Veranstaltungsdetails

19.5.2015, 17:00
Jungiusstr. 11, Hörsaal AP

SFB 668 - Kolloquium

A. Shluger (University College, London):

Adsorption and organisation of organic molecules at insulating surfaces as imaged by Atomic Force Microscopy

Adsorption and organisation of organic molecules at insulating surfaces as imaged by Atomic Force Microscopy Alexander Shluger Department of Physics and Astronomy, University College London, UK Non-contact atomic force microscopy (NC-AFM) enables imaging of single molecules, clusters, and self-assembled monolayers on insulators at atomic level. Understanding these images requires modelling of adsorption and self-assembly as well as an accurate representation of the tip-sample forces. I will discuss how this is achieved by combining ab initio calculations of adsorption of individual molecules with molecular dynamics study of nucleation and growth of functionalized molecules into ordered monolayers. I will focus mainly on modeling the self-assembly of two organic molecules, 1,3,5-tri-(4-cyano-4,4 biphenyl)-benzene (TCB) and 1,4-bis(cyanophenyl)-2,5-bis(decyloxy)benzene (CDB), on KCl (001), which have been imaged using NC-AFM. Density functional theory (DFT) calculations were used to study the properties of single molecules on the surface. A classical force field was then parameterized using genetic algorithms (GA) for each molecule to mimic the atomic interactions obtained from DFT. Potential of mean force calculations were performed to shed light on molecular desorption rates and the free energy profile of desorption. We then study how molecules interact with each other and with step edges on the KCl (001) surface and find low energy monolayer structures. The stability of these monolayer structures was investigated at varying temperatures. The tip-surface interaction is approximated by a point dipole model. Virtual AFM technique is used to simulate theoretical images that are directly compared to experimental data.