NI ADSORPTION ON THE PRINCIPAL FACES OF A TUNGSTEN CRYSTAL - WORK FUNCTION CHANGES AND ADSORBATE DISTRIBUTION

The field electron microscope was used to study work function changes as a function of the amount of Ni deposition on a W tip at 78 K and annealed at various temperatures from 78 to 870 K. The work function changes were measured for the (I 10), (1 12), (111) and (100) faces of the W crystal. Strong differences were found in the work function changes for these four faces. The surface density of the adsorbate corresponding to the extreme of work function change for each face was equal to the reticular density of the substrate surface. On the basis of this, the distribution of the Ni adatoms on the surface of the W single crystal under the conditions of thermal equilibrium was determined. The results are compared with already known properties of the Ni/W adsorption system.