Sasahara Akira, Pang Chi Lun, Onishi Hiroshi
Japan Science and Technology Agency, Kawaguchi, Saitama 332-0012, Japan.
J Phys Chem B. 2006 Jul 13;110(27):13453-7. doi: 10.1021/jp062000c.
Titanium dioxide (TiO2) (110) surfaces with Pt adatoms were examined using a noncontact atomic force microscope (NC-AFM) and a Kelvin probe force microscope (KPFM). Topographic images with NC-AFM identify Pt atoms adsorbed at three different sites. These sites are on the Ti atom rows, on the O atom rows, and in O atom vacancies. Most Pt adatoms were observed on Ti atom rows. Successively recorded images show that the Pt adatoms on Ti atom rows (adatoms A) and O atom rows (adatoms C) are mobile while the adatoms in the O atom vacancies (adatoms B) are not. Adatoms A and adatoms B were identified in KPFM images. However, adatoms C were not visualized in KPFM images because they moved quickly or were swept out by the tip. The KPFM measurements reveal that the work function on adatoms A are lower than that on the surrounding (1 x 1) surface by 0.24 eV whereas adatoms B reduced the work function by 0.26 eV. The work function decrease is interpreted with an electric dipole moment directed toward the vacuum, as a result of electron transfer from the adatoms to the TiO2 substrate. In an O atom vacancy, the adatom B is in contact with two Ti atoms and therefore the electron transfer can be enhanced.
使用非接触原子力显微镜（NC-AFM）和开尔文探针力显微镜（KPFM）对带有铂吸附原子的二氧化钛（TiO₂）（110）表面进行了研究。NC-AFM的形貌图像识别出吸附在三个不同位置的铂原子。这些位置分别在Ti原子行上、O原子行上以及O原子空位处。在Ti原子行上观察到了大多数铂吸附原子。连续记录的图像显示，Ti原子行上的铂吸附原子（吸附原子A）和O原子行上的铂吸附原子（吸附原子C）是可移动的，而O原子空位处的吸附原子（吸附原子B）则不可移动。在KPFM图像中识别出了吸附原子A和吸附原子B。然而，吸附原子C在KPFM图像中未被观察到，因为它们移动迅速或被探针扫出。KPFM测量结果表明，吸附原子A上的功函数比周围（1×1）表面的功函数低0.24 eV，而吸附原子B使功函数降低了0.26 eV。功函数的降低被解释为由于吸附原子向TiO₂衬底的电子转移，导致形成了一个指向真空的电偶极矩。在O原子空位中，吸附原子B与两个Ti原子接触，因此电子转移可以增强。
