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MI: Fachverband Mikrosonden

MI 10: Scanning Probe Microscopy

MI 10.4: Vortrag

Donnerstag, 14. März 2013, 10:30–10:45, H5

Kelvin Probe Force Microscopy in Liquids — Anna Domanski, Esha Sengupta, Karin Bley, Stefan Weber, Maria Untch, Clemens Weiss, Katharina Landfester, Hans-Jürgen Butt, and •Rüdiger Berger — Max-Planck-Institut für Polymerforschung, Mainz, Ackermannweg 10, Germany

Thin organic films on metal surfaces lead to a significant shift in the electronic work function Φ of the metals. Typically ultraviolet photoelectron spectroscopy (UPS) is used to determine work functions of materials. UPS measurements require areas > 1 mm² and thus, variations on a nanometer scale cannot be investigated directly. Kelvin Probe Force Microscopy (KPFM) is a powerful tool to investigate local surface potential changes with high spatial resolution. Often ultra-high vacuum conditions are required to keep surfaces clean. Here, we will discuss KPFM measurements in unipolar liquids and present an in-situ study of the self-assembly process of hexadecanethiols on gold in decane (1). As test structures, we prepared nanostructured Au surfaces by colloid monolayer lithography. Our study revealed a work function shift for hexadecanethiols on Au by -1.5 eV which is in excellent agreement with UPS data. The lowering of the work function is induced by the formation of an interfacial dipole layer which is directed towards the metal surface, i.e. the negative charges are positioned at the metal/sulfur interface and the positive charges to the decane interface. Our study shows that electrical methods such as KPFM benefit largely by performing measurements in liquids.

(1) A.L. Domanski et al., Langmuir 28 13892-13899 (2012)