Probing Structure of Cross-Linked (1 × 2) Rutile TiO₂(110): Adsorption of Trimethyl Acetic Acid

Cross-linked (1 × 2) rutile TiO 2 (110) has been extensively studied, yet the exact atomistic model remains a point of contention. Employing a carboxylic acid as a probing molecule, we studied the structure of cross-linked (1 × 2) TiO 2 (110) through the interaction of trimethyl acetic acid (TMAA) with various sites on the surfaces using in situ scanning tunneling microscopy (STM). The comparison of the same area before and after various exposures to TMAA reveals three distinctive adsorption sites: in trough between two adjacent strands, on cross-link, and strand. Trough and cross-link are more preferable adsorption sites than strand. Unlike the surface of (1 × 1) TiO 2 (110) where TMAA dissociates and deprotonated trimethyl acetate (TMA) is strongly chemisorbed, TMAA diffuses along troughs on (1 × 2) reconstructed TiO 2 (110) at low coverages suggesting that TMAA adsorbs molecularly in troughs. At higher coverages, additional TMAA molecules adsorb on strands in both centered and off-centered configurations. We compared three specific atomistic models for (1 × 2) reconstructed TiO 2 (110), Ti 2 O 3, Ti 2 O, and Ti 3 O 6 . The adsorption of TMAA on strands at room temperature strongly supports the Ti 2 O model for cross-linked (1 × 2) reconstructed TiO 2 (110).