Novel Microscopic Mechanism of Intermixing during Growth on Soft Metallic Substrates

Abstract

Generic computer simulations using empiric interatomic potentials suggest a new, collective mechanism that could be responsible for mixing at heteroepitaxial interfaces. Even if single adsorbate atoms diffuse by hopping on the substrate surface and do not mix at the terraces, two-dimensional islands formed by nucleation may become unstable above a certain critical size and explode upwards forming clusters of several atomic layers. This process is accompanied by strong distortions of the underlying atomic layers, and on soft materials it can result in surface etching and incorporation of substrate atoms into the islands.

Surfactant effect in heteroepitaxial growth: The Pb-Co/Cu(111) case

“…Multiple height island formation, step decoration, vacancy (pools) islands and Cu-Co intermixing are common features in this system [9,10]. In a recent work, we showed that this behavior depends on the adsorbate -substrate interaction, and it should be awaited any time materials of these types are put into contact [11].…”

Atom-wide Co wires on Cu(775) at room temperature

“…An earlier theoretical study by Gomez et al [10] using Monte Carlo and static relaxation provides a second interesting comparison of Co growth on Cu(111). In part, this study looked at preferential nucleation sites of Co at Cu steps and drew the following conclusions: (1) Co atoms will form "two nearly straight rows", one in front of the Fig.…”

“…In summary, despite extensive prior work in the Co/Cu materials systems, no atomic wires of Co on Cu(111) surfaces were observed experimentally, although the existence of Co wires at Cu step edges was predicted theoretically [10,11]. Note, however, that there are several reports of the direct observation of atomic wires in different bi-metallic systems, e.g.…”

“…These chains appeared as 4Å-high protrusions at the step edge and thus were neither single-atom in width or height. Finally, Monte Carlo simulations [10] and density functional theory (DFT) calculations [11] have been used to investigate the self-assembly mechanism of Co wires at a Cu(111) step. Though there are differences in the details of their predictions of an atomic-wire surface phase, both suggested that laterally encapsulated Co wires are formed during self-assembly.…”

Atomistic Modeling Of Co Growth On Cu(111)

“…STM experiments [7] also suggest that the islands include a subsurface Co layer. In addition, theoretical calculations using empirical interatomic potentials indicate that two-dimensional Co islands become unstable above a certain critical size and "explode" upwards, dragging Cu atoms from the surface layer forming mixed- composition islands several layers high [8].…”