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2.1. Pre-Deposited Catalyst CVD
2.1.1. Introduction to Pre-Deposited CVD Growth
The earliest method of A-CNT production involved the use of a substrate pre-
deposited with the catalyst particles used for CNT synthesis [17]. The deposition of
the catalyst can be accomplished by a few techniques, including sputter coating and
electron-beam evaporation.
The technique of pre-depositing the catalyst prior to growth has a few gains
over trying to deliver the catalyst in the vapor phase; when the catalyst is deposited
on the surface prior to synthesis, the resultant CNTs generally have a much
narrower distribution of sizes. The thickness of this catalyst layer (generally
between .5 and 5 nm thick) will largely will define the diameter of the resultant
CNTs, giving some control over the types of CNTs synthesized [22]. Also, as the
amount of catalyst is tightly controlled, there are fewer growth parameters to
optimize, typically providing more consistent, repeatable growth. Another success
of this technique lies in the complex growth surfaces which can be engineered.
Custom masks can be used to selectively determine where the catalyst will be
deposited, and CNT growth normal to these surfaces can be used to grown 2D
patterns such as towers [36].
Despite these strengths, the main shortcoming of this method lies in the
preparation that needs to be done to the substrate in order to grow CNTs. The
success of the growth is dependent on the application of the catalyst particles, which