Effect of temperature and environment on the structure of thin single-srystal nickel films

Abstract

Annealing experiments under varying conditions of temperature and pressure have been carried out along with transmission electron diffraction from thin single-crystal films of nickel. The single-crystal films were epitaxially grown by vapor deposition on heated, freshly cleaved (100) faces of rocksalt, and the annealing experiments were carried out in the diffraction instrument after the films had been floated off the rocksalt and mounted on Ni grids. The diffraction patterns of the as-grown films indicated that the Ni was a {001}-oriented single crystal with faulting that resulted in streaking in all four [111] directions. The {111} faults were removed by annealing above 500°C for 1 h at less than 1×10-5 Torr. At 400°C and vacuum pressures controlled by leaking air into the diffraction unit, structural changes were observed. At 1×10-5 Torr, the film remained single crystal; at 3×10-5 Torr, the electron diffraction patterns indicated faults in the [111] directions; and as the pressure increased to 5×10 -5 Torr, Ni plus the previously reported metastable Ni+O phase appeared. A new complex two-phase structure of Ni plus Ni+O occurred at 7×10-5 Torr; and at 1×10-4 Torr, only the equilibrium NiO phase was observed. At higher temperatures and a constant pressure of 3×10-5 Torr, there was an absence of any transition phases. Experiments were repeated with argon under similar conditions and no structural changes were observed. The changes are attributed to an increasing oxygen content in the film during the annealing conditions. The transformations are interpreted to be dependent upon a complex type of precipitation in which the oxygen fault interpretation postulated by Heidenreich et al. may be the first stage in the precipitation of NiO in the film. © 1964 The American Institute of Physics.