Oxide-assisted growth of scalable single-crystalline graphene with seamlessly stitched millimeter-sized domains on commercial copper foils

Abstract

Chemical vapor deposition (CVD) is considered as an effective route to obtain large-area and high-quality polycrystalline graphene; however, there are still technological challenges associated with its application to achieve single crystals of graphene. Herein, we present the CVD growth of scalable single-crystalline graphene by seamless stitching millimeter-sized unidirectional aligned hexagonal domains using different types of commercial Cu foils without repeated substrate polishing and H₂-annealing processes. Compared with that reported in previous studies, herein, the average size for the hexagonal graphene domains is enlarged by 1-2 orders of magnitude (from tens of micrometers to millimeter). The key factor for growth is the Cu surface monocrystallization achieved by a pre-introduced oxide layer and the sequential Ar annealing. The graphene domains exhibit an average growth rate of >20 μm min^-1 and a misorientation possibility of <2%, and seamless stitching at the domain coalescence interfaces is confirmed by atomic force microscopy measurements.

Fig. 1. (a) Schematic of the CVD growth procedure. (b) The XRD measurements show that the Cu substrates before and after graphene growth are dominated by the (100) texture. (c) The EBSD results demonstrate an actual surface monocrystallization to the (111) texture for the Cu substrates. (d) An optical image for individual aHGDs grown for 60 min. (e) An SEM image for individual aHGDs grown for 30 min. (f) An OM image of a nearly continuous graphene film coalesced by aHGDs. The exposed Cu surfaces (dark orange areas) confirm the alignment of coalesced aHGDs. (g) Typical Raman spectrum of aHGDs indicates the monolayer nature and high quality of the sample.

Fig. 2. The OM image and scanning Raman spectroscopy results for the G, 2D, and D bands for an aHGD transferred onto the SiO₂/Si substrate. Scale bars: 100 μm.

Fig. 3. (a) The obtained OM image of aHGDs on the Cu surface over ∼1 cm² scanned area (growth time: 30 min). Only two Cu grain boundaries are visible in the image, demonstrating the high efficiency of oxide-assisted surface monocrystallization. (b) Histogram of the size distribution for aHGDs in (a), which follows Gaussian distribution. (c) Histogram of the orientation distribution for aHGDs in (a). Three different domain orientations are found in the three Cu grains, and only less than 1% graphene domains are misoriented in the same Cu grain.

Fig. 4. (a and b) OM images of the two coalesced aHGDs and their interface, respectively. (c) AFM measurements of lateral force (friction), current, and deflection (error signal) scanned from the region A of the aHGD interface in (b). No apparent signal differences are detected at the interface in all these images. (d) Atomic-resolution AFM images and their corresponding Fourier transform images from the region B and C in (a). The lattices in both regions exhibit the same orientation, demonstrating the unidirectional alignment of the aHGDs. (e) Lattice orientation detected from atomic-resolution AFM confirms the zigzag structure of the aHGD edges. Scale bar in (e): 0.1 nm.