Laser-based photoemission micro-spectroscopy for occupied and unoccupied states of inhomogeneous surfaces

Performance of our micro-spot photoemission spectrometer based on fs-laser radiation has been applied to observe (a) surface images due to an unoccupied electronic state and (b) inhomogeneous electronic structure of a thin organic film. Two-photon photoemission spectroscopy was performed with lateral resolution of 0.6 μm for a polycrystalline copper plate. We have observed lateral distribution of the unoccupied image-potential state of Cu(1 1 1) surface. In addition to μm-scale information from the surface image, the high-energy resolution spectroscopy provides insight on the step size of nm-scale. By employment of focused VUV light of 8.86 eV, one-photon photoemission spectroscopy was performed for a copper phthalocyanine film grown on the polycrystalline copper plate with a lateral resolution of 0.3 μm and an energy resolution of 30 meV. The photoemission band due to the highest occupied molecular orbital peaked at the binding energy of either 1.6 or 1.2 eV depending on the sample positions. Polarization dependence of the band showed that molecules are poorly oriented even on the (1 1 1) surface. The results demonstrate that a large inhomogeneity exists in the interface electronic structure.