AB-stacked bilayer graphene films obtained on dilute Cu(Ni) foils using atmospheric pressure chemical vapour deposition

Abstract

Despite its favourability as a substrate in chemical vapour deposition (CVD), copper (Cu) substrate has a challenge of growing uniform large-area bilayer graphene films with continuous Bernal (AB) stacking. However, copper/nickel (Cu/Ni) thin films are known to grow uniform large-area AB-stacked bilayer graphene films. In this study, large-area or wafer-scale (on the scale of an entire foil) AB-stacked bilayer graphene films were prepared on commercial dilute Cu(0.5 at% Ni) foils (MaTeck) and Ni doped Cu foils (Alfa Aesar) using atmospheric pressure chemical vapour deposition (AP-CVD). The Ni doped concentration and the Ni distribution in dilute Cu(Ni) foils were confirmed with inductively coupled plasma optical emission spectrometry (ICP-OES) and Proton-induced X-ray emission (PIXE). The electron backscatter diffraction (EBSD) maps showed that foils have continuous (001) surface orientation (Alfa Aesar) and diverse crystallographic surface (MaTeck). The increase in Ni surface concentration in foils was investigated with time-of-flight secondary ion mass spectrometry (TOF-SIMS) and X-ray photoelectron spectroscopy (XPS). The quality of graphene, the number of graphene layers and the layers stacking order in synthesized bilayer graphene films were confirmed by Raman spectroscopy and electron diffraction measurements. A four point probe station was used to measure the sheet resistance of graphene films. In the Raman optical microscope images, a wafer-scale monolayer and large-area or wafer-scale bilayer graphene films were distinguished and confirmed with Raman spectra intensities ratios of 2D to G peaks. The Raman data and the electron diffraction data suggest a Bernal stacking order in the prepared bilayer graphene films. A four-point probe sheet resistance of graphene films confirmed a bilayer graphene film sheet resistance distinguished from that of monolayer graphene. Wafer-scale AB-stacked bilayer graphene films were obtained on prepared dilute Cu(Ni) alloy foils. However, in commercial dilute Cu(0.5 at% Ni) foils, only large-area AB-stacked bilayer graphene films on monolayer graphene background could be obtained and the diverse crystallographic surface of a foil (EBSD data) could be a reason for incomplete wafer-scale bilayer graphene film. Since different Cu surfaces grow graphene films with different thicknesses. For instance, high index Cu surfaces and low index Cu(001), Cu(101) surfaces are known to grow multilayer graphene and Cu(111) surface to grow monolayer graphene. This study clearly showed the capability of a dilute Cu(Ni) foil (Alfa Aesar) (prepared dilute Cu(Ni) alloy foil) for growing a wafer-scale AB-stacked bilayer graphene film (substrate size, 400 mm2) compared to a commercial Cu(0.5 at% Ni) foil (MaTeck) which showed large-area bilayer graphene ( 900 mm2) and a pure Cu foil which showed discrete bilayer graphene domains (lateral size of 10 mm) on a monolayer graphene background. The capability of a dilute Cu(Ni) foil for growing a wafer-scale AB-stacked bilayer graphene film was ascribed to the (001) continuous surface orientation of a foil and the metal surface catalytic activity of Cu and Ni in a dilute Cu(Ni) foil. The results obtained in this study demonstrate the interest and potential insight of using dilute Cu(Ni) alloy foils as substrates in CVD for the synthesis of large-area (or wafer-scale) AB-stacked bilayer graphene films. This study contributes substantially to the on-going research on the growth of high-quality large-area AB-stacked bilayer graphene films on metal substrates using CVD.