A TPD-based determination of the graphite interlayer cohesion energy

Abstract

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.

Influence of Dispersion Interactions on the Thermal Desorption of Nonplanar Polycyclic Aromatic Hydrocarbons on HOPG

“…This means that the almost perpendicular phenyl rings give rise to a measurable lateral binding energy. Interestingly, the multilayer signal sets in at an unusually high ion dose (four times higher than found previously for the planar PAH homologue hexabenzocoronene C 42 H 18 ). This might be an indicator that, for higher submonolayer coverages, the structure of the rubrene film changes similar to what is seen for pentacene where a planar to tilted herringbone packing transition has been discussed .…”

“…Here, E RS is the rubrene‐substrate binding energy, E RR is the mean lateral rubrene–rubrene binding energy per neighboring molecule, and z is the lateral coordination number. Based on the fact that all previously investigated PAHs have shown the first‐order desorption behavior and taking into consideration that the shape of the TPD spectra shown here does not deviate dramatically from these previous PAH studies, we also assume the first‐order desorption behavior for rubrene. According to STM investigations of rubrene films on graphite, it has six neighbors in a saturated monolayer.…”

“…Table summarizes the corresponding desorption parameters of four different species: the fully planar PAHs C 60 H 22 (indexed HTC in ref. [2]) and C 60 H 24 (TRC) studied by us previously, the “winged” FPC investigated here and buckminsterfullerene C 60 .…”

“…The scaling of physisorption energies with size for homologous series of organic molecules on well‐defined surfaces is of increasing interest toward benchmarking theoretical descriptions of dispersion interactions (and their dependence on localization and transfer of charge) . Recently, we have applied temperature‐programmed desorption (TPD) spectroscopy to determine the desorption energies of a range of large flat polycyclic aromatic hydrocarbons (PAHs) on graphite and have used these values to provide a more accurate estimation of the graphite interlayer cohesion energy by extrapolation . We found that the desorption energies were not measurably influenced by lateral interactions between the fully planar PAHs, despite the fact that theoretical calculations predicted a significant contribution of such interactions to the overall binding energies.…”

“…Both FPC and rubrene were adsorbed onto HOPG (SPI supplies, SPI‐2 and TipsNano, ZYB) using the low energy ion beam deposition setup described in our previous study . Parent cations were generated by electron impact ionization of the corresponding sublimed neutral species.…”