Adsorption studies of iron on tungsten by probe-hole field emission microscopy

Probe-hole field emission microscopy has been used to study submonolayer and monolayer amounts of iron on various tungsten planes. The adsorption is found to be insensitive to the substrate deposition temperatures of 300, 600, and 1100 K as seen by the variation of the workfunction and the pre-exponential factor with the adsorbate doses. The workfunction of the adsorbate covered surface reduces in case of the (110), (100), and (112) tungsten planes, while it increases in case of the (111) and (116) planes, becoming coverage independent with a workfunction of 4.6 eV. This has been atributed to surface alloying of iron atoms with tungsten because of the structure of these two planes. The results are discussed in the light of the existing experimental results on metallic adsorbates on tungsten.