Synthesis of graphene nanoribbons on Ge(001) by chemical vapor deposition using methane, ethylene, and benzene precursors

Graphene nanoribbons (GNRs) offer the possibility of combining the exceptional carrier mobility of graphene with a width- and edge-tunable bandgap, enabling semiconducting behavior essential for nanoelectronic and optoelectronic devices. Anisotropic chemical vapor deposition of GNRs on Ge(001) has emerged as a promising avenue for synthesizing high-aspect ratio, aligned GNRs with faceted armchair edges on technologically relevant substrates, yet the influence of carbon precursor on growth outcomes remains unexplored. Here, we present a systematic comparison of GNR synthesis on Ge(001) using methane (CH4), ethylene (C2H4), and benzene (C6H6) as feedstocks. The choice of precursor significantly impacts GNR growth rates, anisotropy, and structural quality. CH4 yields the highest-aspect ratio ribbons, while C2H4 and C6H6 produce lower-aspect ratio ribbons presumably due to the multi-carbon active species they generate, lowering the barrier for nucleating new atomic rows when being incorporated into the growing edges of GNRs. These findings establish direct links between precursor chemistry and GNR growth characteristics, offering opportunities for further optimization and tailored synthesis.