An apparatus for alternative observation of low energy electron diffraction (LEED) and the photoelectric emission has been built to study the surface state of solids. This LEED equipment has both the advantages of pattern display type using a fluorescent screen and collector scanning type. The experimental tube is evacuated pressures below 1.3 × 10
-9 torn As the examples of the data obtained with this apparatus, the photoelectric work function and LEED patterns from (100) face of a nickel crystal under identical conditions in the ultrahigh vacuum region have been shown. Crystals heated at 970°C for one hour showed diffraction patterns corresponding to C (2×2) structure, while the one not heated to high temperature showed only a diffuse background, the work function for the former being 1.2 eV higher than the value 4.15 eV for the latter.
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