Graphene, known as the thinnest two-dimensional nanomaterial, is commonly synthesized on transition metal foils such as copper, nickel, iron and cobalt for a range of applications, including electronics, energy storage, and catalysis. In this study, we present a novel, patented method that uses biochar as a renewable precursor for graphene growth on metal foils. Biochar is placed on iron and cobalt foils and heated to 1000°C in an electric quartz tube furnace. At this temperature, carbon atoms from biochar dissolve into the metal catalyst, forming stable carbides. Upon cooling, these carbides become unstable and precipitate, leading to the formation of graphene at the eutectic temperature. Unlike conventional chemical vapor deposition (CVD) methods, this approach allows for the simultaneous growth of graphene on both sides of the metal foils without the use of vacuum and hydrogen. X-ray diffraction (XRD) analysis confirmed the presence of graphene on both iron and cobalt foils, with multi-layer graphene observed on the iron foil, as well as metastable iron carbide (Fe₃C), which stabilizes below the eutectoid temperature of iron (727°C). Graphene coverage was improved by changing experimental parameters. Raman spectroscopy was employed to assess the distribution of single and multi-layer graphene on the metal foils. The Raman spectra were analyzed at various points on the surface to differentiate between single-layer and multi-layer graphene based on the characteristic peaks of the D, G, and 2D bands. The intensity ratio of the 2D and G bands was used to estimate the number of graphene layers, with single-layer graphene exhibiting a sharp 2D peak and a distinct intensity ratio compared to multi-layer graphene. However, due to the gradual decrease in the 2D/G ratio beyond 5 layers, Raman spectroscopy becomes less effective at accurately estimating the number of layers beyond this point. Grazing incidence small-angle X-ray scattering (GISAXS) will be employed to further investigate the structural properties of the graphene films. GISAXS, like traditional SAXS, involves directing X-rays at a very shallow angle to probe the surface and subsurface regions of the sample. The resulting scattering pattern provides insight into the surface-roughness, film thickness, and structural organization of the material. By measuring the interlayer spacing (d) of the graphene, GISAXS allows for the estimation of the number of graphene layers, as graphene exhibits characteristic interlayer spacing that can be observed in the diffraction pattern. GISAXS offers a more direct measurement of layer thickness and interlayer spacing, providing quantitative data on graphene layer characteristics, while Raman spectroscopy provides complementary qualitative insights into the nature and distribution of graphene on the foils. The comparison of both techniques will demonstrate the strengths and limitations of each method, with GISAXS offering high spatial resolution for film thickness and interlayer measurements, and Raman spectroscopy providing real-time, localized analysis of graphene quality and layer distribution.
