XPS study of the assembling morphology of 3-hydroxy-3-phosphono-butiric acid tert-butyl ester on variously pretreated Al surfaces

X-ray Photoelectron Spectroscopy (XPS) was used to study the deposition morphology of 3-hydroxy-3-phosphono-butiric acid tert  -butyl ester on aluminium oxide. The deposition was investigated in connection with the acid–base properties of the oxide surface as defined by its hydroxyl concentration. Various pretreatments were applied on pure aluminium, and the XPS analysis showed that the hydroxyl content depended significantly on the pretreatment procedure. XPS quantitative analysis showed concentrations of the phosphonic acid in the range between 10141014 and 6×10146×1014 molecules/cm2. The compound concentration was found to increase with the rise of the surface hydroxyl fraction. The layer morphology was revealed by showing that the concentration of the organic molecules on the surface was enough to complete a monolayer coverage only and by proving that the organic compound was indeed deposited as a monolayer. The modeling of the XPS data suggested that the thickness of the monolayer was about 3.5 Å.