Yaobiao Xia

Acetone-Assisted Oxygen Vacancy Diffusion on TiO2(110)

We have studied the dynamic relationship between acetone and bridge-bonded oxygen (Ob) vacancy (VO) defect sites on the TiO2(110)-1 × 1 surface using scanning tunneling microscopy (STM) and density function theory (DFT) calculations. We report an adsorbate-assisted VO diffusion mechanism. The STM images taken at 300 K show that acetone preferably adsorbs on the VO site and is mobile. The sequential isothermal STM images directly show that the mobile acetone effectively migrates the position of VO by a combination of two acetone diffusion channels: one is the diffusion along the Ob row and moving as an alkyl group, which heals the initial VO; another is the diffusion from the Ob row to the five-coordinated Ti(4+) row and then moving along the Ti(4+) row as an acetone, which leaves a VO behind. The calculated acetone diffusion barriers for the two channels are comparable and agree with experimental results.

Imaging reactions of acetone with oxygen adatoms on partially oxidized TiO2(110)

Understanding the interaction of O2 with ketones on metal oxide surfaces is important for the photo-oxidation of toxic organic molecules. The consecutive reaction steps of acetone molecules with oxygen adatoms (Oas) on partially oxidized TiO2(110) surfaces have been studied using high-resolution scanning tunneling microscopy (STM) at 300 K. The sequential isothermal STM images reveal two types of acetone-Oa species as a result of reactions of acetone with an oxygen adatom and a bridging bound oxygen vacancy (V(O)). One such species is the Ti5c-bound acetone-Oa diolate formed from Ti5c-bound acetone reacting with Oa. The diolate is mobile at 300 K and can assist the diffusion of surface Oa by exchanging the acetone oxygen with the Oa. The second acetone-Oa species is the V(O)-bound acetone-Oa complex formed from a V(O)-bound acetone reacting with an Oa located on the neighboring Ti row. The V(O)-bound complex is stationary at 300 K. This species has not been reported previously.

Tip-assisted directional growth of atomically thin Ag islands

Abstract The growth and decay of metal nanostructures are important in many areas of physical science and catalytic chemistry. Here, we show the directional growth of Ag island stripes at room temperature via tip-assisted coarsening of hexagonal islands on Ag(111) using scanning tunneling microscope (STM). The mechanism of this process is attributed to the alignment of the adatom and vacancy islands along the scanning direction via tip-sample interaction during the process of the intrinsic decay of the metastable Ag islands. We find that this tip-assisted island growth is not directly related to the tunneling current and the bias voltage. Experiments performed using Ag tips and W tips show similar coarsening effects. The chamber pressure and the O2 exposure also do not have systematic effects on the rate of island growth. The tip-assisted coarsening strongly depends on the tip morphology.