The quantitative compositional analysis and field-evaporation behavior of ordered Ni 4Mo on an atomic plane-by-plane basis: An atom-probe field-ion microscope study
Atom-probe field-ion microscope analyses were performed on specimens of ordered Ni 4Mo. The (211) fundamental and (101) superlattice planes, of the body-centered tetragonal lattice, were analysed chemically on an atomic plane-by-plane basis. It was demonstrated that the composition of each individual plane can be determined as a function of depth without any ambiguity. The overall coverage Mo concentration was measured to be 17.1 at% for the (211) fundamental plane — as compared to 19.4 at% Mo by conventional chemical techniques. Possible sources of this discrepancy are discussed. The details of the field evaporation behavior of the (211) fundamental and (101) superlattice planes were studied. The field evaporation behavior is described in terms of the field evaporation rate, the order of the field evaporated ions, etc. Each individual atomic plane field-evaporated on an atomic plane-by-plane basis for the (211) fundamental plane. While for the (101) superlattice plane a group of planes consisting of one plane of Mo atoms and four planes of Ni atoms field-evaporated as a unit. An abnormal increase in the number of Mo atoms was found in the central portion of the (211) fundamental plane. Possible mechanisms for the abnormal field evaporation rate are discussed. Finally, it is concluded that the atom probe technique can be used, in this complicated ordered structure, to follow: (1) the physics and chemistry of the field evaporation process; and (2) the chemistry of the alloy as a function of position, on a subnanometer scale, throughout the specimen.