Creation of single oxygen vacancy on titanium dioxide surface
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Maki Kawaib) Department of Advanced Materials Science, University of Tokyo, Kashiwa-shi 277-8561, Japan
Yousoo Kimc) Surface and Interface Laboratory, RIKEN Advanced Science Institute, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan (Received 15 February 2012; accepted 23 April 2012)
Physical and chemical properties of solid materials are modified by introducing defects, which disarrange the atomic periodic structure. Typical example is oxygen vacancies on titanium dioxide (TiO2) surfaces. Oxygen vacancies on TiO2 surfaces provide new physical and chemical surface properties, such as conductivity, catalytic activity, hydrophilicity, etc. To date, annealing, electron-/photo-stimulated desorption, and chemical reaction have been reported to create oxygen vacancies on TiO2 surfaces. However, these techniques do not allow position control of the defects at the atomic scale. We report the creation of single oxygen vacancy using a scanning tunneling microscope (STM). This technique creates oxygen vacancy at desired site. In addition, based on the experimental findings, we discuss the mechanism of manipulating atomic defects using the STM. I. INTRODUCTION
II. EXPERIMENTAL
Titanium dioxide (TiO2) has long been paid attention to because of its potential for many important applications such as catalysts, photocatalysts, sensors, and light-switchable amphiphilic films.1–6 The physical and chemical properties of TiO2 are strongly affected by the existence of atomic defects such as oxygen vacancies, hydroxyls, and Ti interstitials in its crystal structure.1–23 Furthermore, controlling the position of atomic defects in the structure is critical in manipulating the properties of TiO2. The creation of atomic defects on the TiO2 surface has been achieved by annealing,1–6,24 electron-/photo-stimulated desorption,1,25 and reactions with hydrogen sources (atomic hydrogen or water).3–5,16,26–28 These techniques are able to control the atomic defects only at the macroscale. A scanning tunneling microscope (STM) has been used for inducing atomic scale diffusion2,29 and desorption14,22,26,27,30 of the defects. However, the creation of oxygen vacancies via STM, the most typical defect on TiO2 at the atomic scale, has not been achieved so far. Here, we report the creation of single oxygen vacancies at desired sites on the TiO2 surface using STM. In addition, based on the experimental data, we discuss the manipulation of atomic defects on the TiO2 surface using STM.
All experiments were performed in ultrahigh vacuum at 78 K under conditions that permitted unequivocal identification of each defect. STM experiments were performed using a Low temperature scanning tunneling microscope/ scanning tunneling spectroscopy (LT-STM/STS) system (Omicron GmbH, Erlangen, Germany) consisting of two chambers separated by a gate valve. TiO2(110) single crystals (Furuuchi Chem. Co. Ltd., Tsukuba, Japan) were cleaned in the preparation chamber with base pressure of 8 10 8 Pa by cycles of Ar1 sputtering (3 – 5 keV) and annealing at 900–1000 K. After the surface
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