Defect-like Structures of Graphene on Copper Foils for Strain Relief Investigated by High-Resolution Scanning Tunneling Microscopy

Abstract

Understanding of the continuity and the microscopic structure of as-grown graphene on Cu foils through the chemical vapor deposition (CVD) method is of fundamental significance for optimizing the growth parameters toward high-quality graphene. Because of the corrugated nature of the Cu foil surface, few experimental efforts on this issue have been made so far. We present here a high-resolution scanning tunneling microscopy (STM) study of CVD graphene directly on Cu foils. Our work indicates that graphene can be grown with a perfect continuity extending over both crystalline and noncrystalline regions, highly suggestive of weak graphene-substrate interactions. Due to thermal expansion mismatch, defect-like wrinkles and ripples tend to evolve either along the boundaries of crystalline terraces or on noncrystalline areas for strain relief. Furthermore, the strain effect arising from the conforming of perfect two-dimensional graphene to the highly corrugated surface of Cu foils is found to induce local bonding configuration change of carbon from sp(2) to sp(3), evidenced by the formation of "three-for-six" lattices.

Strain and curvature induced evolution of electronic band structures in twisted graphene bilayer

“…The average height and width (peak width at half-height) of the wrinkle are about 7.9 and 8.2 nm, respectively. For a corrugated twisted graphene bilayer with a small curvature, we can observe moiré superstructures along wrinkles and ripples 37,38 ( Supplementary Fig. S3).…”

“…The twisted graphene bilayer was grown on a 25-mm-thin Rh foil via a traditional ambient pressure chemical vapour deposition method 26 , and only the sample mainly covered with two graphene layers was further studied by STM and STS. Owing to the thermal expansion mismatch between graphene and the substrate, defect-like wrinkles and ripples tend to evolve along the boundaries of crystalline terraces for a strain relief 11,14,37,38 . Briefly, the sample was synthesized at 1,000°C and after growth when the sample is cooled down the graphene expands while the Rh foil contracts.…”

Graphene Induced Surface Reconstruction of Cu

“…They are also more irregularly spaced, with much larger sizes and separations than our dark lines. 31,32 The periodicity of the Moirépattern is sensitive to its orientation, 27,33 whereas our stripe pattern maintains its periodicity even with an orientation change (Figure 1c). Furthermore, the dark lines in our stripe pattern are not perfectly straight and can also show occasional bending or curvatures (as seen in Figures 1a,c and 2a), unlike the highly straight lines that would be produced by a lattice superstructure from the Moirépattern.…”

“…The graphene wrinkles or ripples typically appear as surface protrusions, 31,32 not depressions. They are also more irregularly spaced, with much larger sizes and separations than our dark lines.…”

Molecular dynamics simulation of graphene on Cu (1 0 0) and (1 1 1) surfaces

“…5. [42,43,45], Pt [44], Ni [44,46], SiC [47] and, somewhat less clearly recognisable on rougher surfaces, on Cu [48] and…”