Seminars Archive

Molecular self-assembly studied with scanning probe techniques

Abstract
Molecular self-assembly on surfaces constitutes a promising route for creating novel materials and nanodevices in molecular electronics, optoelectronics and biosensing. Self-assembly is governed by forces acting between individual molecules as well as molecules and the substrate. As an example, scanning tunnelling microscopy (STM) images of the temperature-dependent adsorption structures of the amino acid cysteine (HS-CH2-CH(NH2)-COOH) on both Au(110)-(1x2) as well as Au(111) will be presented and discussed in terms of molecule-molecule and molecule-substrate interactions.1-4 Among the naturally occurring amino acids, only cysteine contains a mercapto group (HS-), making this molecule interesting for studying adsorption onto gold surfaces, as the sulphur atom of the mercapto group is known to bind strongly to gold surfaces. Furthermore, cysteine is a chiral molecule, allowing for investigation of chiral effects at the molecular level. STM experiments are limited to conducting surfaces. For a highly resolved study of molecules on insulating substrates, the use of a dynamic scanning force microscope (SFM) is mandatory. Moreover, SFM allows for directly measuring and controlling forces in the range of Pico-Newtons and below. We aim at measuring and controlling forces acting during molecular movement on dielectric surfaces (halides, oxides and others) to both unravel the mechanisms behind self-assembly and to understand and develop molecular manipulation. An outlook will be given illustrating the basic ideas of our future plans. [1] A. Kühnle, T. R. Linderoth, B. Hammer, F. Besenbacher, Nature 415 (2002) 891 [2] A. Kühnle, L. M. Molina, T. R. Linderoth, B. Hammer, F. Besenbacher, Phys. Rev. Lett. 93 (2004) 086101. [3] A. Kühnle, T. Linderoth, F. Besenbacher, J. Am. Chem. Soc. 125 (2003) 14680. [4] A. Kühnle, T. Linderoth, M. Schunack, F. Besenbacher, Langmuir 22 (2006) 2156.