Combined in situ PM-IRRAS/QCM studies of water adsorption on plasma modified aluminum oxide/aluminum substrates

Abstract

Water adsorption on plasma modified oxyhydroxide covered aluminum surfaces was analyzed by means of a set-up combining in situ photoelastic modulated infrared reflection absorption spectroscopy (PM-IRRAS) and quartz crystal microbalance (QCM) in a low-temperature plasma cell. The chemical structure of the surface before and after the plasma treatment was moreover characterized by means of X-ray photoelectron spectroscopy (XPS) analysis.The surface chemistry of oxide covered aluminum was modified by oxidative and reductive low-temperature plasma pre-treatments. The Ar-plasma treatment reduced the surface hydroxyl density and effectively removed adsorbed organic contaminations. Surface modification by means of a water plasma treatment led to an increased surface hydroxyl density as well as an increase of the thickness of the native oxide film. The adsorption of water at atmospheric pressures on plasma modified aluminum surfaces led to a superimposition of reversible water layer adsorption and a simultaneous increase of the oxyhydroxide film thickness as a result of a chemisorption process.The amount of physisorbed water increased with the surface hydroxyl density whereas the chemisorption process was most significant for the surface after Ar-plasma treatment and almost negligible for the already water plasma treated surface.