Catalyst-free synthesis and deposition mechanism of vertically oriented graphene on aluminum foil using PECVD

The catalyst-free growth of vertically oriented graphene (VG) networks with growth rate of about 5 nm/min on commercial aluminum (Al) foil via radio frequency plasma-enhanced chemical vapor deposition (RF-PECVD) is reported. The effects of process parameters, including precursor type and deposition temperature, on VG synthesis were systematically investigated. The deposition temperature plays a decisive role in the formation of VGs, while the precursor primarily influences growth rate and crystallinity. VGs were synthesized using either ethylene (C₂H₄) or propylene (C₃H₆) as precursors, but formation does not occur at lower temperatures (e.g., 500 °C). Precursors that effectively generate carbon dimers and exhibit a higher H:C ratio are more favorable for achieving VGs with high growth rates and superior crystallinity. Furthermore, we proposed a deposition mechanism that encompasses both the growth of VGs on the Al foil surface and the diffusion of carbon atoms into the Al foil. The growth process of VGs follows three distinct stages: the formation of buffer carbon nanoislands, nucleation, and subsequent growth. X-ray photoelectron spectroscopy (XPS) revealed the chemical interactions between carbon, Al_xO_y, and metallic Al at the interface, resulting in a diffusion layer and an interface layer between the VG layer and the underlying Al substrate.