Nanoscale-faceting of metal surfaces induced by adsorbates

Abstract

Using density functional theory and thermodynamic considerations, adsorbate-induced faceting of high-index metal surfaces such as Ir(210) and Re(112 1) has been studied. Focusing on these two systems we first discuss the adsorption behaviour of oxygen and nitrogen on the various surfaces relevant for the faceting, and afterwards use these energies to evaluate the stability of substrates and facets in the presence of oxygen and nitrogen. The faceting phase diagrams of Ir(210) and Re(112 1) show that both adsorbates enhance the anisotropy in surface free energy, finally causing nanofacets to become the thermodynamically favourable surface structure. We also generated analogous electrochemical phase diagrams for both surfaces in contact with an oxygen- or nitrogen-containing electrolyte and found that the same nanofacets should also become stable at positive electrode potentials. Thus, our calculations not only reproduce the experimentally observed surface faceting under UHV conditions, but also predict facet formation under electrochemical conditions.

Structure and stress of Re(112̄1); chiral terraces at a racemic surface

“…Ultimately the fully facetted surface appears after extensive exposure to oxygen at elevated temperature and is reported to contain pyramids of (10% 10), (01% 10), (10% 11) and (01% 11) oriented facets. 8,11,23,25 Thus we conclude that the step-bunches are caused by oxygen adsorption and that the step bunching is the pre-cursor to a micro-facetted surface matching that observed in ref. 25.…”

“…8,11,23,25 Thus we conclude that the step-bunches are caused by oxygen adsorption and that the step bunching is the pre-cursor to a micro-facetted surface matching that observed in ref. 25. While the intersection of the microfacets and surface now lead to a clearly zig-zag surface morphology the surface also shows bands of step edges and terraces running approximately parallel to [% 1100].…”

Restructuring of an Ir(210) electrode surface by potential cycling

“…While these tilt angles of the facets were verified experimentally both under UHV and electrochemical conditions [20–21], the presence of a superstructure on Ir(110) facets consisting of a stepped double-missing-row reconstruction also leads to a smaller tilt angle of only around 7° [21,37]. Fig.…”

“…While a sufficiently high coverage of oxygen species should be obtained under these conditions, potential cycling provokes the desired movement of surface atoms [36]. In addition, though faceting is thermodynamically driven, it is hindered (and limited) by the kinetic barriers involved in the atom rearrangement at the surface [37]. Thus, not only a critical adsorbate (here oxygen) coverage is required but also appropriate activation, allowing the system to overcome the kinetic barriers in the process of facet formation [23].…”

Emergent parabolic scaling of nano-faceting crystal growth

“…Certain planar interfaces of macroscopic single crystals can be thermodynamically induced to spontaneously decompose into fully faceted morphologies by thermal [16,17], chemical [7,[18][19][20][21] or electrochemical means [13,22]. Experimental observations of spinodally decomposing interfaces [23,24], such as those for thermally quenched Si(111) [17] or the oxygen-induced faceting of Cu(115) [19], reveal an ensuing coarsening of the resulting fully faceted interfaces, and the concomitant emergence of scaling regimes, wherein a power law governing the time t evolution of the characteristic length L of the interface's morphology appears [16,17],…”