Contrast inversion of photoelectron spectro-microscopy image

The contrast of a photoelectron microscopy image depends on the type of excitation photon source and the photoelectron kinetic energy. The contrast inversion observed in the photoelectron image by Hg lamp excitation is due to differences in work functions specific to materials and surface conditions, and the contrast inversion in the case of vacuum ultraviolet light excitation is due to the difference in the valence band density of states. The mechanism of contrast formation in valence photoelectron images is well understood qualitatively as described above, but quantitative evaluations are required for accurate understanding. We investigated the photoelectron image contrast of gold checkerboard pattern printed on the silicon wafer. The intensity of the gold region near the Fermi level is higher than that of the silicon substrate region, while the inverted contrast images were obtained at lower kinetic energies. We found that in the case of core and valence photoelectrons, certain contamination degrades the image quality, but in the case of Hg lamp excitation, it increases signal intensity owing to the lowering of work function. © 2021 The Japan Society of Vacuum and Surface Science. All rights reserved.