Oscillatory adatom–adatom interactions of Pd adatoms on the W(2 1 1) surface

Direct observations with the field ion microscope make it possible to determine the probability P(R) of finding two atoms on a surface at a separation R at equilibrium at temperature T. The free energy of interaction F(R) can be obtained from the relation: P(R)∝exp[−F(R)/kT]. On the W(2 1 1) plane, the interactions of two Pd atoms are studied for following cases: two Pd atoms in the same, in the nearest, the second-nearest and the third-nearest neighbor channels. When two Pd atoms are in the same channel, they combine easily to form a dimer of bond length 2.74 Å and the dimer can diffuse along the channel. Oscillatory behaviors of these interactions along the channel direction are observed. The further are the channels separated, the smaller is the maximum interaction energy. The maximum attractive energy in the same, nearest, second-nearest and third-nearest neighbor channel separations are 33.1, 23.0, 7.8, and 7.1 meV, respectively.