We have studied the oxidation of multilayer thin films of coronene (C 24 H 12 ) on graphite under UHV conditions. Coronene films were grown by low-energy cluster ion beam deposition (LECBD, C 24 H 12 + , E kin < 6 eV) and subsequently oxidized by exposing them to a beam of nearthermal atomic oxygen at room temperature. Mass spectra recorded during sublimation of the oxidized coronene films reveal a distribution of emitted species, C 24 H 12 O n (n ≤ 7), which we assign as coronene epoxides. From the fragmentation pattern we infer that primarily rim epoxides are formed, which exhibit a higher stability than core epoxides according to DFT calculations. In addition to epoxides, XPS indicates that other oxidic functional groups, such as ethers, are also formed in smaller relative amounts as nonsublimable species. The overall yield for the thermal desorption of intact coronene oxides can be up to 7% of the deposited coronene, sufficiently high such that this procedure could be useful as a source of monodispersed nanoscale graphene oxides (nano-GOs) for applications in nanotechnology.

Providing a quantitative understanding of the thermodynamics involved in molecular adsorption and self-assembly at a nanostructured carbon material is of fundamental importance and finds outstanding applications in the graphene era. Here, we study the effect of edge perchlorination of coronene, which is a prototypical polyaromatic hydrocarbon, on the binding affinity for the basal planes of graphite. First, by comparing the desorption barrier of hydrogenated versus perchlorinated coronene measured by temperature-programmed desorption, we quantify the enhancement of the strength of physisorption at the single-molecule level though chlorine substitution. Then, by a thermodynamic analysis of the corresponding monolayers based on force-field calculations and statistical mechanics, we show that perchlorination decreases the free energy of self-assembly, not only enthalpically (by enhancing the strength of surface binding), but also entropically (by decreasing the surface concentration). The functional advantage of a chemically modulated 2D self-assembly is demonstrated in the context of the molecule-assisted liquid-phase exfoliation of graphite into graphene.

Temperature Programmed Desorption (TPD) spectroscopy was used to determine the binding energies of polycyclic aromatic hydrocarbons CnHm (22 ≤ n ≤ 60) with highly oriented pyrolytic graphite. These energies were then used to estimate the dispersive graphite interlayer cohesion by means of a refined extrapolation method proposed by Björk et al. This yields a cohesion energy of 44.0 ± 3.8 meV per carbon atom. We discuss some limits of the TPD-based approach and contrast our values with previous determinations of the interlayer cohesion energy of graphite.

A combination of low energy ion beam deposition and mass resolved thermal desorption spectroscopy is applied to analyze the binding behavior of two nonplanar polycyclic aromatic hydrocarbons (PAHs) to highly oriented pyrolytic graphite (HOPG) surfaces—also concerning their lateral dispersion interactions. In particular, the fullerene precursor C60H30 (FPC) and rubrene C42H28 are studied. Due to their smaller contact areas, both molecules exhibit significantly weaker binding energies to the HOPG surface compared to planar PAHs of similar size: C60H30 is bound to the surface by 3.04 eV, which is 0.6 eV lower than for a fully planar homologue. For rubrene, an isolated molecule–substrate binding energy of 1.59 eV is found, which is about 1 eV less than that of the corresponding planar homologue hexabenzocoronene C42H18. In contrast to FPC, rubrene shows a significant (intermolecular) lateral dispersion contribution to the binding energy as the submonolayer coverage increases.

Thin Coronene films on HOPG were oxidized by exposing them to atomic oxygen under ultra-high vacuum conditions. The products were probed by mass-resolved thermal desorption spectroscopy and X-ray photoelectron spectroscopy. The species subliming from thick oxidized films comprise predominantly epoxides C24H12O n (n ≤ 7), and the oxidation of monolayers yields different sublimable products, notably lactones and dilactonesthus providing clear evidence for a surface-mediated reaction mechanism. After on-top oxidation, roughly 7% of the Coronene monolayer can be sublimed as oxidized derivatives (limited by competing surface reactions, which lead to nondesorbable products). The desorption yield can be raised to 10% by depositing the Coronene monolayer onto preoxidized HOPG. On the basis of our observations and literature results concerning HOPG oxidation, we argue that lactones and dilactones can be generated by the reaction of Coronene adsorbates with epoxy and ether species formed on the graphite support. Our results obtained for the O/Coronene/HOPG model system may be relevant for the mechanism of carbon-based oxidation catalysis in general.