STM visualization of site-specific adsorption of pyridine on TiO2(110)

Pyridine molecules adsorbed on a TiO2(110)-(1 x 1) surface were visualized by scanning tunneling microscopy (STM). Direct evidence of coordination-controlled adsorption on a metal oxide surface is reported for the first time. A pyridine molecule was more strongly adsorbed on a four-fold coordinated Ti atom exposed at single-atom-height step edges than on the five-fold coordinated Ti site over the perfect (110) terrace. Furthermore, the activity of the four-fold coordinated Ti sites at step edges was strongly dependent on the orientation of the step in azimuth. Sequential imaging of the pyridine-exposed surface revealed that terrace-adsorbed molecules were transformed to step-bonded species and vice versa even at room temperature.