Adsorption, initial growth and desorption kinetics of p-quaterphenyl on polycrystalline gold surfaces

Thermal desorption spectroscopy (TDS) and X-ray photoelectron spectroscopy (XPS) have been applied to investigate the kinetics of adsorption, layer growth and desorption of p-quaterphenyl (P4P) on polycrystalline gold surfaces. Two different desorption peaks resulting from a monolayer (wetting layer) and a multilayer can be observed. The multilayer predominantly grows in form of a continuous film at 93 K, whereas at room temperature needle-like island growth is observed. A rearrangement (island formation) of the continuous multilayer takes place during heating prior to desorption. The influence of carbon on the adsorption/desorption kinetics of the monolayer has been studied in detail. On the clean surface some amount of adsorbed P4P dissociates and hydrogen is released at about 650 and 820 K, respectively. No dissociation of P4P takes place on the carbon-covered surface. The intact P4P molecules of the monolayer desorb in form of two broad peaks around 420 and 600 K, the multilayer desorbs with zero order above 350 K. Quantitative measurements with a quartz microbalance yield a mean thickness of 0.27 nm for the monolayer, suggesting that the P4P molecules are lying flat on the surface, for both the clean and the carbon-covered surface.