APPLIED PHYSICS LETTERS 100, 021601 (2012)
Rafik Addou,1 Arjun Dahal,1 Peter Sutter,2 and Matthias Batzill1,a)
1Department of Physics, University of South Florida, Tampa, Florida 33620, USA
2Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, New York 11973, USA
(Received 4 November 2011; accepted 12 December 2011; published online 9 January 2012)
In contrast to the commonly employed high temperature chemical vapor deposition growth that
leads to multilayer graphene formation by carbon segregation from the bulk, we demonstrate that
below 600 ꢀC graphene can be grown in a self-limiting monolayer growth process. Optimum
growth is achieved at ꢁ550 ꢀC. Above this temperature, carbon diffusion into the bulk is limiting
the surface growth rate, while at temperatures below ꢁ500 ꢀC a competing surface carbide phase
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impedes graphene formation. 2012 American Institute of Physics. [doi:10.1063/1.3675481]
Graphene synthesis by chemical vapor deposition
(CVD) on late transition metal substrates, such as Cu,1 Ni,2
Ru,3 Ir,4 or Pt,5 is a promising approach for the synthesis of
large area graphene wafers.6,7 The low carbon solubility in
copper leads to a desirable self-limiting surface growth of
graphene,7,8 while on other materials, including Ni, carbon
dissolution into the bulk at typical high growth temperatures
of 900 ꢀC can result in carbon re-segregation and multilayer
graphene formation upon cooling.9,10 On copper, the high
temperatures needed for graphene growth are close to its
melting temperature, resulting in copper sublimation and sur-
face roughening during growth.11 Furthermore, the weak
interaction between graphene and copper causes the forma-
tion of multiple graphene-domains with different orienta-
tions12 and therefore twist domain boundaries in graphene
cannot be avoided even on single crystalline copper sub-
strates. Nickel has been originally suggested for graphene
synthesis2,13 and would have some advantages over copper if
multilayer graphene formation could be avoided. For
instance, because of a stronger graphene-metal interaction
and better lattice match, graphene is in registry with Ni(111)
(Ref. 14) and consequently only one graphene-domain-rota-
tion exists for graphene grown on single crystalline Ni.
Therefore, no tilt-grain boundaries are expected after the co-
alescence of graphene domains to a closed film.15 Here, we
demonstrate by real-time observations in a low energy elec-
tron microscope (LEEM) that graphene with large (several
tens of lm2) domains can be grown effectively in surface
growth mode at relatively low substrate temperatures
(ꢁ550 ꢀC) and therefore a similar self-terminating mono-
layer growth as for copper can be achieved.
Ni(111). Above 650 ꢀC, the graphene layer starts to disinte-
grate in agreement with previous electron spectroscopy
results.13,16 This stability temperature of graphene sets an
upper limit for the growth temperature of graphene in a sur-
face growth mode on nickel. At low temperatures (<400 ꢀC),
a surface carbide phase is formed. Our previous AES studies
demonstrated that this surface carbide phase is stable up to
ꢁ480 ꢀC.13 This carbide phase impedes the nucleation and
growth of graphene. Therefore, in this study, we chose three
growth-temperatures, 500 ꢀC, 550 ꢀC, and 600 ꢀC, which lie
in between the phase stability limits of the surface-carbide
and graphene.
Figure 2 shows LEEM images and AES spectra of the
surface at different ethylene exposures at 500 ꢀC. LEEM
shows the onset of a transformation of the clean Ni(111) sur-
face into a different surface phase for 5-100L exposures.
From correlation with AES measurements, we can identify
this phase as the ordered monolayer surface carbide previ-
ously discussed in detail.13,17 The first graphene nucleation
is observed after increasing the ethylene exposure to 760L.
At 500 ꢀC, the growth front of these graphene islands advan-
ces at an initial rate of ꢁ5.5 nm/s. In the LEEM movies, we
cannot identify any separation between the advancing gra-
phene grain and the Ni2C phase. Therefore, it is possible that
graphene grows by a direct conversion of the carbide in
agreement with previous scanning tunneling microscopy
(STM) studies.18
We have grown graphene by ultrahigh vacuum (UHV)
chemical vapor deposition with ethylene (C2H4) as the pre-
cursor molecule at a pressure of 10À6 Torr. The growth of
graphene on the Ni(111) single crystal was monitored with a
Elmitec V LEEM and with Auger electron spectroscopy
(AES) using a double pass cylindrical mirror analyzer in two
separate UHV systems. Figure 1 shows LEEM studies for
determining the thermal stability of graphene monolayers on
FIG. 1. LEEM images illustrating the thermal stability of monolayer gra-
phene on Ni(111). (a) shows a Ni(111) surface almost entirely covered by
graphene (dark areas are uncovered Ni-substrate) at a sample temperature of
605 ꢀC. Upon raising the temperature to 655 ꢀC, the graphene sheet is start-
ing to dissolve as shown in (b).
a)Author to whom correspondence should be addressed. Electronic mail:
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100, 021601-1
2012 American Institute of Physics