Microstructural characterisation of epitaxial rare earth metal based films

Epitaxial rare earth films and superlattices grown by molecular beam epitaxy, MBE, can be designed to investigate theoretical predictions of the magnetic and electronic properties of the metals. These investigations ideally require smooth epitaxial layers with atomically flat interfaces and therefore the microstructure of selected epitaxial rare earth systems has been characterised by a combination of techniques. These systems were grown on a (110) niobium ∥ (11̅20) sapphire substrate. Because the crystallographic quality of the subsequent layers is influenced by the quality of the substrate, the niobium-sapphire interface was studied with transmission electron microscopy, TEM, and high resolution electron microscopy, HREM, to identify uniquely the misfit dislocation network. Conventional TEM specimen preparation techniques were inappropriate for the preparation of metallic foils, and so appropriate specimen preparation techniques were developed. HREM was used to characterise the strain relief mechanisms within a partially relaxed holmium/yttrium superlattice. Rare earth hydrides are also of interest because of the ability of some rare earths to absorb up to three hydrogen (H) atoms per rare earth atom. Loading between RH2 (R - rare earth) and RH3 is completely reversible and the system undergoes a metal-insulator transition. A film subjected to such H-loading is observed to switch from mirror-like to transparent. TEM specimens of RH2 (R = Ho, Y) were characterised and the structural changes that occur during H-loading were investigated using controlled environment TEM and a combination of scanning probe techniques. The applicability of electron diffraction for the characterisation of structures containing hydrogen is presented. Finally single crystal neutron diffraction techniques have been applied to epitaxial samples of HoD2 to probe the effect of the addition of extra deuterium atoms on the magnetic properties.