O the Characterization of Electroless Nickel Thin Films Produced with the Reducing Agent, Dimethylamine Borane

Nickel-boron films were prepared using an electroless deposition technique with dimethylamine borane as the reducing agent. The coatings were plated from Ni baths of pH 6.0 and 77^circC and contained 19 to 33 at.% B. The structure and crystallization behavior of as-plated and heat-treated coatings were investigated using optical and scanning electron microscopy, x-ray pinhole diffraction, Auger spectroscopy, transmission electron microscopy and differential scanning calorimetry (DSC). Coatings were annealed at temperatures ranging from 200 to 600 ^circC for 1 hour in atmospheres of rm H_2, N_2 and vacuum (10^{-6} Torr). The microstructure of the as-plated films was modeled as one consisting of pure microcrystalline Ni grains (20 to 90 A), surrounded by B. The B was not uniformly distributed throughout the coating. The structure transformed to one consisting of larger Ni grains (9 to 100 nm) with rm Ni_3B and rm Ni_2B precipitates as the heat-treating temperature increased. An Auger study demonstrated that the B concentration varied greatly with depth and that B segregated towards the surface with increasing temperature, especially in N_2. As-deposited coatings were also heated from room temperature to 460^circC in a DSC cell in N_2 at various heating rates. Three exothermic reactions were observed and associated with the formation of NiO, Ni_3B and Ni_2B, in that order. An activation energy and reaction order of 35.6 Kcal/mol and 1.65, respectively were associated with the formation of Ni_2 B,, according to a phase boundary reaction model. It was also empirically determined that the heat capacity of NiB, Ni_2B and Ni_3 B followed a model of the form, rm C_{p}=a+bT- c/T^2 (cal/mol deg). At 300^circK, the C _{rm p}'s of NiB, Ni_2B and Ni_3B were determined to be 9.3, 15.1 and 21.2 (cal/mol deg), respectively.