NC-AFM imaging of the TiO(2)(110)-(1 x 1) surface at low temperature.

The TiO(2)(110)-(1 x 1) surface is investigated using non-contact atomic force microscopy (nc-AFM) at 80 K. We successfully obtained a distinct type of image contrast mode which does not exhibit hydroxyl (OH) impurity defects that mostly appear in common nc-AFM images. We named the obtained distinct type of image contrast as the 'hidden mode'. The assignments of surface atomic rows in this contrast mode are not easy in the absence of defects. By recording different contrast modes in the same region of the surface, we identified the atomic rows obtained in the 'hidden mode' image contrast as bridging oxygen atoms (O(b)). The mechanism of contrast formation was attributed to tip-induced displacement of H atoms over oxygen atoms in the OH groups on the O(b) rows. This interpretation was supported by dissipation measurements. A possible candidate for the tip-generating hidden-mode image contrast was interpreted to be a positively terminated tip apex with a dimer-like structure, revealing an attractive interaction with oxygen and a repulsive force on H atom sites. In addition, with a different tip state at close tip-sample distances, we were able to successfully resolve a high resolution image of the in-plane oxygen atoms.