Catalytic substrates for graphene growth
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Introduction Graphene research has experienced tremendous growth in the past 13 years because of its unique fundamental properties and prospects for very promising applications.1 Techniques for the preparation of large-area graphene films at the centimeter or even meter scale, especially by chemical vapor deposition (CVD) of carbon precursors on catalytic substrates, have seen rapid progress.2 Graphene formation on catalytic substrates, especially metals such as Ni, Co, Ru, Pt, Rh, Pd, and Ir, has been the subject of several studies for more than 50 years.3 Rather than synthesizing graphene, many of these studies were concerned with poisoning the metal’s catalytic activity (i.e., metal catalysts lose their activity due to the formation of graphitic layers on their surface).4 Following the rediscovery of graphene by Novoselov and Geim in 2004,1 researchers have deliberately developed methods to produce large-area graphene films by revisiting existing carbon/metal systems such as Ru and Ni (Figure 1a–c).5–8 These systems, however, show difficulty in isolating graphene from the metal substrates or controlling the thickness uniformity. Li et al. introduced Cu in 2009 as a catalytic substrate for graphene growth by CVD from methane (Figure 1d–f).9,10 Since then, Cu (sometimes alloyed with other metals such as Ni) has emerged as a good choice for graphene synthesis due to its
advantages of being able to grow large-area and high-quality graphene with maximum control. Other graphene-film preparation techniques have also been developed, such as growing graphene on dielectric substrates11 and the growth of graphene foam.12 Understanding graphene growth on nonmetal substrates, especially the catalytic activity, is still in its infancy and therefore is not reviewed in this article. We focus on metal catalytic substrates for graphene growth by CVD, including graphene growth mechanisms and kinetics, control of the number of graphene layers and stacking order, engineering of large-area graphene single crystals, low-temperature growth, and associated challenges and prospects.
Graphene growth mechanisms and kinetics Generally, graphene growth on metals by CVD can be divided into the following steps (see Figure 2): (1) Carbon precursors are transported to the metal surface; (2) the precursor is adsorbed and catalytically decomposed into active C species; (3) the active C species diffuse on the surface or into the bulk; (4) C aggregates on the surface for nucleation; (5) C attaches graphene nuclei for growth; (6) catalytic decomposition of C precursors terminates once the substrate is fully covered with graphene; and (7) more graphene layers form by
Fangzhu Qing, University of Electronic Science and Technology of China, China; [email protected] Changqing Shen, University of Electronic Science and Technology of China, China; [email protected] Ruitao Jia, University of Electronic Science and Technology of China, China; [email protected] Longlong Zhan, University of Electronic Science and Technology of China, China; [email protected]
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