Microscope having atomic resolution with chemical sensitivity is one of the ultimate microscopes for the material science. Scanning tunneling microscope (STM) assisted by the core-level excitation by synchrotron radiation (SR) may be a possible candidate of such an ultimate microscope. In this paper we will demonstrate that we can observe element specific images of surfaces in the spatial resolution of several tens of nanometer by measuring the photon induced current images taken with an STM tip detecting the secondary electrons produced by the electron-hole recombination after the core-level excitation. Importance of the chemical contrast-enhancement by dividing the SR-STM image taken at photon absorption edge top by that of at the edge bottom is demonstrated by the observation of transition metal micro patterns. Possibility of a nanometer scale chemical imaging such as C60 domain structure on Si(111)√3×√3-Ag surface with an assistance of high-brilliant light sources is also suggested.
