Suppression of Grain Boundaries in Graphene Growth on Superstructured Mn-Cu(111) Surface

As undesirable defects, grain boundaries (GBs) are widespread in epitaxial graphene using existing growth methods on metal substrates. Employing density functional theory calculations, we first identify that the misorientations of carbon islands nucleated on a Cu(111) surface lead to the formation of GBs as the islands coalesce. We then propose a two-step kinetic pathway to effectively suppress the formation of GBs. In the first step, large aromatic hydrocarbon molecules are deposited onto a $\sqrt{3}\times \sqrt{3}$ superstructured Cu-Mn alloyed surface to seed the initial carbon clusters of a single orientation; in the second step, the seeded islands are enlarged through normal chemical vapor deposition of methane to form a complete graphene sheet. The present approach promises to overcome a standing obstacle in large scale single-crystal graphene fabrication.

Figure 1

(a) and (b) Structural illustrations of the Cu(111) substrate and graphene, where the dashed lines show their respective high-symmetry axes. (c) and (d) Illustrations of two geometries where a 7CR carbon cluster is at a HSO on the Cu(111) surface. In (c), the edge C atoms reside at the threefold hollow sites; in (d), the edge C atoms are at the bridge sites between two surface Cu atoms.

Figure 2

Side and top view of a 7CR carbon cluster on the Cu(111) surface, illustrating the domed nature (a) and the rotated nature (b) from the HSO of Fig. 1c, respectively.

Figure 3

(a) Structure of the ($\sqrt{3}\times \sqrt{3}$) $R30°$ Mn-Cu(111) superstructurally alloyed surface. (b)–(d) Three stable or metastable geometries of a 7CR carbon cluster adsorbed on the Mn-Cu(111) surface. As indicated by the dashed lines, (b) and (c) illustrate two HSO configurations, while (d) is rotated from a HSO, and their relative stabilities are indicated by their total energy differences.

Figure 4

Enlargement of coronene-seeded carbon islands via conventional CVD growth. The individual C adatoms supplied in the second step of the seed and grow kinetic pathway diffuse and attach to the nearby islands to fill the opening spaces, resulting in a larger graphene sheet with no GBs.