Triangular Graphene Grain Growth on Cube‐Textured Cu Substrates

Abstract

The growth of graphene has been carried out on cube-textured (100) oriented Cu (CTO-Cu) foils using chemical vapor deposition (CVD). Well-aligned triangular grains self-assembled on CTO-Cu during CVD heating in fl owing hydrogen. The nucleation of triangular graphene grains has been confi rmed. This demonstrates that the shape and possible alignment of the graphene grains can potentially be tuned by changing the properties of the substrate, which should ultimately lead to improved electrical properties of the graphene. This type of graphene nucleation and alignment is novel and has not been observed in previous studies on other copper foil samples. Dr symmetry of the (100) CTO-Cu, the shape and alignment of the triangles might be attributed to the infl uence of the in-plane texture of the CTO-Cu. The Growth and Characterization of Triangular Graphene Grains on CTO-CuThe growth of graphene initiated on the triangles after CH 4 was introduced into the CVD chamber immediately after the growth temperature of 1000 ° C was reached. A surface coating of this thickness (most probably amorphous copper oxide) would mask the ability to observe the crystalline nature of the copper substrate beneath the layer. This argument is supported by the uniform distribution of chemical elements C, O and Cu as shown in the line scans across a selected triangle in Figure 2 e using energy-dispersive X-ray spectrometry (EDS). The presence of oxygen may be attributed to absorbed gaseous molecules from residual air on Cu surface, which may be diffi cult to avoid considering CVD is a low vacuum process. This residual oxygen may form copper oxide on the surface as well, which could inhibit the nucleation of the graphene, except where that oxide is reduced, such as on the triangles. Considering the oxygen content has negligible variation across the triangles, the reduction may occur only on the surface of the triangles. A more detailed discussion will be given later.oriented traingles with several micrometers in dimension provide ideal nucleation sites for graphene epitaxy and the details of the expriment is described in the following. Results and Discussion The Effect of Annealing on the Morphologies of Cu FoilsFollowing the procedure in the Experimental Section, graphene fi lms have been grown using CVD on CTO-Cu substrates. The effect of annealing of the CTO-Cu was investigated by heating the substrate under a hydrogen fl ux for different lengths of time. The same heating procedure was applied to CTO-Cu and Poly-Cu foils for comparison. A heating rate of 20 ° C/min was adopted to heat the samples to 1000 ° C in H 2 fl ow followed by immediate cooling back to room temperature (cooling took about 2 hours) by turning off the furnace. Figure 1 compares the CTO-Cu and Poly-Cu surface morphology after the substrate had been heated to 1000 ° C in H 2 fl ow followed by cooling back to room temperature immediately without annealing process [ Figure 1 a] and after a 20 minute annealing at 1000 ° C [ Figure 1 b]. Triangles of a few μ m in dimension can...

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“…a) SEM images of triangular graphene grown on CTO‐Cu using the CVD method. Reproduced with permission . Copyright 2011, Wiley‐VCH.…”