Chemistry Reference
In-Depth Information
Graphene was realized experimentally in 2004 (Novoselov et al.
2004
). Since
then, there has been intense interest in this material, stemming both from graphene's
unusual physical properties and from the possible applications of graphene in high-
speed analogical or digital electronics, electro-mechanical systems, sensors, energy
storage, etc (Lee et al.
2010
). In particular, the high mobility of electrons in
graphene and the strong electric field effect encourage work to realize graphene-based
electronics (Wu et al.
2008
).
Graphene is manufactured mainly in three ways: by exfoliation from HOPG (Hale
et al.
2011
), by the epitaxial growth in silicon carbide (Wu et al.
2009
) and by the
epitaxial growth on metals (Politano et al.
2011a
,
b
; Borca et al.
2010
; Martoccia
et al.
2010
). The initial methods of preparation of graphene by peeling graphite or
vaporizing SiC suffered from an inherent lack of control and were not scalable and
they have been replaced almost universally by methods to grow controlled epitaxial
graphene on different substrates.
Graphene layers were grown on the surfaces of many transition metals upon
annealing in a hydrocarbon atmosphere. What is nowadays a technique, was an
unwanted side effect in catalytic processes, as it lead to the passivation of catalysts,
known as poisoning. The chemical deposition of carbon on metal substrates has
been extensively studied from the 1970s to 1990s (Shikin et al.
1998
,
1999
). A major
motivation for studying these graphite films was the passivation of catalysts by carbon
films known as poisoning, but the properties of graphene were not investigated in
detail.
The epitaxial growth of large, highly perfect graphene monolayers is indeed a
prerequisite for most practical applications of this “wonder” material. Most of these
epitaxial graphene layers are spontaneously nanostructured in a periodic array of
ripples by the Moiré patterns caused by the difference in lattice parameter with the
different substrates such as Ru(0001) (Borca et al.
2010
), Ir(111) (Müller et al.
2011
)
or Pt(111) (Politano
2011c
,
d
;
2012a
,
b
,
c
). The careful characterization of these
superlattices is important because nanostructuring graphene (in superlattices, stripes
or dots), in turn, may reveal new physical phenomena and fascinating applications.
In addition, it is crucial to understand the interaction of graphene with the surfaces
of substrates of different nature (oxides, semiconductors or metals), as well as with
adsorbed molecules, in view of the relevance of metallic contacts, and the sensitivity
of the conduction properties of graphene to gating materials and doping by adsorbed
molecules (Politano
2011a
,
c
).
All these topics can be characterized in detail in what has become on of the
benchmarks for epitaxial graphene: a self-organized, millimeter large, periodically
“rippled” epitaxial monolayer of graphene grown by soft CVD under UHV conditions
on single crystal metal substrates with hexagonal symmetry. The superb control that
allows the UHV environment facilitates the characterization of the system down to
the atomic scale.
In this chapter we report on HREELS investigations on both the vibrational and
electronic properties of graphene grown on Pt(111).
