X-ray reflectivity, cyclic voltammetry, and scanning tunneling microscopy (STM) are used to examine the structure of α-SiW12O44- or silicotungstic acid (STA) adsorbed on Ag(100) in acid solution. The voltammetry shows that STA passivates the Ag surface relative to electron transfer to a solution redox species. STM images reveal the formation of a series of lattice structures, one of which can be associated with a commensurate (√13×√13)R33.69° structural model. X-ray reflectivity measurements show uniquely that STA orients with its four-fold axis perpendicular to the Ag(100) surface and that the center of the STA molecule is 4.90 Å above the top layer of the Ag substrate. Analysis of bond lengths leads to a footprint of STA on Ag(100), in which the four terminal O atoms are located near the hollow sites and have a Ag - O bond length of 2.06 Å. This bond length is consistent with a strong covalent interaction between STA and the Ag surface.
ASJC Scopus subject areas
- Colloid and Surface Chemistry