Morphology of epitaxial magnetic alloy nanostructures grown on WSe₂(0001) studied by grazing-incidence small-angle X-ray scattering

The morphology of epitaxial alloy nanostructures grown on a van der Waals-type WSe₂(0001) surface was studied using grazing-incidence small-angle X-ray scattering (GISAXS). Assemblies of 111-oriented islands of (Co,Cr)Pt₃ and (Co,Fe)Pt alloys were grown at different deposition temperatures, with nominal thicknesses from 0.1 to 3 nm, resulting in various island densities. Evaluation of the GISAXS patterns indicates that for similar growth conditions CrPt₃ islands are flatter than CoPt or FePt islands and exhibit larger island volumes. These features are correlated with the better wetting behaviour and more negative formation enthalpy of the CrPt₃ alloy. For dense arrays of self-assembled CoPt islands, much smaller island volumes are extracted from GISAXS experiments than are observed by scanning tunnelling microscope imaging, which indicates that only the upper parts of the islands contribute to the GISAXS signal. Another aspect that needs to be taken into account for interpreting GISAXS patterns is the sensitivity of GISAXS to facetting and thus its capacity to extract the island shape. The latter is strongly dependent on the island size. For islands with an average volume smaller than ∼20 nm³, the shape cannot be determined unequivocally. Furthermore, for dense island assemblies with some size dispersity, the identification of steep side-wall facets from the GISAXS patterns is not straightforward as observed for truncated tetrahedron-shaped CoPt₃ islands.