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makes it very difficult to grow CNTs on anything other than simple, relatively planar
substrates such as silicon wafers.
2.1.2. Construction of a Water-Assisted A-CNT Growth Furnace
The first step in pre-deposited catalyst CNT synthesis is having a sufficiently
hot reaction zone in order to initiate CNT nucleation. This is typically done through
the use of a tube furnace, where these temperatures can be achieved while assuring
even, laminar flow of the reaction gases over the substrate to limit growth
inconsistencies due to turbulence. Due to the sensitivity of the growth process,
having a consistent temperature profile across the desired growth zone is of
paramount concern. For this reason, long tube furnaces are generally used for
applications where the growth is to occur over a large area, as the longer the
furnace, the more even the temperature in the center region, leading to more
consistent overall growth. For this work, a Thermolyne 79400 tube furnace with a
26" heating zone which can accommodate a 2" in-diameter quartz reaction tube was
used.
The beauty of the pre-deposited catalyst growth method lies in its relative
simplicity. Since the catalyst is already deposited on the substrate prior to
synthesis, all one needs to be concerned with is the environment of the reaction
zone and the flow of each gas used. However, since the kinetics of CNT synthesis are
so complicated and difficult to predict, tight, repeatable control over every aspect of
the reaction is essential. As the substrate for growth, silicon wafers pre-deposited
with the catalyst were used as described in Figure 2.1. 1.5 nm of iron was