Combined microscopic and spectroscopic insights into the on-surface synthesis of graphene nanoribbons

Graphene nanoribbons (GNR) constitute a rapidly growing class of novel fascinating materials. Controlling the properties of GNR often implies controlling their atomic structure. In order to exert this control, a bottom-up approach for the growth of GNR is commonly used. Despite its great success, a lack of mechanistic understanding of the on-surface chemical processes remains one of the main challenges hindering further progress in the GNR synthesis. The most important question is how the properties of the underlying metal substrate and the precursor molecule affect the reaction pathway. A multitechnique approach utilizing complementary microscopic and spectroscopic methods is highly efficient for revealing the details of nanostructure formation on surfaces. This article is aimed at demonstrating that this approach enables a reliable monitoring of the on-surface chemical transformations upon GNR formation, thereby opening up a route to the design of GNR with targeted structure and properties. By referring to recent examples it is shown that a combination of X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure spectroscopy (NEXAFS) can provide chemical sensitivity necessary to complement structural information routinely obtained with scanning tunneling microscopy (STM). This combination of techniques is especially powerful in identifying different stages of the GNR growth processes and revealing various factors affecting reaction pathways.