Compositional and structural studies of nanoscale boron-doped nickel aluminide films

This thesis presents a detailed investigation of the composition and microstructure of boron-doped nickel aluminide thin films fabricated via ion beam sputtering. Findings are related to film growth mode, fabrication conditions, and mechanical properties.; Results from the characterization of the composition and structure of Ni₃Al:B films having thicknesses ranging from ∼300 to ∼2600 Å deposited on substrates of plastic, NaCl and Si at a temperature of ∼300 K by Kaufman-type ion beam sputtering of a Ni₃Al:B compound target are reported. The bulk composition of the films was investigated using instrumental neutron activation analysis (INAA) and Rutherford backscattering spectrometry (RBS). It was determined by INAA and RBS that the bulk Ni/Al atomic ratio of the target can be replicated in films fabricated on single crystal NaCl substrates. However, results from the measurement of the local composition by energy dispersive X-ray (EDX) and electron energy loss spectroscopy (EELS) via scanning transmission electron microscopy (STEM) reveal that the local Ni/Al atomic ratio is higher. This is the result of preferential sputtering of Ni due to recoil implantation of Al in the compound Ni₃Al:B target. The spatial distribution of boron in the films was determined via neutron depth profiling (NDP).; Grazing incidence X-ray diffraction studies reveal that films grown on Si and NaCl are polycrystalline and show the (111) crystallographic plane. The absence of superlattice peaks at (100), (110), (210) and (211) in the diffraction spectra indicate that the films are also in a state of disorder. It was determined from annular dark field images produced via STEM of 300, 560 Å, and 600 Å thin films that the average size of grains was 30 ± 3 Å. This cluster size is characteristic of films that have a very fine-grain microstructure and yield stresses of hundreds of MPa since the yield stress increases with decreasing grain size. The coalescence of clusters as observed via BF and DF images indicate that the growth mode of these films is best described by the Volmer-Weber (VW) model.