We investigate the atomic and electronic structure of ultra-thin ZnO films (1 to 4 layers) on the (111) surfaces of Ag, Cu, Pd, Pt, Ni, and Rh by means of density-functional theory. The ZnO monolayer is found to adopt an α-BN structure on the metal substrates with coincidence structures in good agreement with experiment. Thicker ZnO layers change into a wurtzite structure. The films exhibit a strong corrugation, which can be smoothed by hydrogen (H) adsorption. An H over-layer with 50% coverage is formed at chemical potentials that range from low to ultra-high vacuum H2 pressures. For the Ag substrate, both α-BN and wurtzite ZnO films are accessible in this pressure range, while for Cu, Pd, Pt, Rh, and Ni wurtzite films are favored. The surface structure and the density of states of these H passivated ZnO thin films agree well with those of the bulk ZnO(0001¯)-2×1-H surface.

We theoretically investigate the optical absorption of a hybrid system consisting of an organic molecular film on top of a semiconductor substrate. The electronic states of the isolated spatially separated constituents couple due to the Coulomb interaction of the optically induced charge carriers across the film-substrate interface. Focussing on the coupling of optical active molecular transitions to semiconductor continuum states, we find that the nonradiative dipole-dipole energy transfer causes the formation of coupled excitations, effectively reducing the excitation energy of the optical resonance in the molecular film and inducing a broadening of the associated absorption peak. In the framework of the Heisenberg equation of motion technique, we derive the Bloch equations for these hybrid systems. The input parameters for our model system of ladder-type quarterphenyl (L4P) molecules on the ZnO(1010) surface are taken from density functional theory calculations.

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