Surface and quantum-well electronic states in ultra-thin Ir and Pt films on the Au(111) surface

Abstract

Resumen del póster presentado al Symposium on Surface Science (3S), celebrado en St. Christoph am Arlberg (Austria) del 25 de febrero al 10 de marzo de 2018.The heterostructures consisting of the noble metal substrates and the late d-metal adsorbates and other heavy atoms with the degree of coverage from one atom to several monolayers (MLs), have been actively studied for the last two decades. The interest to these systems can be explained by the possibility of exploiting them in chemical industry, namely, in heterogeneous catalysis. It is known that the properties of two-dimensional systems can drastically differ from the properties of their bulk counterparts. Moreover, frequently the degree of coverage plays a crucial role in these effects. An example of such situation is the Pt/Au(111) heterostructure with the Pt adsorbate thickness varying from one to several atomic layers. In general, favorable catalytic activity, resulting in strong enhancement in rates of certain oxidation reactions, of thin Pt films deposited on Au has been found. All of this is making this and similar systems very attractive for experimental and theoretical research. On the other hand, heterostructures containing as a substrate a heavy metal and several atoms/monolayers of metallic adsorbate demonstrate unique properties caused by spin-orbit interaction that may be attractive for spintronics, a research field experiencing nowadays explosive development. A well-known example is the Bychkov-Rashba splitting effect consisting in lifting of a spin degeneration in two-dimensional systems due to spin-orbit interaction. Large Bychkov-Rashba splitting is characteristic for surface states of both noble and late d metals such as Ir and Pt metals. Moreover the heterostructures based on light noble metals (Cu and Ag) and heavy metal adsorbate such as Bi and Pb have a giant spin-orbit splitting of surface states noticeably larger than in pristine materials. The main reason for this giant splitting is the occurrence of a local potential gradient at the surface of such heterostructures that does not exist inside the bulk materials with inversion symmetry. In this work we investigate the formation of the surface and quantum-well states in thin Ir and Pt films deposited on the Au(111) substrate. From comparison of the electronic structure of Ir(111), Pt(111), and Au(111) surfaces one can observe a strong mismatch between positions of the band gaps in the projected bulk electronic structures of these materials. As a result, the electrons related to iridium or platinum atoms are reflected from the gold substrate by its energy gaps. Together with scattering produced by the potential barrier from the vacuum side this introduces the necessary conditions for realization of the quantum-well states. Since the electronic states in Ir and Pt in the Fermi level vicinity are mainly of the d character they present strong localization at the surface. In turn, this produces strong modification in the density of states in the surface region. Studying Ir- and Pt-derived surface and quantum-well states at different regions of the surface Brillouin zone (SBZ) we find distinct formation character. We also investigate in these heterostructures the effect of spin-orbit interaction on the electronic states localized at the surface since despite many experimental and theoretical studies devoted to these systems with adsorbate thickness of several monolayers, the effect of the spin-orbit interaction on the electronic structure of these systems was not addressed.Peer reviewe