Zeitschriftenaufsätze

Optical microdisk cavities with certain asymmetric shapes are known to possess unidirectional far-field emission properties. Here, we investigate arrays of these dielectric microresonators with respect to their emission properties resulting from the coherent behavior of the coupled constituents. This approach is inspired by electronic mesoscopic physics where the additional interference effects are known to enhance the properties of the individual system. As an example, we study the linear arrangement of nominally identical Lima¸con-shaped cavities and find mostly an increase of the portion of directional emitted light while its angular spread is largely diminished from 20 deg for the single cavity to about 3 deg for a linear array of 10 Lima¸con resonators, in fair agreement with a simple array model. Moreover, by varying the intercavity distance, we observe windows of reversion of the emission directionality and superdirectionality that can be interesting for applications like optical sensing or interconnects. We introduce a generalized array factor model that takes the coupling into account.

Room temperature scanning tunneling microscopy was used to investigate the adsorption of a dye molecule, iron-phthalocyanine (FePc), on ZnO(0001). Submolecular resolution reveals the orientation of molecules with respect to crystallographic directions of the surface. Upon adsorption, the molecular symmetry is reduced. First-principles calculations trace these observations to a strong molecule-substrate bond, which induces deformations of the molecule.