Interaction between photocatalyst surface nanostructures and ultraviolet light by apertureless scanning nearfield optical microscopy

扫描隧道显微镜(STM)观察到，紫外光照射二氧化钛表面产生了明显的结构变化，这是紫外光对二氧化钛表面进行电子激发的结果。本文用扫描隧道显微镜在原子尺度上显示了金红石型二氧化钛(110)表面的局域光响应。根据最小禁带宽度(3.2 eV)电子跃迁，(110)表面几乎所有区域都对325 nm紫外光有响应，台阶和(1×2)脊区具有较高的响应强度。当用442 nm的蓝光照射同一表面时，大部分表面处于休眠状态，但阶跃区和(1×2)脊结构的某些区域对蓝光有响应。这些位置与表面的氧缺位有关，这可能为二氧化钛光催化剂在可见光下进行表面工程提供线索。我们还对由MDMO-PPV：PCBM混合物组成的经典有机太阳能电池系统进行了全面的开尔文探针力显微镜(KPFM)研究。KPFM方法得到了纳米尺度的地形和局部功函数的详细信息。实验在黑暗或442 nm或675 nm激光照射下进行，以提取局部分辨的表面光电压(SPV)。我们发现氯苯和甲苯共混膜表面的能级有明显的差异。结合高分辨率扫描电子显微镜(SEM)实验，我们能够解释KPFM的结果，并得出一些关于太阳电池配置中电子向阴极传输的结论。结果表明，在有机太阳能电池中，甲苯浇铸的薄膜表面阻止了电子向阴极的传播，电子通常蒸发在薄膜的顶部。

Ultraviolet (UV) irradiation on titanium dioxide surface gives apparent structural changes as observed by scanning tunneling microscopy (STM), which are the consequence of electronic excitation of the surface by UV light. Here local photoresponse of a rutile TiO_2(110) surface is visualized at atomic scale by STM. Almost all the areas on the (110) surface responded to the illumination of 325-nm ultra-violet (UV) light, in accordance with the minimum band-gap (3.2eV) electron transition, with steps and (1×2) ridge areas exhibiting higher response intensities. When the same surface is illuminated with blue light at 442nm, which is well below the minimum band-gap transition energy, most of the surface areas were dormant, but certain areas at step regions and (1×2) ridge structures responded to the blue light. These sites are associated with oxygen deficiency on the surface, which may give a clue to the possibility of surface engineering of titania photocatalyst to be employed under visible light.We also conducted a comprehensive Kelvin probe force microscopy (KPFM) study on the "classical" organic solar cell system consisting of MDMO-PPV:PCBM blends. The KPFM method yields detailed information of topography and local work function at nanometer scale. Experiments were performed either in dark or under laser illumination at 442nm or 675nm to extract the locally resolved surface photovoltage (SPV). We identified distinct differences in the energetics on the surface of chlorobenzene and toluene cast blend films. Together with high resolution scanning electron microscopy (SEM) experiments we were able to interpret the KPFM results and to draw some conclusions for the electron transport towards the cathode in the solar cell configuration. The results suggest a blocking behavior of the toluene cast film surfaces against electron propagation towards the cathode, usually evaporated on top of the films in organic solar cells.