Bonding of Methyl Phosphonate to TiO2(110)

We have used scanning tunneling microscopy (STM), noncontact atomic force microscopy (NC-AFM), low energy electron diffraction (LEED), and ab initio calculations to study adsorbates resulting from exposure of rutile TiO 2 (110)1 × 1 to methyl phosphonic acid (CH 3 P═O(OH) 2 ). At low exposures, adsorbates appear on the 5-fold coordinated Ti (Ti 5c ) rows. As the coverage of adsorbates approaches 0.5 ML, STM images show an ordered 2 × 1 overlayer consistent with LEED. We propose that the phosphonic acid is deprotonated with the resulting phosphonate bridging across two adjacent Ti 5c atoms in the [001] direction. This bridging conformation would lead to the observed 2 × 1 overlayer and is analogous to that found for a range of carboxylates adsorbed on TiO 2 (110).