Electronic structure of Mn12 derivatives on the clean and functionalized Au surface

Abstract

We present a detailed study on the electronic properties of monolayers of Mn12 derivatives chemically grafted on clean as well as on functionalized Au(111) surfaces. Scanning tunneling microscopy and x-ray photoelectron spectroscopy were employed to ensure the successful monolayer deposition. Unoccupied and occupied valence band states in the electronic structure of Mn12-clusters were probed by means of x-ray absorption spectroscopy (XAS) and resonant photoelectron spectroscopy (RPES) at the Mn 2p-3d absorption edge, respectively. XAS measurements reveal a significant difference between the Mn oxidation states of Mn12 cores bound to the Au surface compared with the single crystal environment. Direct deposition of Mn12 derivatives onto the Au surface leads to a strong fragmentation of Mn12 cores. An appropriate combination of Mn12 cluster and substrate functionalization leads to formation of Mn12 monolayers with a large fraction of Mn12 cores retaining their structural integrity upon surface deposition. By extracting the Mn 3d partial density of states from the RPES spectra a very good agreement with previously reported LDA+U calculations on Mn12 for U=4 eV [Boukhvalov et al., J. Electron Spectrosc. Relat. Phenom. 137 140, 735 (2004)] was found, showing the importance of electron correlation effects in Mn12 systems.