Binding of Single Gold Atoms on Thin MgO(001) Films

Abstract

In the present Letter the first electron paramagnetic resonance spectra of single metal atoms on a single crystalline oxide surface are presented. For Au atoms on a MgO(001) film investigated here an analysis of the angular dependent resonance positions and the hyperfine coupling to (17)O shows that the atoms are bound on top of oxygen ions on the terrace of the film. This result is in perfect agreement with scanning tunneling microscopy measurements at 5 K presented here. The measured hyperfine matrix components allow an experimental verification of the theoretically proposed binding mechanism of Au atoms on MgO. In particular, the large reduction of the isotropic hyperfine coupling constant of supported Au as compared to free atoms is not due to a charge transfer at the interface but a hybridization of orbitals and a resulting polarization of the unpaired electron.

Models in Catalysis

“…By a full analysis of the spectral angular dependence and the additional super-hyperfine interaction with O of an 17 O enriched MgO film, the Au atoms were shown to adsorb on top of oxygen ions in agreement with theoretical predictions [46][47][48]. DFT calculations showed, that these observations are indicative of polarization of the singly occupied 6s orbital of neutral Au atoms away from the MgO surface [40]. Adsorbing probe molecules such as CO onto the Au atoms provide the opportunity to apply IR spectroscopy to this system (Fig.…”

“…6b) and investigated further by electron paramagnetic resonance (EPR) spectroscopy [40]. The latter technique for in situ surface studies has been developed at the Fritz Haber Institute [43][44][45].…”

“…Adsorption on defect-free insulating oxides is generally weak, given the high degree of bond saturation at their surface and the large gap that governs their electronic structure [37][38][39][40][41][42]. Metal atoms deposited onto pristine oxides have essentially two means to interact with the surface.…”

Properties of oxide thin films and their adsorption behavior studied by scanning tunneling microscopy and conductance spectroscopy

“…393 The formation of 2D islands is in sharp contrast to the 3D growth regime that is generally observed for metals on bulk oxides. 37,46,394 It reflects the tendency of Au to maximize the contact area with the oxide film and therewith the number of electrons being transferred into the Au affinity levels. Similar to the mechanism discussed for Au monomers and chains, charged gold islands show an increased adhesion to the oxide surface, resulting from polarization and electrostatic contributions to the total binding energy.…”

Manipulation of the Charge State of Single Au Atoms on Insulating Multilayer Films

“…It might seem natural to employ bulk insulators and bulklike insulating films [1,2] for these purposes, on which charge states are intrinsically stabilized by the suppression of charge transfer with the substrate. However, controlled manipulation of the charge state of single atoms and molecules is hampered by technical issues on these substrates and has yet to be shown.…”