Measurement of photo‐patterned surface potential of Alq 3 thin films by Kelvin‐force microscope together with near‐field optical stimulation

Uniform and extremely high surface potentials of tris(8‐hydroxyquinolinato) aluminum(III) (Alq 3 ) thin films, formed spontaneously by vacuum evaporation of Alq 3 in the dark, are patterned by contact‐mask photo‐exposure. The resulting surface‐potential patterns are observed by scanning‐probe Kelvin‐force microscope (KFM). Surface‐potential patterns on Alq 3 thin films can be preserved in the dark for more than a year at − 20 °C. The dependence of photo‐induced reduction of surface potentials 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 Alq 3 thin films by means of SNOM‐KFM measurements. Copyright © 2008 John Wiley & Sons, Ltd.