The energetic position of the Au(111) Shockley surface state is compared before and after adsorbing different rare gas monolayers (Ar, Kr, and Xe). We used ultraviolet photoelectron spectroscopy (UPS) and scanning tunneling spectroscopy (STS) in combination to get more complete information by using the advantages of both methods. For determining the energetic position and the effective mass of the surface state in UPS an analytic mathematical method is used, which takes the finite angular resolution of the analyzer into account. We performed STS scans for the pure Au(111) surface as well as covered with a monolayer Kr and Xe. For an accurate analysis it is possible to use an extended Kronig-Penney model to take into account the influence of the 23ϫ ͱ 3 reconstruction. We found that the first monolayer of a rare gas induces shifts of around 50-150 meV increasing with the gas atomic number, whereas a second monolayer has only a small influence of about 3-18 meV. Using an image potential model it is possible to characterize these shifts qualitatively. For a semiquantitative analysis the phase accumulation model is applied. Within this model we can describe the experimental data roughly with a Coulomb potential changing in dependence of the electron affinity and the dielectric constant of the rare gas.

P3HT (poly(3-hexylthiophene-2,5-diyl)):PC61BM ([6,6]-phenyl-C61 butyric acid methyl ester) bulk heterojunction solar cells are fabricated and characterized as a function of solar intensity, temperature, and aging at vacuum conditions under illumination with AM0 illumination for testing potential use in space applications. The evolution of the inner film morphology is probed with grazing incidence X-ray scattering techniques and correlated with the evolution of the efficiency during aging. Grazing incidence wide-angle X-ray scattering shows almost no change of the crystalline structure of the P3HT:PCBM films due to aging. In contrast, the morphological evolution on the mesoscale extracted from grazing incidence small-angle X-ray scattering can explain the observed decay of the overall efficiency. The behavior at high solar intensities as well as elevated temperatures suggests that organic solar cells have high potential for space applications in the future.

We have studied the effect of Mg doping on the surface kinetics of GaN during growth by plasma-assisted molecular-beam epitaxy. Mg tends to segregate on the surface of GaN, inhibiting the formation of the self-regulated Ga film which is used as a surfactant for the growth of undoped and Si-doped GaN. The growth window is hence significantly reduced. Higher growth temperatures lead to an enhancement of Mg segregation and an improvement of the surface morphology.