Atomic Hydrogen Promotes Polyparaphenylene Fusion into Graphene Nanoribbons on Au(111)

Graphene nanoribbons (GNRs) hold significant potential for applications in semiconductor electronics. Compared to precursor design, the lateral fusion of polymers offers a versatile and flexible approach to producing GNRs with desirable properties. Developing effective methods to enhance lateral fusion is therefore highly desirable. In this study, the beneficial effects of atomic hydrogen (AH) are reported in promoting the lateral fusion of polyparaphenylene (PPP) chains into GNRs on Au(111). When PPP chains are treated with AH at 570 K, the threshold temperature for GNR formation by lateral fusion is reduced to 590 K, a substantial decrease from the 650 K required for the formation of GNR by postannealing without AH. The promoting effect of AH is attributed to the superhydrogenation of PPP chains at 570 K, which 1) locally disrupts π-aromaticity, and 2) facilitates closer proximity of PPP chains. Both effects aid in the dehydrogenative C-C coupling of PPP chains. Scanning tunneling microscopy (STM) and synchrotron radiation photoemission spectroscopy (SRPES) are used to identify reaction products and monitor reaction pathways. The demonstrated role of AH in this study may be extended to other systems involving the lateral fusion of polycyclic aromatic hydrocarbon (PAH)-based polymers.