[en] Highlights: • MBE of Er and Gd on vicinal Si(1 1 1) investigated by STM, RHEED and LEED. • RE-silicide epitaxial nanostructures characterized by quasi-1D reconstruction. • Diffuse scattering caused by linear disorder between reconstructed nanostructures. • Surface disorder causes extinction of half-order satellites in diffraction patterns. Sub-monolayer epitaxial self-assembled silicides of Er and Gd on Si(1 1 1) exhibit unique structural and morphological features that play a crucial role in their magnetic behavior. The effects of disorder occurring between the characteristic quasi-1D surface reconstructions of such systems were analyzed by low energy (LEED) and reflection high energy (RHEED) electron diffraction. The observed Rare-Earth Metal (REM)-Si antiphase domains caused appearance of diffuse intensity planes in the surface reciprocal space, visualized as straight (arched) streaks in LEED (RHEED) diffraction patterns. Random registry shifts between adjacent adsorbate atomic chains caused extinction of the half-order satellites in diffraction patterns of a surface reconstruction identified by scanning tunneling microscopy (STM) as Si(1 1 1)-(3 × 2)-Gd.

[en] Surface science techniques (STM, STS, and XPS) were combined with ab initio simulations to detect the local crystal structure and chemistry. Solid phase epitaxy of iron on vicinal Si(111) substrate resulted in the formation of $\left(\sqrt{3}\times \sqrt{3}\right)$R30° nanoislands and (2×2) films of γ-FeSi₂(111). We identify these structures by comparing experimental normalized derivative conductance curves with tomographic simulated local density of states (LDOS). The thermodynamic tendency of γ-FeSi₂(111) towards Si rich surfaces is manifested in Si rich termination layers and reconstructions. We show that a weighted average of the LDOS from the Fe layer and the reconstruction layer can explain the main states in the normalized derivative conductance curves, enabling in-situ identification of crystal structure and composition of epitaxial deposits.

[en] We used solid phase (SPE) and reactive deposition (RDE) epitaxy to grow crystallographically identical – but morphologically different – islands. Tetragonal α-FeSi₂ islands crystallized pseudomorphically in the α-FeSi₂(1 1 2)1 1 0||Si(1 1 1)1 1 0 and α-FeSi₂(1 1 0)1 1 1||Si(2 2 0)1 1 2 orientation relations, with flat (2 × 2)-reconstructed top facets. The SPE-grown islands self-ordered in the form of 1D chains decorating the vicinal Si(1 1 1) step bunch edges along a specific $\left[1\overline{1}0\right]$ direction. The RDE-grown islands elongated along three equivalent $〈11\overline{2}〉$ directions, and were typically shorter, narrower, and thinner than the SPE-grown ones. In both cases, vast majority of the islands evolved sufficiently close to one another to enable dipolar interactions. Analyzing response to applied magnetic field, we identified areas of the island perimeter rims as the source of uncompensated magnetic moments creating the superspins, lateral island shape anisotropy as the origin of magnetic anisotropy, and periodic 1D ordering of interacting SPE-islands as the origin of superferromagnetic order. In contrast, three-fold orientational domains of the smaller RDE islands showed behavior more consistent with a superspin glass state. The above comparison emphasizes importance of the number of atoms at the island perimeter rims, and the role of dipolar interactions between the islands, for the magnetic behavior of the system.