25
To simplify the experimental setup and eliminate the need for a secondary
heating source, a novel method by which to utilize the residual heat of the end of the
furnace in order to evaporate the mixture was designed. By pumping the mixture
using a Masterflex 7523 continuous pump to near the edge of the furnace, the waste
heat from the furnace is sufficient to evaporate the xylene∕ferrocene mixture so that
it can be carried in the gaseous phase through the reaction zone. In order to ensure
even and consistent dispersion of the growth precursors, two gases, also controlled
by MKS MlOO MFCs controlled by a MKS Type 247 Four-Channel Readout were
used: the “evaporator gas” (15 vol% hydrogen, balance argon) is to help the
evaporated xylene∕ferrocene mixture to be evenly dispersed, and the "carrier gas”
(15 vol% hydrogen, balance argon) was used to carry the precursors∕evaporator
gas mixture through the furnace. An image showing the pump and the MFC bank
can be seen in Figure 2.6.
As can be seen in Figure 2.7, the carrier and evaporator gases are directed
through coaxial channels which surround the precursor mixture, all of which are
made Ofstainless steel tubing and measure 1”, 1∕4", ɪ/ɪθ" in-diameter, respectively.
The carrier gas line ends at the flange of the quartz tube, where it will result in an
even flow which downstream will pick up the reaction gases and carry them
towards the reaction zone. The evaporator gas line is supported by the rigidity of
the ɪʌ" tube, where it will carry the gas to the "evaporator”, a custom-fabricated
part which creates an environment where the evaporated catalyst∕carbon source
can disperse with the evaporator gas before being sprayed radially into the quartz