heating of the large emission current.

Effect of Morphology on Field Emission Properties of Carbon Nanocoils and Carbon Nanotubes

Helical carbon nanocoils exhibit excellent field emission properties, and are thus expected to be applicable as electron emitters in field emission displays. We have synthesized carbon nanocoils with different diameters by the catalytic thermal decomposition of acetylene using iron–indium–tin–oxide catalysts. It is found that the turn-on voltage is decreased by decreasing the average diameter of the grown carbon nanocoils. The turn-on voltage of as low as 30 V at the electrode gap of 130 µm was achieved when the coil diameter is decreased to 60 nm. The calculation for the concentration of the electric field on the coil surface has been performed using a finite element method. It is found that the strength of the electric field around the top ring of a coil is increased with the decrease of the tubular diameter of the coil and has a similar value as that at the tip of a carbon nanotube, suggesting that the efficiency of the field emission from nanocoils would be higher than that from nanotubes. These results can explain the high stability of field emission from carbon nanocoils.

Effects of iron and indium tin oxide on the growth of carbon tubule nanocoils

Carbon tubule nanocoils have been synthesized at high yield by catalytic thermal decomposition of acetylene gas using iron and indium tin oxide (ITO) as the catalysts. The effect of Fe and ITO on the growth of carbon nanocoils has been investigated. By increasing the content ratio of Sn in the ITO film, the yield of carbon nanotubules may be increased but that of nanocoils is decreased. It is found that Fe-additions lead to the growth of carbon nanotubules, while ITO induces their helical growth. The yield of carbon nanocoils is determined by the elemental ratio of Sn and In.

Diameter Control of Carbon Nanocoils by the Catalyst of Organic Metals

Carbon nanocoils with controlled diameters have been synthesized by thermal chemical vapor deposition using carboxylic acid metals as a precursor of the catalyst. It has been found that the line diameter of the nanocoils is determined by the size of the catalyst particles which can be controlled by adjusting the concentration of carboxylic acid metals in the solution. It is confirmed that the coil diameter of the nanocoils is proportional to the size of the catalyst particles. This is consistent with a proposed hodograph of carbon extrusion from a catalyst particle.