Controlling structural, chemical and electronic properties of single molecules on surfaces

With the prospects of realizing electronic circuitry and machinery consisting of a single-molecule, the control of the molecular characteristics down to the atomic level is essential. In this thesis, fundamental investigations of structures, electronic properties and diffusion of molecules on surfaces are presented. The experiments are performed by means of scanning tunneling microscopy (STM) and atomic force microscopy (AFM) at low temperature in ultra-high vacuum. The control of elaborated structures is achieved by studying on-surface chemical reactions and spray-deposited molecules by high-resolution AFM imaging with CO terminated tips. To mimic a p-n junction, a donor-acceptor (DA) molecule on a thin insulating film is probed to disentangle its structure, electronic states and charge redistribution. Interestingly, the DA character of the molecule is altered at specific atomic positions, and thus controlled by inducing a change of the adsorption site by tip manipulation. This consists of an example of a molecular switch. In this line, tip manipulation experiments are pushed forward during the NanoCar Race by steering a single molecule over the surface using tunneling electrons. The results of this thesis demonstrate the impact of the molecular design on electronic and adhesion properties influencing the performance of such molecular systems.