Based on first-principles calculations, we propose an exchange-transfer mechanism to understand the distinctively different behaviors of Pd and Pt contacts on graphene. The feature of the mechanism is that the pi electrons on the graphene transferring to the Pd d_{xz} + d_{yz} orbital are largely compensated by the electrons from the Pd d_{z;{2}} orbital. This mechanism causes more interaction states and transmission channels between the Pd and graphene. Most importantly, the mechanism keeps enough pi electrons on the graphene. We show that a tensile strain in the Pd layer, necessary to match the graphene lattice, plays a key role in stimulating this exchange transfer when Pd covers on graphene, while a similar strain in the Pt layer does not cause such a mechanism.

The geometric and electronic structures of a monolayer of C 60 on a h-BN monolayer-covered Ni͑111͒ surface are studied by first-principles calculations. The interaction between ions and electrons is described by the projector-augmented plane-wave method. The most stable structure of the h-BN/Ni͑111͒ surface is found to be N on the top and B on the fcc site of Ni͑111͒. Upon adsorption, the structure in which a hexagon of the C 60 molecular is parallel to the substrate is 0.1 eV more favorable in energy than that of a pentagon parallel to the substrate. For the most stable adsorption sites of C 60 on h-BN/Ni͑111͒, the distance between the bottom hexagon of C 60 and the h-BN / Ni substrate is 3.6 Å. The calculated results show that the energy differences among different orientations are all smaller than 0.22 eV. No magnetic moment is found for the C 60 monolayer. The calculated electronic structures confirm that the h-BN/Ni͑111͒ is a good insulator platform to study the electronic structures of C 60 ultrathin films, since only a weak interaction and small charge transfer exist between C 60 and h-BN/Ni͑111͒.

We report a first-principles study of magnetic properties of organic− ferromagnetic interfaces between photoswitchable azobenzene molecules and Fe/ W(110) surfaces. Our calculations demonstrate that the magnetic properties of the hybrid interface, such as the local magnetic moment and spin polarization, change significantly as the azobenzene molecule switches reversibly between the trans to the cis form. The molecule−surface interaction, which determines the feasibility of isomerization of the azobenzene on the surface, can be altered by chemical modification of the molecule. This study suggests a new pathway to manipulate magnetism and spin polarization at organic−ferromagnetic hybrid interfaces.