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

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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