Mechanism of Interlayer Transport on a Growing Au(111) Surface: 2D vs. 3D Growth Abid Ali a , Hannes J´onsson a,b a Science Institute and Faculty of Physical Sciences, University of Iceland, VR-III, 107 Reykjav´ık, Iceland b Dept. of Chemistry, Brown University, Rhode Island 02912, USA Abstract The atomic scale transitions corresponding to diffusion and interlayer transport of a Au adatom on the low energy, close packed Au(111) surface are studied using density functional theory calculations within the generalized gradient ap- proximation. Minimum energy paths and estimates of activation energy are calculated for processes that influence whether the crystal grows layer-by-layer, i.e. 2D growth, or whether new islands tend to nucleate on top of existing is- lands resulting in 3D growth. Kinks on island edges turn out to provide paths for adatom descent with lower activation energy than straight steps. The energy barrier for an adatom to round the corner and enter a kink site is significantly higher. A descent mechanism that places an adatom near but not at a kink site can therefore promote the formation of a new row of step atoms and lead to the introduction of additional kink sites, thereby opening up new low activation energy paths for descent and promotion of 2D growth. The sites adjacent and above the step edge provide large binding energy for the adatom, especially at the B-type step, and form a trough along which the adatom can migrate before descending, thereby increasing the probability that an adatom finds a kink on the B-type step. These features of the energy landscape representing the inter- action of a Au adatom with the surface point to the possibility of a re-entrant layer-by-layer growth mode of the low energy, close packed surface of the gold crystal. 1. Introduction In some material growth applications the goal is to form nanoscale islands on a surface while in others the preferred growth mode is layer-by-layer. The morphology of the surface is typically governed by kinetic processes rather than thermodynamics because the surface temperature is kept low enough to prevent the mixing of components. An important consideration then is the rate of vari- ous atomic rearrangement processes, in particular those that lead to descent of adatoms from an upper layer to a lower layer, i.e. interlayer transport. Such Preprint submitted to Surfaces and Interfaces March 23, 2022