Daniel Krüger

Interaction of short-chain alkane thiols and thiolates with small gold clusters: Adsorption structures and energetics

Gold–sulfur bonding is investigated theoretically using a variety of electronic structure methods, including the Becke–Perdew semilocal density functional, the B3LYP hybrid approach, the Hartree–Fock method, and the post Hartree–Fock approaches MP2 and QCISD(T). Particular emphasis is given to adsorption structure and energetics in the case of weak and strong interactions of this general type, using up to five gold atoms and up to three carbon atoms in the aliphatic chain. It is found that all methods which take into account electron correlation, including the density functional methods, lead to quite similar structures. Concerning the energetics, the Becke–Perdew functional is found to overbind typically by about 5–15%. Quasiglobal structural relaxation based on ab initio simulated annealing clearly shows that the adsorption of thiolates onto gold clusters results in a dramatic distortion of the cluster framework. From a structural point of view the thiolate sulfur–gold bond has a distinctive directional...

Basic properties of dynamic force spectroscopy with the scanning force microscope in experiment and simulation

Abstract Cantilever dynamics characterizing the operation of a scanning force microscope (SFM) in the dynamic mode at high oscillation amplitudes were investigated in experiment and computer simulation. Measuring the oscillation amplitude of the probing tip and the phase-shift between the driving force and the cantilever response as a function of the tip—sample distance allows us to analyse the dynamic interaction of the SFM tip with the sample surface. We call this process dynamic force spectroscopy (DFS). Computer simulations were applied to analyse discontinuities observed in experimental DFS curves. The investigations show that a sudden change in the amplitude signal and even more pronounced in the phase signal on approaching the tip is related to the transition from a non-contact oscillation (pure attractive interaction) to the tapping mode (attractive as well as repulsive interaction).

Car-Parrinello Density Functional Calculations of the Bond Rupture Process of Thiolate on Gold in AFM Measurements: Progress and First Results

Recently, direct measurements of the forces related to the rupture of a single thiolate-gold bond have been reported [1]. However, the mechanism of the rupture process itself remains unclear. A special interest is focused on the question whether the bond rupture is taking place at the gold-thiolate interface or if gold itself is extracted from the surface during the rupture of of the bond.