Electron dynamics of tip-tunable oxygen species on TiO2 surface

Yuuki Adachi,Masato Miyazaki,Ivan Štich,Hongqian Sang,Yanjun Li,Sourbh Thakur,Lev Kantorovich,Quanzhen Zhang,Ján Brndiar,Yasuhiro Sugawara,Huan Fei Wen

doi:10.1038/s43246-021-00176-5

Abstract

The redox states of oxygen species on the surface of TiO2 can be altered by electron tunneling by varying the applied bias voltage of an atomic force microscope tip. However, tunneling is stochastic in nature and typically requires ultra-low temperatures to obtain statistically significant data. Here, we use a highly sensitive fast atomic force microscopy setup to study redox transitions of oxygen atoms on a TiO2 surface, in the form of reactive oxygen species and single-atom quantum dots, at 78 K. The fast and highly sensitive nature of our experimental setup enables a statistically necessary amount of data to be collected without having to resort to ultra-low temperatures. This enabled us to study multiple dots and provide insight into the electronic structure and correlation between the oxygen species, which are inaccessible by standard atomic force microscopy. We show that single-atom quantum dots exist in two charge states with drastically different conductance, with one being conducting and the other non-conducting.

Highlights

The redox states of oxygen species on the surface of TiO2 can be altered by electron tunneling by varying the applied bias voltage of an atomic force microscope tip
The tunnelling processes are stochastic in nature and collecting sufficient statistics has so far been only possible at ultralow temperatures, when the atomic force microscope (AFM)/scanning tunnelling microscope (STM) system remains stable for sufficient time[20,21,22,23,24]
We show that oxygen species of the same charge that appear identical in AFM imaging are clearly distinguished by our method; this effect is attributed to environmental effects which subtly change their electronic structure

Summary

Introduction

The redox states of oxygen species on the surface of TiO2 can be altered by electron tunneling by varying the applied bias voltage of an atomic force microscope tip. Tuning of the redox states of ROS and SaQDs, preferably not at too low a temperature, can be provided by applying an appropriate bias voltage that facilitates an electron tunnelling between the oxygen atom and the tip of an atomic force microscope (AFM) or scanning tunnelling microscope (STM).

Results

Conclusion