Electronic properties and adsorption structures of tetracene on the Ag(110) surface

The adsorption of tetracene on Ag(110) surface has been studied using ultraviolet photoemission spectroscopy (UPS) and first-principles density function theory (DFT) calculation. The five emission features originating from the organic molecules locate at 3.4, 5.7, 6.3, 7.2, and 8.8eV below the Fermi level, respectively. There is no apparent binding energy shift of these features with the increasing coverage of tetracene, indicating a relatively weak interaction between tetracene and the Ag(110) substrate. Moreover, our DFT calculation shows that tetracene molecules prefer to adsorb between two Ag atomic rows of the first layer with its molecular axis along the [001] direction of the substrate, and the center of its second benzene ring locates at top site of Ag atoms of the second layer. With this optimized adsorption configuration, the π–d interactions between tetracene and Ag(110) are maximized. Comparing with the densities of states (DOS) before and after tetracene adsorption, no apparent intensity change can be observed for the DOS from p-orbital of tetracene, suggesting that the coupling between the substrate d-band and the filled p-orbitals of tetracene are relatively weak.