Electronic structure ofMn12derivatives on the clean and functionalized Au surface

Abstract

We present a detailed study on the electronic properties of monolayers of ${\mathrm{Mn}}_{12}$ 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 ${\mathrm{Mn}}_{12}$-clusters were probed by means of x-ray absorption spectroscopy (XAS) and resonant photoelectron spectroscopy (RPES) at the Mn $2p\text{\ensuremath{-}}3d$ absorption edge, respectively. XAS measurements reveal a significant difference between the Mn oxidation states of ${\mathrm{Mn}}_{12}$ cores bound to the Au surface compared with the single crystal environment. Direct deposition of ${\mathrm{Mn}}_{12}$ derivatives onto the Au surface leads to a strong fragmentation of ${\mathrm{Mn}}_{12}$ cores. An appropriate combination of ${\mathrm{Mn}}_{12}$ cluster and substrate functionalization leads to formation of ${\mathrm{Mn}}_{12}$ monolayers with a large fraction of ${\mathrm{Mn}}_{12}$ 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 $\mathrm{LDA}+U$ calculations on ${\mathrm{Mn}}_{12}$ for $U=4\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ [Boukhvalov et al., J. Electron Spectrosc. Relat. Phenom. 137--140, 735 (2004)] was found, showing the importance of electron correlation effects in ${\mathrm{Mn}}_{12}$ systems.