AVS 59th Annual International Symposium and Exhibition
    Oxide Heterostructures-Interface Form & Function Focus Topic Monday Sessions
       Session OX+SS+TF+MI-MoA

Paper OX+SS+TF+MI-MoA11
In Situ Interface Analysis of Self-Assembled Monolayers on Metal Surfaces at High Water Activities by Means of a PM-IRRAS/QCM-Setup

Monday, October 29, 2012, 5:20 pm, Room 007

Session: Chemistry of Oxide Surfaces and Interfaces
Presenter: I. Giner, University of Paderborn, Germany
Authors: I. Giner, University of Paderborn, Germany
M. Maxisch, University of Paderborn, Germany
G. Grundmeier, University of Paderborn, Germany
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Aluminum and its alloys are widely used as engineering material and in a wide range of applications ranging from the aviation industry to the automotive and construction industries. As almost all engineering metals, aluminum under ambient conditions is covered by a native oxide film which alters significantly its surface physical and chemical properties. For corrosion protection and adhesion promotion, oxide covered aluminum surfaces are coated with organic films. Ultra-thin films or even monomolecular layers of organic acids like self-assembled monolayers (SAMs) of organophosphonic and organocarboxylic acids have been investigated as new advanced interfacial layers for aluminum alloys.1 However, the stability of the self-assembled monolayers under environmental conditions is an aspect for technical applications. Different studies concerning to the stability and structure of the self-assembly monolayers under high humidity’s conditions have been performed.2 These studies revealed that the organic film decreased the amount of interfacial water layer but cannot prevent the water diffusion through the monolayer.3 The aim of the present work is to establish an in-situ setup combining quartz crystal microbalance (QCM) and PM-IRRAS to study the chemistry of passive films and adsorbed organic monolayers at high humidity. The metal coated quartz was used as the reflecting substrate for the PM-IRRAS measurement. Thereby, the structure of the monolayer, the amount of adsorbed water and the chemical state of the surface layer in the presence of an adsorbed water layer could be analysed in-situ. The surface hydroxyl density prior to organic molecule adsorption was adjusted by means of low temperature Ar- and H2O- plasma treatments. Adsorption studies of H2O on nonadecanoic carboxylic acid (NDA) monolayer modified surfaces in comparison to bare oxide covered aluminum surfaces showed, that the NDA monolayer leads to a reduced amount of adsorbed water based on the inability of water to form hydrogen bonds to the low energy aliphatic surface chemistry. Moreover the kinetics of chemisorption of water indicated by the oxyhydroxide peak growth at SAM/metal interfaces could be significantly inhibited. Furthermore, it is noticeable that interfacial carboxylate group coordinatively bound the oxide as well as the orientation of the NDA monolayer is not affected by the adsorption of several monolayers water. Bibliography 1. Thissen, P et al. Langmuir 2010, 26, (1), 156-164 2. Thissen, P et al. Surface & Coatings Technology 2010, 204 (21-22), 3578-3584. 3. Maxisch, M et al. Langmuir 2011,27 (10), 6042-6048