The interlayer cohesive energy of graphite from thermal desorption of polyaromatic hydrocarbons

Renju Zacharia¹, Hendrik Ulbricht¹ and Tobias Hertel^1,2

¹Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin, Germany

²Department of Physics and Astronomy, Vanderbilt University, Nashville, TN, USA (beginning January 2004)

We have studied the interaction of polyaromatic hydrocarbons (PAHs) with the basal plane of graphite using thermal desorption spectroscopy. Desorption kinetics of benzene, naphthalene, coronene and ovalene at sub-monolayer coverages yield activation energies of 0.50 eV, 0.85 eV, 1.40 eV and 2.1 eV, respectively. Benzene and naphthalene follow simple first order desorption kinetics while coronene and ovalene exhibit fractional order kinetics owing to the stability of 2-D adsorbate islands up to the desorption temperature. Pre-exponential frequency factors are found to be in the range 10¹⁴-10²¹s^-1 as obtained from both Falconer-Madix (isothermal desorption) analysis and Antoine's fit to vapour pressure data. The resulting binding energy per carbon atom of the PAH is 52±5 meV and can be identified with the interlayer cohesive energy of graphite. The resulting cleavage energy of graphite is 61±5 meV/atom which is considerably larger than previously reported experimental values.