Effects of annealing on copper substrate surface morphology and graphene growth by chemical vapor deposition Ahmed Ibrahim a , Sultan Akhtar a , Muataz Atieh b , Rohit Karnik c , Tahar Laoui a,⇑ a Department of Mechanical Engineering, King Fahd University of Petroleum & Minerals, Dhahran 31261, Saudi Arabia b Qatar Environment and Energy Research Institute, Qatar Foundation, 5825 Doha, Qatar c Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, United States article info Article history: Received 15 February 2015 Received in revised form 23 June 2015 Accepted 24 June 2015 Available online 29 June 2015 abstract Understanding the mechanism of graphene synthesis by chemical vapor deposition and the effect of pro- cess parameters is critical for production of high-quality graphene. In the present work, we investigated the effect of H 2 concentration during annealing on evolution of Cu surface morphology, and on deposited graphene characteristics. Our results revealed that H 2 had a smoothening effect on Cu surface as its sur- face roughness was reduced significantly at high H 2 concentration along with the formation of surface facets, dents and nanometer-sized particles. Furthermore, H 2 content influenced the graphene morphol- ogy and its quality. A low H 2 concentration (0% and 2.5%) during annealing promoted uniform and good quality bilayer graphene. In contrast, a high concentration of H 2 (20% and 50%) resulted in multilayer, non-uniform and defective graphene. Interestingly, the annealed Cu surface morphology differed consid- erably from that obtained after deposition of graphene, indicating that graphene deposition has its own impact on Cu surface. Ó 2015 Elsevier Ltd. All rights reserved. 1. Introduction Graphene, a monoatomic layer of carbon atoms in the form of honey-comb lattice has attracted much attention due to its remark- able structure, properties and potential applications in science and technology [1,2]. It has been also reported that graphene mem- branes with controlled-size pores could have great potential in gas and liquid- phase separation applications [3,4]. Graphene can be synthesized using different techniques such as liquid-phase exfoliation [5], mechanical exfoliation [6] and chemical vapor depo- sition (CVD). Synthesis of graphene by CVD is one of the most promising routes for producing large-area and good quality gra- phene films on suitable substrates [7]. Synthesis of graphene using CVD consists of four steps; heating, annealing, graphene deposition, and cooling. Gas flow rates (e.g. H 2 , Ar and CH 4 ) need to be selected carefully during each step to deposit graphene with desired charac- teristics. Copper (Cu) and nickel (Ni) are the most commonly used substrates/catalysts for graphene fabrication. Cu is extensively used as it promotes more uniform, relatively large-area graphene com- pared to that obtained on Ni substrate [8,9]. Cu is annealed in order to improve its surface characteristics by reducing surface oxides, volatile impurities and surface contaminations [10,11]. The surface morphology of annealed Cu substrate comprises many features such as roughness, grain boundaries, defects and impurity particles [11]. These features play a critical role on nucleation and growth mechanisms of graphene. For instance, Cu terraces (flat regions) favor formation of mono- or bi-layer graphene domains, while ledges (slope regions) promote multilayer graphene [12]. Moreover, grain boundaries, impurities and Cu particles (originated along surface scratches during pre- heating step) contribute to formation of multilayer graphene domains [11]. These features could also trap high amount of decomposed carbon species favoring deposition of amorphous or turbostatic graphene regions [13]. Thus, the quality of graphene film strongly relies on the surface morphology of underlying Cu substrate [14]. In recent years, an extensive work has been conducted to improve the quality of Cu substrate by minimizing its surface irreg- ularities and/or controlling the density of active nucleation sites. This goal was accomplished by various surface treatment methods, applied on Cu surface prior to CVD process, including chemical mechanical polishing [11], electro-polishing [15], and chemical pre-treatment using different etchants to remove surface impuri- ties [16]. However, such techniques can make Cu surface prepara- tion more complicated and add additional impurities. Some researchers melted the Cu substrate during annealing (before gra- phene growth) to minimize the effect of grain boundaries [17]. http://dx.doi.org/10.1016/j.carbon.2015.06.067 0008-6223/Ó 2015 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail address: tlaoui@kfupm.edu.sa (T. Laoui). CARBON 94 (2015) 369–377 Contents lists available at ScienceDirect CARBON journal homepage: www.elsevier.com/locate/carbon