Standard Protocols
Advanced Techniques
Under development
General Advice
Inspiration
Standard Protocols
Advanced Techniques
Under development
General Advice
Inspiration
Electron beam evaporation of pure iron is an excellent way to deposit catalyst. If a thin layer is used (0.1 -0.4 nm) then you can grow exclusively single wall CNTs. We use the recipe published by the Rogers group (Nature Nanotech 2007). It is useful to look at the McEuen group's version of this recipe.
A 0.2 nm layer of Fe is invisible when you inspect the chip by naked eye, but you can see the iron in an AFM (image below). The Fe layer will bead up on the surface at high temperature and yield nanotube tube diameters < 2 nm.
Figure: 20×20 micron AFM scan showing CNTs growing from a stripe of evaporated iron (10 microns wide and 0.1 nm “thick”) deposited on ST-cut quartz. Patterning was done by photolithography. Nanotubes can be seen growing above and below the iron stripe. Growth direction is perpendicular to the wafer flat. |
We have tried at least four different iron-based catalysts that are suspended in a solvent. Even more variations exist in the literature. The alumina supported catalyst is tried and true:
Figure: SEM image of CNTs growing from alumina supported catalyst. Scale bar is 200 nm. The advantage of alumina supported catalyst is the high surface area of the alumina. The high surface area leads to more nanotube nucleation sites. One disadvantage is that alumina nanoparticles, together with sticky nanotube grass, stick to the AFM tip during imaging (it is best to avoid imaging directly over the alumina!). A second disadvantage is that the diameter distribution of CNTs tends to be broad. | |
This image comes from Ethan Minot's PhD thesis (Fig. 3.2). The alumina supported catalyst is patterned in a 4 x 4 micron square. Hundreds of CNT grow inside the 4 x 4 square, making it look like a bird's nest. |
The CVD furnace uses quartz tubing to contain the gas flow while everything (chip, catalyst, gas) is heated to high temperature. We have spare quartz tubes in the event that the tube becomes contaminated. The quartz tube can become contaminated with carbon soot due to alcohols that have evaporated and condensed into the gas lines. To avoid this problem, the gas lines must be purged at low temperature prior to the growth process.
*UPDATED 2022 by Dublin
(Click here for other recipes) and old_recipes
Startup/Loading chips
Ethanol/methanol levels: Use around half as much Methanol as Ethanol. (In my experience, a 1:1 ratio produces more multi-tube sites and shorts, so this ratio is important. - Dublin)
Growth Process
Input purge parameters:
Anneal:
Transition:
Growth:
Growth Parameters:
Anneal:
Transition:
Growth:
Updated 04-16-2013 by Heather
The 4“ growth system primarily differs from the 1” system in two ways. First, the larger diameter quartz tube allows for growth on larger substrates (growth on 3“ silicon wafers is possible). Second, the 4” furnace can be operated under vacuum, allowing for the growth of graphene as well as carbon nanotubes. The 4“ CVD furnace uses quartz tubing to contain the gas flow while everything (chip, catalyst, gas) is heated to high temperature.
Before using the system:
When using the system always adhere to the standard operating procedure.
Leak checking is suggested every time the growth tubes are switched. Leaks during growth can result in bad yeilds and low growth, or, in a worst case scenario, an explosion.
The residual gas analyzer (RGA) allows you to monitor the partial pressures of individual gases in the growth chamber.
Gases are ordered from Industrial Gas and Welding Supplies, Corvallis: