Due to enormous advances in scanning probe microscopy, it has been possible for a few years to visualize the chemical structure of single organic molecules and intermolecular bonds on surfaces. Such high-resolution imaging, also called 'chemical bond imaging', can be performed with atomic force microscopes (AFM) only at low temperatures (5 K) in ultra-high vacuum. The key to the sensitivity of the chemical bond visualization method lies in the functionalization of the probe tips with a single CO molecule.
Scientific Goals
In this project area, the experimental basis for imaging and spectroscopic analysis of surface-supported molecular reaction steps will be expanded and extended. The imaging technique used is the high-resolution "chemical bond imaging" method, which is based on the non-contact AFM technique (ncAFM) with CO-functionalized tip. Spectroscopic techniques used are TPD, XPS, UPS and NEXAFS. The AFM analyses available in subproject A and those to be newly developed will to a large extent be made available to the other subprojects, giving this subproject a fundamental and unifying character.
Two scientific goals are to be achieved in this subproject: First, the "chemical bond imaging" method will be further developed with respect to the reduction of artifacts caused by the flexibility of the CO molecule at the probe tip. In addition, strategies will be developed to measure three-dimensional molecular structures, because the current technique only allows the imaging of flat, two-dimensional molecules.
Second, model reactions will be used to compare the results of local scanning probe methods with spectroscopic methods. This involves adsorption energies of the molecules (distinguishing between physisorption and chemisorption), which ultimately reflects the influence of the substrate on the (electronic) properties of the reactants and products.
Such complementary analytical techniques, combining structural information on a single-molecule basis with ensemble-based information, will be explored in depth here.
