ADSORPTION STUDIES OF COBALT ON TUNGSTEN(110), TUNGSTEN(100) AND TUNGSTEN(111) PLANES BY PROBE-HOLE FIELD-EMISSION MICROSCOPY

The changes in the work function, Delta phi, and in the Fowler-Nordhei m pre-exponential factor, In B, have been investigated for cobalt adso rption on tungsten (110) (100) and (111) planes by probe-hole field em ission microscopy. The workfunction variations have been found to be s trongly dependent on the temperature in the range 300-580 K on these p lanes. Delta phi decreases with submonolayer coverages of cobalt on th e W(110) and W(100) planes. On the W(111) plane, Delta phi initially d ecreases and then exhibits a jump towards positive values at relativel y higher doses. This abrupt increase in Delta phi and the correspondin g zero crossover of In B have been attributed to surface reconstructio n. The results are discussed in terms of the electronic structure and the degree of strain produced in the pseudomorphically grown cobalt la yers on various crystallographic planes of tungsten.