Since graphene was discovered in 2004, the extraordinary characteristics of
graphene, which had been already theoretically predicted, were experimentally
verified. Among the graphene synthesis methods, chemical vapor deposition (CVD)
method has been recognized as the best candidate for obtaining high-quality graphene.
CVD graphene exhibits excellent electrical, optical and mechanical characteristics.
Based on these outstanding properties, CVD graphene has been received attentions
for next-generation device applications. Even though high-quality and large-area
graphene can be successfully synthesized by using CVD method, there are still
challenges to overcome toward industrial commercialization of graphene. For
example, it requires high growth temperature (T ~ 1,000 ℃) for decomposition of
methane on Cu catalyst. It indicates that this process costs a tremendous amount for
synthesis of graphene. Also, the neighbor material can be contaminated by thermally
evaporated Cu atoms, due to the low melting temperature of Cu (Tm ~ 1,085 ℃). It
critically hinders integration of technology development with Si-based standard processes. Furthermore, graphene grown on Cu surface is necessary for transfer
process to the target substrate. During this transfer stage, a lots of defects are
inevitably generated such as wrinkles and torn cracks. It seriously degrades the
performance of graphene-based electronic devices. To overcome previously
mentioned problems, the research related with low temperature/direct growth of
graphene on insulators have been widely studied for industrial commercialization.
Especially, a solid type of polycyclic aromatic hydrocarbons (PAHs) is the best
candidate for overcoming above challenges due to controllability of growth
temperature of graphene and interfacial adhesion force.
In Chapter 2, one of the important issues in CVD, low temperature growth of
graphene is studied. Until PAHs has not been introduced for carbon source, methane
has been conventionally used for main carbon source at extremely high temperature
(T ~ 1,000 ℃) due to high energy for dehydrogenation of methane. By using PAHs as
carbon source, the growth temperature rapidly reduced which satisfies the industrial
commercialization requirement. However, their unique molecule structure is
attributed to generate structural defects in graphene and they critically degrade the
device performances. To reduce these types of defects, the structural defect generation
mechanism is investigated and two types of defect generation mechanism are
suggested in chapter 3. Based on our suggested models, a short aliphatic carbon source,
1-octylphosphonic acid (OPA), is introduced for expectation of supplying carbon
fragments to the defect sites. Finally, the graphene grown by this method, using
TPN/OPA heterogeneous mixture as carbon sources, exhibits improved electrical
characteristics. The measured carrier mobilities of graphene from fabricated graphene
field-effect transistors are 210 cm2/V·s 1,074 cm2/V·s, respectively. It indicates that
the graphene grown by this suggested method can provide a simple and facile method
to produce graphene with high-quality at low temperature.
In Chapter 3, as a feasible candidate for graphene growth precursor, one of the
III
PAH is investigated for carbon source. A 1,2,3,4-tetraphenylnaphthalene (TPN) is
deposited as thin film on the substrate, UV/Ozone is exposed to the TPN deposited
substrate for enhancing the interfacial adhesion force between TPN and substrate. The
change of interfacial chemistry due to the UV/Ozone exposure is investigated through
X-ray photoelectron spectroscopy (XPS). It is confirmed that UV/Ozone exposure
generates some interfacial adhesion bonding (IAB) which is attributed to improve the
adhesion between UV/Ozone treated TPN and substrate. Furthermore, the
enhancement of interfacial adhesion successfully leads to prevent sublimation, then it
is directly converted graphene on target substrate. The graphene derived from this
method exhibits excellent environmental stability and electrical characteristics. Under
harsh environmental conditions such as ultra-sonication in water bath and dipping in
sulfonic acid, it maintains initial properties whereas transferred graphene does not
retain. Based on these properties, directly-grown graphene is used for transparent
electrode of organic field-effect transistors.