Li Shao-Chun, Wang Jian-guo, Jacobson Peter, Gong X-Q, Selloni Annabella, Diebold Ulrike
Department of Physics, Tulane University, New Orleans, Louisiana 70118, USA.
J Am Chem Soc. 2009 Jan 28;131(3):980-4. doi: 10.1021/ja803595u.
Adsorbate-induced band gap states in semiconductors are of particular interest due to the potential of increased light absorption and photoreactivity. A combined theoretical and experimental (STM, photoemission) study of the molecular-scale factors involved in the formation of gap states in TiO(2) is presented. Using the organic catechol on rutile TiO(2)(110) as a model system, it is found that the bonding geometry strongly affects the molecular electronic structure. At saturation catechol forms an ordered 4 x 1 overlayer. This structure is attributed to catechol adsorbed on rows of surface Ti atoms with the molecular plane tilted from the surface normal in an alternating fashion. In the computed lowest-energy structure, one of the two terminal OH groups at each catechol dissociates and the O binds to a surface Ti atom in a monodentate configuration, whereas the other OH group forms an H-bond to the next catechol neighbor. Through proton exchange with the surface, this structure can easily transform into one where both OH groups dissociate and the catechol is bound to two surface Ti in a bidentate configuration. Only bidendate catechol introduces states in the band gap of TiO(2).
由于半导体中吸附质诱导的带隙态具有增强光吸收和光反应性的潜力，因此备受关注。本文对TiO₂中带隙态形成所涉及的分子尺度因素进行了理论与实验（扫描隧道显微镜、光发射）相结合的研究。以金红石型TiO₂(110)上的有机儿茶酚为模型体系，发现键合几何结构强烈影响分子电子结构。在饱和状态下，儿茶酚形成有序的4×1覆盖层。这种结构归因于儿茶酚吸附在表面Ti原子排上，分子平面以交替方式从表面法线倾斜。在计算出的最低能量结构中，每个儿茶酚的两个末端OH基团之一解离，O以单齿构型与表面Ti原子结合，而另一个OH基团与相邻的儿茶酚形成氢键。通过与表面进行质子交换，这种结构可以很容易地转变为两个OH基团都解离且儿茶酚以双齿构型与两个表面Ti结合的结构。只有双齿儿茶酚会在TiO₂的带隙中引入态。
