Monday, April 26, 2010

Carbon Nanotube Arrays Manufactured Inexpensively and Quickly with Iron Catalyst on Quartz Boats

Hon Hai Precision Industry Co., Ltd. (Tu-Cheng, Taipei Hsien, TW) and Tsinghua University (Beijing, CN) received U.S. Patent 7,700,048 for a chemical vapor deposition apparatus to quickly and inexpensively manufacture an array of  super-aligned carbon nanotubes using an iron catalyst on a quartz-boat region.

According to inventors Kai-Li Jiang  (Beijing, CN) and Shou-Shan Fan (Beijing, CN), the reaction chamber has a first gas inlet configured for introducing a carbon source gas and a carrier gas into the chamber, a second gas inlet is configured for introducing a hydrogen gas into the chamber, a guiding tube in communication with the second gas inlet, and a gas outlet. The quartz-boat region is configured for accommodating a quartz boat for supporting a substrate; wherein the guiding tube extends inwardly a distance sufficient to enable the majority of the introduced hydrogen gas that reaches the substrate not to react with the carbon source gas.
The quartz boat is disposed in the reaction chamber, the quartz boat has an obliquely oriented portion for accommodating the substrate. The reaction chamber is substantially tubular in shape. The carrier gas includes at least one of the noble gases or nitrogen gas. The carbon source gas is selected from the group consisting of ethylene, methane, acetylene, ethane, and any combination of them.

Compared with conventional CVD devices for making carbon nanotube arrays, the device s has the following advantages. Firstly, the present apparatus can perform at a relatively low temperature, for example, in the range from 600 to 700 degree  C. In the preferred embodiment of the apparatus, an array of bundled and super-aligned carbon nanotubes can be synthesized at temperatures in the range from 620 to 690 degree  C. Secondly, growth speed and yield of carbon nanotubes are both improved. After growing carbon nanotubes for 30 to 60 minutes, the carbon nanotube array has a height of a few hundred micrometers to a few millimeters. Thirdly, the apparatus and method for growing carbon nanotubes is inexpensive. A carrier gas and a carbon source gas of the preferred method can be inexpensive argon and acetylene. A catalyst can be inexpensive iron. 

FIG. 1 is a schematic view of an Tsinghua University and Hon Hai  apparatus for making an array of carbon nanotubes in accordance with a preferred embodiment of theapparatus for CNT production. 
FIG. 2 shows a Scanning Electron Microscope (SEM) image of the array of carbon nanotubes formed by the apparatus of FIG. 1; and
FIG. 3 shows a Transmission Electron Microscope (TEM) image of the array of carbon nanotubes formed by the apparatus of FIG. 1

Referring to FIGS. 2 and 3, a SEM image and a TEM image of the multi-walled carbon nanotube array formed by the present apparatus are shown. It can be seen that the carbon nanotubes in the carbon nanotube array are highly bundled and super-aligned. The height of the carbon nanotube array is about 300 micrometers. 

Density, diameter and length of the multi-walled carbon nanotube array can be controlled by adjusting the flow rates of the carbon source gas and the carrier gas, and by altering the predetermined temperature and the reaction time. In addition, the hydrogen introduced by the second gas inlet can flow to the substrate, and act on the catalyst directly. That is, the hydrogen can avoid reaction with the carbon source gas, and the catalyst can be activated directly by the hydrogen. In this way, the growth speed of the carbon nanotubes is increased and the height of the carbon nanotube array is enhanced. In the preferred first embodiment, the reaction time is in the range from 30 to 60 minutes. The synthesis method can produce carbon nanotubes with a length greater than 3-400 micrometers, and have a diameter in the range from 10 to 30 nanometers

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