Lithium incorporation into a silica thin film: Scanning tunneling microscopy and density functional theory

Abstract

The interaction of Li with a thin silica film grown on Mo͑112͒ has been studied with low-temperature scanning tunneling microscopy ͑STM͒ and density functional theory ͑DFT͒. Thanks to the porous silica structure, single Li atoms are able to penetrate the oxide layer and bind at the metal-oxide interface. From the distinct topographic signature of the embedded atoms, the interfacial adsorption sites are determined to be along the furrows of the Mo͑112͒ surface. With increasing Li coverage, the formation of an ordered superstructure is observed, where stripes of high and low Li density alternate in the direction perpendicular to the Mo furrows. The ordering effect is explained by the anisotropic screening response of the Mo͑112͒ surface. The Li becomes cationic upon adsorption at the interface and substantially lowers the work function of the silica/Mo system. This work-function decrease is directly deduced from the downshift of the silica conduction band, as determined with STM conductance spectroscopy and DFT calculations. The derived interrelation between work function and Li coverage strongly deviates from the universal behavior found on metal surfaces, reflecting the superior screening of the Li + ions in their binding sites at the metal-oxide interface.

Induced work function changes at Mg-doped MgO/Ag(001) interfaces: Combined Auger electron diffraction and density functional study

“…By varying the kind of interface defects, it is possible to tune the work function of the metal/oxide system in a desired way [13][14][15][16][17] . For examples, recent theoretical studies of doped MgO/Ag(001) interfaces, have shown that manipulating the interface by inserting oxygen or magnesium vacancies and impurities leads to an enhanced chemical reactivity of the oxide surface with respect to the catalytic dissociation of H 2 O 18 , and have further highlighted the influence of interfacial oxygen vacancies and impurities on the MgO/Ag(001) work function 19,20 .…”

Mechanism of Charging of Au Atoms and Nanoclusters on Li Doped SiO2/Mo(112) Films

“…These values are overestimated by about a factor two compared to experiment (for possible explanations see ref. [45]). …”

“…Indeed, STM images show that the Li atoms penetrate below the silica layer and substantially lower the work function of the silica/Mo system. [44,45] The work function decrease predicted by the calculations has been deduced from the down-shift of the silica conduction band, as probed by conductance spectroscopy. [45] The Li-doped silica films have then been used to study the adsorption properties of Au atoms and clusters.…”

“…[44,45] The work function decrease predicted by the calculations has been deduced from the down-shift of the silica conduction band, as probed by conductance spectroscopy. [45] The Li-doped silica films have then been used to study the adsorption properties of Au atoms and clusters. [44] Au atoms were deposited at 20 K from a gold-plated tungsten filament.…”

“…This possibility has been investigated theoretically [43] and proven experimentally. [44,45] Lithium was chosen because it can easily penetrate the rings of the silica film and form stable Li + species at the interface. If the alkali atom would remain adsorbed above the surface, as it is the case for the larger K + ions, these could bind directly to the deposited gold atoms or particles, forming bimetallic clusters, an undesired effect.…”