Growth of large-area single- and Bi-layer graphene by controlled carbon precipitation on polycrystalline Ni surfaces

Abstract

We report graphene films composed mostly of one or two layers of graphene grown by controlled carbon precipitation on the surface of polycrystalline Ni thin films during atmospheric chemical vapor deposition (CVD). Controlling both the methane concentration during CVD and the substrate cooling rate during graphene growth can signifi cantly improve the thickness uniformity. As a result, one-or two-layer graphene regions occupy up to 87% of the fi lm area. Single layer coverage accounts for 5 % 11% of the overall fi lm. These regions expand across multiple grain boundaries of the underlying polycrystalline Ni fi lm. The number density of sites with multilayer graphene/graphite (>2 layers) is reduced as the cooling rate decreases. These fi lms can also be transferred to other substrates and their sizes are only limited by the sizes of the Ni fi lm and the CVD chamber. Here, we demonstrate the formation of fi lms as large as 1 in 2 . These fi ndings represent an important step towards the fabrication of large-scale high-quality graphene samples. KEYWORDS Graphene, chemical vapor deposition, nickel catalyst, carbon nanomaterialsAddress correspondence to jingkong@mit.edu Exploring ways to synthesize graphene which allow scalability, have low fabrication cost and facilitate integration with other materials, could play an important role in both fundamental research and the realization of future graphene applications. Several graphene synthesis approaches have been developed, including: (1) exfoliation methods (both mechanical [1,2] and chemical [3 8]); (2) graphitization of SiC surfaces [9,10]; (3) graphene precipitation/deposition on transition metal surfaces [11,12]; (4) gas phase/ substrate-free formation of graphene sheets [13]. Procedures such as (1) and (4) produce free-standing graphene isolated from any substrate which enables the integration of graphene with other materials. Methods like (2) and (3) produce graphene bound to a specific substrate which limits the flexibility of these approaches. Recently, it has been shown that graphene films can be grown by ambient pressure chemical vapor deposition (CVD) on thin films of transition metals and isolated from their growth Here, we present an important advance to further improve the thickness uniformity of these fi lms. We show that the area of multilayer graphene regions on the fi lm can be reduced and the regions with singleor bi-layer graphene (1 2 LG) can be increased to 87% of the overall fi lm area. The precipitation of monolayer and multilayer graphene from bulk transition metals is widely known [18,19]. It occurs due to the temperature-dependent solubility of carbon in transition metals. This concept has recently been used to produce 1 2 LG under either vacuum conditions [11,19] or in an ambient pressure CVD process [14 17]. In our process, carbon is introduced into the bulk of thin (~500 nm) Ni films by decomposing a highly diluted hydrocarbon gas (CH 4 ). Graphene precipitation is promoted on the surface of the Ni fi lms upon cooling of the Ni C ...

Rational design of a binary metal alloy for chemical vapour deposition growth of uniform single-layer graphene

“…1c) shows the excellent uniformity and 100% surface coverage of the graphene. From the green channel contrast with respect to the underlying SiO 2 /Si substrate in the optical microscope image 12 , we confirmed that all of the graphene area had a single layer, and no multilayer graphene was observed (please also see the RGB colour image in Supplementary Fig. S2).…”

“…1e). Interestingly, the best reported uniformity over Ni/SiO 2 /Si substrates was only 87% of single-or bilayer graphene 12 . On the popular Cu foils, the best growth results still contain about 5% of thicker-layer graphene 9 .…”

“…The general CVD process for growing graphene on metals involves the following elementary steps: adsorption and subsequent catalytic decomposition of a gaseous carbon source on metal surfaces, downward dissolution of surface carbon species into the bulk metal, upward segregation of the carbon atoms in the bulk metal onto the metal surface upon cooling and reconstruction of the surface carbon atoms into graphene 12,13 . The growth kinetics of graphene are further complicated by the growth pressure (typically low pressure or ambient pressure) and temperature, cooling rate, concentration of carbon sources and solubility of carbon and its temperature dependence in bulk metal [12][13][14][15][16] .…”

“…The growth kinetics of graphene are further complicated by the growth pressure (typically low pressure or ambient pressure) and temperature, cooling rate, concentration of carbon sources and solubility of carbon and its temperature dependence in bulk metal [12][13][14][15][16] . All of these factors contribute to the uniformity and layer distribution of the obtained graphene films.…”

“…Apparently, the cooling rates of the growth substrates strongly affect the graphene thickness and uniformity. Interestingly, the use of thin-metal films with slow cooling can suppress the excessive carbon precipitation 12 . In addition, improving the surface perfectness of the catalytic metals is effective for growing long-range ordered graphene, which has been demonstrated by recent works using heteroepitaxially deposited Ni on magnesium oxide (MgO) (111) 19 and highly crystalline Co thin film on c-plane sapphire 20 .…”