Fabrication of diamond via pulsed direct-current plasma
assisted chemical vapour deposition
Catrin Harris*
* Department of Chemistry, University of Bristol, United Kingdom
A new, university built pulsed direct-current plasma assisted chemical vapour deposition
reactor(PDC PA-CVD) has been used to deposit thin diamond films onto molybdenum plates.
Due to the high thermal conductivity of diamond this has potential uses in high powered
microwave electronic devices. During this project improvements have been made to the
reactor and conditions optimised to create diamond which fulfils these electrical applications.
Apparatus and conditions for growth
The PDC PA-CVD reactor is computer controlled
via a Delphi programme. With the chamber under
low vacuum (2 mT) a hydrogen plasma is struck
between two parallel plates. The pressure is
gradually increased, then methane is added (4%
by volume in hydrogen) to produce diamond from
its carbon radicals. A range of parameters were
studied to find the optimum conditions for diamond
growth within the reactor. These included, but are
not limited to;
● Plate temperature – 800 °C
● Plate separation – 2cm
● Power/Voltage – 650 W
● Pulse period – 3 μs
● Chamber pressure – 80 T
These were varied either by
computer controls or changes
to plate thickness and separation.
Figure 1 – PDC PA-CVD reaction chamber
Diamond as a solar heated source
Figure 3 - Raman data from diamond sample
grown in PDC PA-CVD reactor. Peak at 1332 cm-1
is characteristic of diamond.
PDC PA-CVD reactor development and
improvements
●Power feed through – Due to the initial design of
the reactor, a short circuit occurred at the power
inlet, causing the plasma to arc. An improved
replacement was designed.
●Pressure management – The pressure of the
The thermal conductivity of diamond is higher than
all other solids at room temperature. Impurities
lower the thermal conductivity, hence the
importance of growing isotropic diamond via
chemical vapour deposition. Isotropic diamond is
expected to have thermal conductivity an order of
magnitude greater than natural 1.1% carbon-13
doped diamond. We built a solar tracker which
locates the sun based on GPS coordinates. In the
future diamond solar devices may be mounted in
order to capture the suns energy.
chamber needed to be delicately controlled via a
butterfly valve. To improve control, the pressure
transducer was bypassed, with electrical
connections directly to the computer.
Evidence of diamond growth
gas inlet was designed to deliver gas more directly
to the sample, improving growth efficiency.
Figure 2 - SEM
showing large facets
of diamond crystals
grown in PDC PACVD reactor.
●Plate support – The molybdenum clips
supporting the top plate failed under the intense
heat of the plasma (approx 1300°C). A
replacement needed to be designed and fitted to
support the weight of the structure.
●Gas inlet – In order to improve gas flow, a new
●Electric field – Through varying reactor
conditions and literary sources, it was found the
value of the electric field affected diamond growth,
an important development for future success.
Supported by the University Research Strategy Fund