Development of SNOM/KFM probe microscope and investigation of optical properties of organic thin films with the microscope

我们成功地研制了一种近场光刺激和开尔文探针力检测的探针显微镜，使我们能够测量薄膜的表面电势，并通过光纤探头的孔径通过光照射来刺激表面。对Alq3薄膜表面电势的光致还原进行了深入的研究。从表面电势的光致图案化和光致还原对曝光时间/强度的依赖关系出发，研究了三(8-羟基喹啉)铝(III)(Alq3)薄膜表面电势的光致还原特性和机理。在n-Si(001)衬底上，300 nm Alq3薄膜的均匀表面电位为14-17V，通过接触掩模曝光可以得到空间尺度至少为700 nm的图形，并且图形可以在黑暗中保持一年以上。电位降低与曝光时间和/或曝光强度…的关系考虑到电子迁移率的Poole-Frankel公式，更能很好地与光激发载流子漂移引起的电势还原的计算相吻合。这些观察结果表明，Alq3表面电势的光致降低机理应该是光激发载流子的漂移。基于光致电子/空穴漂移降低表面电势的假设，通过拟合计算很好地再现了光致表面电势降低与光曝光强度的关系。从表面电势阶跃分布的KFM电势分布出发，讨论了KFM探针的二维传递函数。将扫描近场光学显微镜(SNOM)与KFM(SNOM-KFM)相结合，实现了光纤探头孔径近场光刺激。通过SNOM-KFM测量，可以将来自SNOM探头孔径的光电子能图可视化为Alq3薄膜上的表面电势图。较少

We have succeeded to develop a probe microscope with near-field optical stimulation and Kelvin probe force detection, which allows us to measure the surface potential of the thin films and to stimulate the surface by photo irradiation through the aperture of optical fiber probes. Photoinduced reduction of surface potential of Alq3 thin films have been intensively investigated as follows.The characteristics and mechanisms of photoinduced reduction of surface potential on tris(8-hydroxyquinolinato)aluminum(III) (Alq3) thin films are investigated and discussed from the results of photo-patterning of the surface potential and the reduction dependence on exposure time/intensity. The uniform surface potentials of 14-17 V in 300-nm Alq3 thin films on n-Si (001) substrates can be patterned by contact-mask exposure with spatial scales down to 700 nm at least, and the patterns remain more than one year in the dark. The dependence of potential reduction on exposure time and/or exposure intensity … More can be fitted well with the calculation of potential reduction due to the drift of photoexcited carriers with taking into account Poole-Frankel formula for the electron mobility. These observations indicate that the mechanism of photoinduced reduction of surface potential of Alq3 should be the drift of photoexcited carriers.The dependence of photo-induced reduction of surface potential on photo-exposure intensity is reproduced well by fitting calculation based on the assumption that the drift of photo-excited electrons/holes decreases the surface potential. Two-dimensional (2D) transfer functions of KFM probes are discussed from KFM potential-profiles obtained for a step pattern of surface potential. Near-field optical stimulation through an aperture of an optical-fiber probe is demonstrated as scanning near-field optical microscope (SNOM) combined with KFM (SNOM-KFM). A photoemission pattern from an aperture of SNOM probes can be visualized as a surface-potential pattern on Alq3 thin films by means of SNOM-KFM measurements. Less