Incipient soot early in the flame was studied by high-resolution atomic force microscopy and scanning tunneling microscopy to resolve the atomic structure and orbital densities of single soot molecules prepared on bilayer NaCl on Cu(111). We resolved extended catacondensed and pentagonalring linked (pentalinked) species indicating how small aromatics cross-link and cyclodehydrogenate to form moderately sized aromatics. In addition, we resolved embedded pentagonal and heptagonal rings in flame aromatics. These nonhexagonal rings suggest simultaneous growth through aromatic cross-linking/cyclodehydrogenation and hydrogen abstraction acetylene addition. Moreover, we observed three classes of open-shell π-radical species. First, radicals with an unpaired π-electron delocalized along the molecule's perimeter. Second, molecules with partially localized π-electrons at zigzag edges of a π-radical. Third, molecules with strong localization of a π-electron at pentagonal-and methylene-type sites. The third class consists of π-radicals localized enough to enable thermally stable bonds, as well as multiradical species such as diradicals in the open-shell triplet state. These π-diradicals can rapidly cluster through barrierless chain reactions enhanced by van der Waals interactions. These results improve our understanding of soot formation and the products formed by combustion and could provide insights for cleaner combustion and the production of hydrogen without CO 2 emissions.

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Solid-state physics research has long employed radioactive isotopes to investigate the crystallographic, electric and magnetic properties of nanostructures. Ion implantation (1–100 keV) is the method of choice for incorporating radioactive nuclei into the crystal structure. However, the enormous scientific interest in 2D materials, multiferroics and their interfaces of the last decades has lead to more stringent demands for isotope incorporation. Ultra-low energy (ULE) ion implantation (10–100 eV) provides the ability to precisely tune the depth of the implanted radioactive probes, even in the case of atomically thin 2D materials. To unlock this potential and expand the experimental capabilities of the ISOLDE collaboration in CERN, the apparatus for surface physics and interfaces at CERN (ASPIC), an experienced ultra-high vacuum chamber dedicated to surface characterization and modification, is refurbished and upgraded with a new component: the ASPIC’s ion implantation (ASCII) chamber, designed for ULE ion implantation of radioactive probes. This paper describes the scientific context, design and application of these vacuum chambers.