Field Emission Microscope Study of Hg, NaI and I₂ Coadsorbed on W

Abstract

A field emission microscope was used to investigate the variation of the field emission pattern and work function of W due to the coadsorption of Hg, NaI and I₂.
When the W tip is annealed at 700 K, the average work functions are 3.7 eV both for NaI/W tip and NaI/Hg/W tip. In the case of adsorption of NaI on W covered with Hg, the average work function first decreases from 4.9 eV to the minimum value 4.6 eV with the amount of adsorbed NaI, after passing through the minimum, it increases till the final value of 5.6 eV.
When I₂ are adsorbed on the NaI/Hg/W tip, the average work function is 6.8 eV. This value is the same as these of I₂ /W system, indicating that the upper most adsorbed layer plays the dominant role in the determination of work function.