Patterned Growth of Carbon Nanotubes or Nanofibers
- Wednesday, 18 April 2007
Numerous parameters of deposition conditions, structures, and compositions affect what is grown.
A method and apparatus for the growth of carbon nanotubes or nanofibers in a desired pattern has been invented. The essence of the method is to grow the nanotubes or nanofibers by chemical vapor deposition (CVD) onto a patterned catalyst supported by a substrate.
A typical first-sublayer metal is Pt, Pd, Cr, Mo, Ti, W, or an alloy of two or more of these elements. A typical metal for the second sublayer or for an undivided first layer is Al at a thickness ≥1 nm or Ir at a thickness ≥5 nm. Proper choice of the metal for a second sublayer of a first layer makes it possible to use a catalyst that is chemically incompatible with the substrate.
In the next step, a mask having holes in the desired pattern is placed over the coated substrate. The catalyst is then deposited on the coated substrate by ion-beam sputtering through the mask. Optionally, the catalyst could be deposited by a technique other than sputtering and/or patterned by use of photolithography, electron- beam lithography, or another suitable technique. The catalytic metal can be Fe, Co, Ni, or an alloy of two or more of these elements, deposited to a typical thickness in the range from 0.1 to 20 nm.
Following deposition of the patterned catalyst, a shutter is moved into place to protect the sputtering equipment against CVD of carbon, then a hydrocarbon feed gas (primarily CH4, C2H2, or C2H4 ) heated to a suitable temperature is admitted into the chamber. Optionally, the feed gas can be part of a mixture that includes an inert carrier gas. The heated feed gas decomposes into hydrogen and carbon, with deposition of the carbon on the catalyst. Whether what are grown are single-walled nanotubes (SWNTs), multi-walled nanotubes (MWNTs), or nanofibers depends primarily on the feed gas and temperature used in CVD and secondarily on the structures and compositions of the first layer and the patterned catalytic second layer. For example, for growing SWNTs, the preferred gas is CH4 and the preferred temperature is ≈900 °C. For growing MWNTs, the preferred gas is C2H2 or C2H4, the preferred temperature is ≈750 °C. For growing nanofibers, it is preferable to form a plasma discharge in the chamber and to maintain the temperature between 400 and 700 °C.
This work was done by Lance D. Delzeit of Ames Research Center.
Inquiries concerning rights for the commercial use of this invention should be addressed to the Patent Counsel, Ames Research Center, (650) 604-5104. Refer to ARC-14613.