ADSORPTION STUDIES OF IRON ON TUNGSTEN BY PROBE-HOLE FIELD-EMISSION MICROSCOPY

Probe-hole field emission microscopy has been used to study submonolay er and monolayer amounts of iron on various tungsten planes. The adsor ption is found to be insensitive to the substrate deposition temperatu res of 300, 600, and 1100 K as seen by the variation of the workfuncti on and the pre-exponential factor with the adsorbate doses. The workfu nction of the adsorbate covered surface reduces in case of the (110), (100), and (112) tungsten planes, while it increases in case of the (1 11) and (116) planes, becoming coverage independent with a workfunctio n of 4.6 eV. This has been attributed to surface alloying of iron atom s with tungsten because of the stricture of these two planes. The resu lts are discussed in the light of the existing experimental results on metallic adsorbates on tungsten.