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43258-G5
Fundamental Studies of Epitaxial Nucleation and Growth of Conductive-Oxide Thin Films on Highly Reactive, Single-Crystal-Like Textured Metal Substrates

Tolga Aytug, University of Tennessee

As a component of our research on conductive buffer layer growth on highly reactive single-crystal-like textured Ni-3%W and pure Cu substrates, deposition and growth studies of Ni3Al metal seed layers were conducted by dc-magnetron sputtering. We have chosen Ni3Al as a candidate material because it is an ordered superalloy compound with high strength and oxidation resistance at elevated temperatures. Note that, during the high temperature steps of high temperature superconductor (HTS) deposition, it becomes indispensable to protect the metal substrate from oxidation by means of a barrier seed layer. This layer blocks oxygen diffusion and at the same time remains electrically conductive. In this work, processing parameters that control the film nucleation and evolution were assessed. Under optimized conditions, epitaxial phase formation on both Ni-3%W and Cu substrates was achieved. Energy dispersive X-ray analysis indicated that the Ni3Al films are stoichiometric in composition. On both substrates, we have demonstrated that a Ni3Al layer has an ideal electrical coupling to the metal substrate. In addition, x-ray diffraction and scanning electron microscopy observation of Ni3Al/Ni-3%W architecture revealed excellent crystallographic and microstructural properties. Atomic force microscopy analysis showed smooth Ni3Al surface morphology with a surface roughness of Ra<1 nm, similar to that of the underlying substrate. These results demonstrate that Ni3Al may provide a fully conductive architecture suitable for such applications as transmission lines and fault current limiters. For the latter, the resistance of the structure in the non-superconducting state could be tailored by the alloy tape that is coupled to the superconducting layer. Future work will focus on assessing the general usefulness of Ni3Al as well as NiAl as a seed buffer layer, and efforts will be put forward to make Ni3Al compatible for the deposition of a superconducting layer. To achieve this we will investigate the underlying principles and parameters that control the epitaxial nucleation of the conductive-oxide thin films on Ni3Al and NiAl.

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