Epitaxial growth and stabilization of transition metal nitride-based superlattices and buffer layers

The epitaxial stabilization of cubic, non-equilibrium AlN in epitaxial, AlN/TiN, AlN/VN, and AlN/W superlattices was investigated. While the bulk stable structure of AlN is hexagonal wurtzite, cubic rocksalt structure AlN was epitaxially stabilized in AlN/TiN superlattice and AlN/VN superlattices. The films were characterized using X-ray diffraction (XRD), simulations of XRD patterns, cross-sectional transmission electron microscopy (XTEM) and Low Energy Electron Diffraction (LEED). The effect of superlattice period Λ, total film thickness, AlN layer thickness fraction (l_AlN/Λ) and coherency strain on epitaxial stabilization were studied. The mechanical properties of the AlN/TiN superlattices were investigated by nanoindentation. It was found that zinc-blende AlN was stabilized in AlN/W superlattices, whereas rock-salt AlN was stabilized in AlN/NbN superlattices suggesting that the symmetry of the underlying template affected stabilized phase.; The second area of focus of this research was the growth and characterization of epitaxial transition metal nitride buffer layers. The study was geared towards the development of a commercially viable buffer layer between the superconducting perovskite oxides such as Yttrium barium Copper Oxide (YBCO) and reactive Ni substrates. High quality TiN and VN buffer layers were grown on MgO and Ni RABiTS (Rolling Assisted Biaxially Textured Substrate) and structurally characterized by XRD, High Resolution SEM and TEM. High quality YBCO layers were subsequently grown on TiN with thin (<100nm) MgO and ceria layers as a intermediate oxide layers in order to prevent oxidation of nitride layers. Relatively high Jc (6 × 105 A/cm2) and Tc (∼89K) were demonstrated for YBCO layers. Epitaxial YSZ on TiN was studied for a potential alternative intermediate oxide.