Dehydrogenation of oligo-phenylenes on gold surfaces

Adsorption of oligo-phenylenes (p-quaterphenyl (p-4P), p-sexiphenyl (p-6P)) on various gold surfaces has been investigated under ultrahigh vacuum conditions. X-ray photoelectron spectroscopy (XPS), low energy electron diffraction (LEED) and thermal desorption spectroscopy (TDS) have been applied to study the adsorbates. We have focused on the dehydrogenation of the organic molecules during thermal desorption. Whereas p-4P exhibits only a small tendency to dehydrogenate on the flat Au(1 1 1) surface, the degree of dehydrogenation on a stepped Au(4 3 3) surface or on a polycrystalline Au surface is considerable. Interestingly, p-6P shows already a strong dehydrogenation even on the flat Au(1 1 1) surface. Dehydrogenation takes place in two successive steps. The first partial dehydrogenation appears at the trailing edge of the oligo-phenyl desorption spectrum. Parallel to that stable polycyclic aromatic hydrocarbons (PAH) are formed on the surface, which eventually dehydrogenate completely at higher temperatures around 850 K. Pure carbon remains on the surface in form of a graphite like layer.