Measurement of photo-patterned surface potential of Alq3 thin films by Kelvin-force microscope together with near-field optical stimulation

• Published in: Surface and interface analysis 2008-03, Vol.40 (3-4), p.810-813
• Main Authors: Ozasa, Kazunari, Nemoto, Shigeyuki, Isoshima, Takashi, Ito, Eisuke, Maeda, Mizuo, Hara, Masahiko
• Format: Article
• Language: English
• Subjects: Alq3; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; KFM; near field; Physics; SNOM; surface potential; transfer function
• ISSN: 0142-2421; 1096-9918
• DOI: 10.1002/sia.2669

Uniform and extremely high surface potentials of tris(8‐hydroxyquinolinato) aluminum(III) (Alq3) thin films, formed spontaneously by vacuum evaporation of Alq3 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 Alq3 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 Alq3 thin films by means of SNOM‐KFM measurements. Copyright © 2008 John Wiley & Sons, Ltd.