Vacuum vapour deposition of phenylphosphonic acid on amorphous alumina

A study of the growth of phenylphosphonic acid (PPOA) on amorphous alumina thin films on top of polycrystalline aluminium foil is presented. The self-assembled monolayer (SAM) of the acid was grown in ultra high vacuum via vapour phase deposition, which allows us to investigate the molecular growth process in situ by photoelectron spectroscopy. The acid adlayer was deposited on the alumina surface at 300 K from an evaporator consisting of a ceramic tube heated by a tungsten wire. On adsorption of the PPOA acid on the alumina surface the anchoring properties of the phosphonic group lead to the formation of an ordered layer with an outward phenyl ring group and a phosphonate interface. The C 1s, P 2s, P 2p, Al 2p and O 1s core level spectra were analysed as a function of the deposition time. The acid adsorption occurs in two ranges: formation of an initial monolayer phase, followed by saturation coverage where the P 2s peak intensity is constant with deposition time. It was confirmed that the phenylphosphonic acid molecules react with the alumina surface forming P–O–Al bonds. It was shown that the SAM formation is driven by the evolution of acid molecular coverage on the alumina surface. The results on the vapour deposited PPOA SAM monolayer on the amorphous alumina surface are consistent with previous findings for a number of phosphonic acids SAMs prepared through immersion of the alumina surfaces in an acid solution.