Structural properties of molecular beam epitaxy grown Ni/Pt superlattices

Abstract

We find that the [Ni3.2nmPt1.6nm] × 15 and [Ni3.2nmPt0.8nm] × 15 multilayers are semicoherent and display a columnar morphology. From both the period of the moir’e fringes and the positions of the diffraction peaks in electronic (plan-view and crosssection geometries) and x-ray diffraction patterns, one deduces that the nickel is relaxed (at least in the error bars of all our measurements), whereas the platinum remains slightly strained (≈−1%). The interfaces are sharp; no intermixing takes place giving rise to neat contrasts in transmission electron microscopy (TEM) and to high intensities of the superlattice peaks in the growth direction in both diffraction techniques. The relaxation of the interfacial misfit occurs partially through misfit dislocations, partially through the strain of platinum. A quasiperiodic twinning occurs at the interfaces, the stacking fault which forms the twin being the most often located at the interface Pt/Ni, i.e., when a Pt layer begins to grow on the Ni layer. The simulation of the θ/2θ superlattice peak intensities takes into account the columnar microstructure. It shows that the roughness is predominantly at medium scale with a fluctuation of about 12.5% for Ni layers and negligible for Pt layers.