Measurement and Manipulation of the Charge State of an Adsorbed Oxygen Adatom on the Rutile TiO₂(110)-1×1 Surface by nc-AFM and KPFM

Abstract

Oxygen adatom, charge state, noncontact atomic force microscopy (nc-AFM), Kelvin probe force microscopy (KPFM), tipsample distance, tip-induced electric field, density functional theory (DFT).

Elucidating the charge state of an Au nanocluster on the oxidized/reduced rutile TiO2 (110) surface using non-contact atomic force microscopy and Kelvin probe force microscopy

“…The oxygen molecules are known to dissociate and adsorb as O ad on top of these ve-fold coordinated Ti atoms. 28,29 Thus, the bright row and dark row observed in Fig. 1(c) and (d) correspond to the O row and Ti row.…”

“…For details, please refer to our previous works. 28,30 Results and discussion First, the surfaces were proven to be reduced/oxidized TiO 2 (110) surfaces via atomically resolved AFM images. This is important to exclude the possibility of performing experiments on high coverage hydroxyl TiO 2 (110), which would strongly alter the properties of the Au nanoclusters.…”

“…1(d) are O ad . 28,29 In the case of NC-AFM imaging on these surfaces, it is well known that the image contrast strongly depends on the chemical construction of the tip apex. 27 In a recent work, three common contrasts (neutral, hole, and protrusion types) were observed on rutile TiO 2 (110) surfaces; especially, the image obtained by the neutral mode tip is believed to give a contrast resembling the true geometrical structure and provides an easy way to identify the atomic species adsorbed on this surface.…”

“…3(a), because the electronegatively O ad tends to withdraw the electrons from the Au nanocluster, the Au nanocluster becomes positively charged. 28,29 In contrast, O v tends to supply excess electrons to the Au nanocluster, due to which the Au nanocluster becomes negatively charged (Fig. 3(b)).…”

“…To gain more insights into the strong contrast difference observed in the LCPD images, the system was further investigated by performing KPFM measurements as a function of the tip sample distance, ensuring that no changes in the tip or deformation of the Au nanoclusters could occur. 22,25,28,30 The experiment was conducted as follows: the initial positions of the Au nanoclusters on oxide/reduced TiO 2 surfaces were conrmed by AFM imaging. Aer AFM imaging, the tip was brought above the Au nanocluster and KPFM feedback was turned on.…”