Imaging of individual formate ions adsorbed on TiO2(110) surface by non-contact atomic force microscopy

We have succeeded in imaging individual formate ions adsorbed on TiO2(110)-(1×1) by non-contact atomic force microscopy. Formic acid is dissociatively adsorbed on TiO2(110)-(1×1) surface at room temperature to give formate ions (HCOO−) which order in a (2×1) periodicity at the saturation coverage of 0.5 ML. The (2×1)-formate overlayer was resolved as ordered bright spots with a rectangular unit of 0.65×0.59 nm2. Dispersed formate ions of lower coverages were also observed as bright spots between the bridging oxygen ridges along the [001] direction.