Growth of Graphene and MoS2 by Chemical
Vapour Deposition

Abstract

The growth of two-dimensional materials by low-cost atmospheric pressure chemical vapour
deposition (AP-CVD) is explored in this thesis, with an emphasis on understanding key
features of the growth process. In particular, the growth of graphene on copper foils using
a methane precursor, MoS2 on natively oxidised silicon and MoS2 on graphene, graphite
and graphene ‘paper’ were studied. The resulting few-layer, monolayer and sub-monolayer
films were characterised by a combination of Raman spectroscopy (RS), Scanning Electron
Microscopy (SEM) and X-ray photoelectron spectroscopy (XPS).
Through varying the methane flow rate, it was found that there is no self-limitation to
graphene growth at high methane concentrations, resulting in graphene multilayers that can
delaminate from the copper substrate. The effect of a number of surface pre-treatments on
graphene growth is also presented. Nitric acid etching of copper foil was found to produce a
superior growth surface in comparison with those prepared with acetic acid or electropolishing, evidenced by a reduction in nucleation density and increased island size. Raman spectra
showed a remarkable correlation with these observations, indicating increased hole doping
with improved sample treatment. Therefore, Raman spectroscopy may be used as a probe
for the effectiveness of surface preparation. Several different approaches to the growth of
MoS2 on natively oxidised silicon by AP-CVD using S and MoO3 precursors are presented.
It was found that the growth of MoS2 was strongly dependent on the timing with which a
sufficient sulphur flux is introduced into the growth region. These results led to an investigation into the influence of sulphur partial vapour pressure on MoS2 growth. It was found
that MoS2 coverage decreased with increasing sulphur vapour pressure. These results could
be successfully rationalised by the Langmuir-Hinshelwood model of growth kinetics, which
is usually applied to reactions on well-defined crystalline surfaces and had not previously
been considered for MoS2 growth. XPS was used to study the composition of AP-CVD
grown MoS2 as a function of sulphur evaporation temperature and provided clear evidence
that lower sulphur vapour pressure leads to an increased concentration of sulphur vacancy
defects.
Attempts were made to grow MoS2 directly on highly oriented pyrolytic graphite as a
model substrate. MoS2 was found to grow on graphite under similar conditions to those
for natively oxidised silicon, but nucleation was observed to occur primarily at a defect (step)
sites. Attempts to grow MoS2 directly on graphene CVD grown on copper, commercially
sourced graphene powder, and graphene paper are also reported.