A clean surface of LaB//6(210) has the low work function of 2. 2 plus or minus 0. 1 eV at room temperature, which is lower than those of the (100), (110), and (111) surfaces. La atoms exist in a (1 multiplied by 1) ordered structure at the outermost layer of the (210) clean surface. The value of the low work function of LaB//6 is discussed on the basis of the data together with the Lang-Kohn theory. The work function changes from 2. 2 to 3. 1 eV with oxygen exposure and saturates above about 15 L; the periodicity of the surface-atomic lattice disappears almost completely.
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