Charge-State Field Evaporation Behavior in Cu(V) Nanocrystalline Alloys

Atom probe tomography (APT) of a nanocrystalline Cu-7 at.% V thin film annealed at 400°C for 1 h revealed chemical partitioning in the form of solute segregation. The vanadium precipitated along high angle grain boundaries and at triple junctions, determined by cross-correlative precession electron diffraction of the APT specimen. Upon field evaporation, the V2+/(V1+ + VH1+) ratio from the decomposed ions was ~3 within the matrix grains and ~16 within the vanadium precipitates. It was found that the VH1+ complex was prevalent in the matrix, with its presence explained in terms of hydrogen's ability to assist in field evaporation. The change in the V2+/(V1+ + VH1+) charge-state ratio (CSR) was studied as a function of base temperature (25-90 K), laser pulse energy (50-200 pJ), and grain orientation. The strongest influence on changing the CSR was with the varied pulse laser, which made the CSR between the precipitates and the matrix equivalent at the higher laser pulse energies. However, at these conditions, the precipitates began to coarsen. The collective results of the CSRs are discussed in terms of field strengths related to the chemical coordination.