Structural and electronic properties of molecular beam epitaxially grown Ni1+xTiSn films

- Ni1+xTiSn films are successfully grown with molecular beam epitaxy.
- X-ray diffraction shows (0 0 4) peaks that can be fit as two components.
- TEM reveals regions of both full-Heusler and half-Heusler ordering.
- RHEED patterns change above x = 0.30 and is attributed to a change in surface termination.
- Resistivity (ρ) and the Seebeck coefficient (S) increases for small values of x.

This paper demonstrates the molecular beam epitaxial growth of metallic full-Heusler Ni2TiSn precipitates within semiconducting NiTiSn host matrix, and discusses the structural and chemical stability of this biphasic epitaxial composite and its influence on the electronic properties. Structural properties of the epitaxial films were characterized by in-situ reflection high-energy electron diffraction and ex-situ by X-ray diffraction and transmission electron microscopy. The results indicate the presence of a secondary phase with full Heusler ordering within half-Heusler host matrix. Both the parent half-Heusler and the secondary full-Heusler phases in the epitaxial films are strained from their bulk lattice parameters. Electronic properties show an increase in resistivity at low Ni excess.