Intramolecular Force Contrast and Dynamic Current-Distance Measurements at Room Temperature.

Scanning probe microscopy can be used to probe the internal atomic structure of flat organic molecules. This technique requires an unreactive tip and has, until now, been demonstrated only at liquid helium and liquid nitrogen temperatures. We demonstrate intramolecular and intermolecular force contrast at room temperature on PTCDA molecules adsorbed on a Ag/Si(111)-(√[3]×√[3]) surface. The oscillating force sensor allows us to dynamically measure the vertical decay constant of the tunneling current. The precision of this method is increased by quantifying the transimpedance of the current to voltage converter and accounting for the tip oscillation. This measurement yields a clear contrast between neighboring molecules, which we attribute to the different charge states.

Structure formation in diindenoperylene thin films on copper(111).

First-principles calculations were combined with scanning tunneling microscopy (STM) measurements to analyze the adsorption of diindenoperylene (DIP) molecules on Cu(111) surfaces. The influence of the substrate on the geometry of single adsorbed molecules, their diffusion barriers, as well as the role of step-edges and intermolecular interactions for molecular self-assembly and structure growth are studied. Long-range ordered arrangements of DIP molecules are found to be most favorable irrespective of the terrace width. Energetically less favored short-range order structures, however, are observed as well.