Laser-induced etching of few-layer graphene synthesized by Rapid-Chemical Vapour Deposition on Cu thin films
Marco Piazzi
0
1
Luca Croin
1
2
Ettore Vittone
0
Giampiero Amato
1
0
Department of Physics, NIS Centre of Excellence and CNISM, University of Turin
, Via Pietro Giuria 1, 10125 Turin,
Italy
1
Quantum Research Laboratory, Istituto Nazionale di Ricerca Metrologica
, Strada delle Cacce 91, 10135 Turin,
Italy
2
Department of Applied Science and Technology
, Politecnico of Turin, Corso Duca deli Abruzzi 24, 10129 Turin,
Italy
The outstanding electrical and mechanical properties of graphene make it very attractive for several applications, Nanoelectronics above all. However a reproducible and non destructive way to produce high quality, large-scale area, single layer graphene sheets is still lacking. Chemical Vapour Deposition of graphene on Cu catalytic thin films represents a promising method to reach this goal, because of the low temperatures (T < 950C1000C) involved during the process and of the theoretically expected monolayer self-limiting growth. On the contrary such self-limiting growth is not commonly observed in experiments, thus making the development of techniques allowing for a better control of graphene growth highly desirable. Here we report about the local ablation effect, arising in Raman analysis, due to the heat transfer induced by the laser incident beam onto the graphene sample.
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Graphene (a single bidimensional layer of carbon atoms
arranged in an hexagonal lattice) has attracted a major
interest in the last few years because of its astonishing
electrical (Castro Neto et al. 2009; Peres 2010; Peres
et al. 2006), mechanical (Lee at al. 2008) and chemical
properties (Elias et al. 2009; Wang et al. 2009a), that
make it a good candidate for the future development of
nanoelectronics devices. Although the main properties
of this material are nowadays well known from a
theoretical point of view, an efficient and highly reproducible
method to grow high quality, large-scale area, single layer
graphene films, suitable for practical applications, is still
lacking. For this reason, several techniques have been
developed in the last years in order to achieve this goal:
the most important are the epitaxial growth of graphene
by thermal sublimation of SiC (de Heer et al. 2007; Emtsev
et al. 2009; Hass et al. 2008; Sprinkle et al. 2009; Varchon
et al. 2007), the Chemical Vapour Deposition (CVD)
synthesis of graphene on various metal catalysts (Reina et
al. 2009; Lee et al. 2010; Liu et al. 2010; Kim et al. 2012;
Nandamuri et al. 2010; Somani et al. 2006; Li et al. 2009a;
2009b; Tao et al. 2012) and the chemical reduction of
graphene oxide (Gilje et al. 2007; Lee at al. 2009; Paredes
et al. 2008; Schniepp et al. 2006). Among these, CVD
technique seems to be one of the most promising
methods because of the reported possibility (Liu et al. 2010)
of obtaining highly uniform, defect-free graphene flakes
as large as 100 m2 in a reproducible, highly accessible
and inexpensive way.
Since CVD synthesis needs a catalyst to activate the
chemical decomposition of the carbon precursor (usually
methane or ethylene) used for graphene growth at low
temperatures (T < 950C 1000C), the use of many
metals (Ir (Coraux et al. 2008), Ru (Martoccia et al.
2008), Pt (Sasaki et al. 2000; Starr et al. 2006), Fe
(Kondo et al. 2010), Ag (Di et al. 2008), Ni (Liu et al.
2010; Kim et al. 2009; Obraztsov et al. 2007), Cu
(Bae et al. 2010; Li et al. 2009a; Tao et al. 2012) as
catalysts during the process has been reported in
literature. Cu is one of the most promising catalyst (Mattevi
et al. 2011) because of the low C solid solubility in it
(0.001 0.008 weight % at 1084C): this property
brings to the formation of only soft (not covalent) bonds
between the electrons of 2pz orbitals of sp2 hybridized
C atoms and the 4s electrons of Cu, without formation of
any carbide phase during the growth process. As a
consequence, formation of graphene should stop after one
single layer has been formed: this makes CVD growth of
graphene on Cu very attractive. Nonetheless, many
experiments show that actually such a self-limiting behaviour
is hardly observed, since few-layered graphitic structures
are usually grown on Cu substrates.
For this reason, to obtain monolayer graphene, several
post processing techniques have been proposed to
selectively etch atomic graphene layers. Among the various
approaches (e.g. heat-induced etching by oxygen (Liu et al.
2008), e-beam lithography assisted technique (Novoselov
et al. 2004; Zhang et al. 2005), graphene cutting by
carbonsoluble metals (Campos et al. 2009; Datta et al. 2008)
the thinning of atomic carbon multilayers by laser
irradiation (Han et al. 2011) can be a promising method to
obtain monolayer graphene. In this last work, authors
show how the central role in graphene etching is held both
by the laser irradiation used for the Confocal Raman
Spectroscopy performed on the samples, and by the SiO2/Si
substrate on top of which few-layered graphene has been
transferred: the heat produced by the irrad (...truncated)