Point-defect properties of and sputtering events in the {001} surfaces of Ni₃Al I. Surface and point-defect properties

Constant-area and fully relaxed molecular dynamics methods are employed to study the properties of the surface and point defects at and near {001} surfaces of bulk and thin-film Ni, Al and Ni₃Al respectively. The surface tension is larger than the surface energy of all {001} surfaces considered in the sequence: Al (1005 mJ m^-2) < Ni₃Al (mixed Ni-Al plane outermost, 1725 mJ m^-2) < Ni₃Al (all-Ni-atoms plane outermost, 1969 mJ m^-2) < Ni (1993 mJ m^-2). For a surface of bulk Ni₃Al crystal with a Ni-Al mixed plane outermost, Al atoms stand out by 0.0679 Å compared with the surface Ni atoms and, for the all-Ni-atoms surface, Al atoms in the second layer stand out by 0.0205 Å compared with Ni atoms in the same layer. Vacancy formation energies are about half the bulk values in the first layer and reach a maximum in the second layer where the atomic energy is close to the bulk value but the change in embedding energy of neighbouring atoms before and after vacancy formation is greater than that in the bulk. Both the vacancy formation energy and the surface tension suggest that the fourth layer is in a bulk state for all the surfaces. The formation energy of adatoms, antisite defects and point-defect pairs at and near {001} surfaces of Ni₃Al are also given.