Soot formation in combustion is a major research problem because of the negative impact of the carbonaceous particles in the exhausts on human health and the environment. However, state of the art knowledge on the chemical species and reaction pathways leading to the formation of soot particles is not yet complete. In particular, many questions are still open on the transformation of gaseous molecular precursors into condensed phase soot particles (soot nucleation). One of the hypotheses proposed in the literature, the nucleation driven by the dimerization of small polycyclic aromatic hydrocarbons (PAHs), has been recently used in models to successfully reproduce the soot volume fraction profiles measured in laboratory flames. However, experimental evidences on the existence of dimers in the flame environment are still lacking. In this work, Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) and high-resolution Atomic Force Microscopy (AFM) are coupled with the aim of characterizing the chemistry of the building blocks involved in the formation of nascent soot particles.