(Invited) The Dualism between Adatom and Vacancy-Based Single Crystal Growth Models

Abstract

In homoepitaxial crystal growth, four basic growth morphologies (idealized growth modes) have been established that describe the deposition of atoms on single crystal surfaces: step-flow, layer-by-layer, mound formation, and random/self-affine growth. Mound formation leads to nano-scale surface patterning. However, the formation of (nano)-islands, patterns, and roughness occurs also during ion bombardment, electrochemical etching and oxidation/reduction cycling. Here we show, in analogy to many particle/anti-particle formalisms in physics, the existence of the dualism between individual adatom- and single vacancy-growth modes. We predict that all standard adatom growth modes do exist also in their counter, vacancy version. For the particular case of mound formation, we derive the theoretical equations and show the inverse similarity of the solution. We furthermore treat simultaneous growth by adatoms and vacancies, and derive the analytical solution of the growth shape evolution of the mounds [1]. Applying repeated oxidation-reduction cycles (ORCs) to a Pt(111) surface, we even present an experimental verification, in which both adatom and vacancy mound formation is active simultaneously [2, 3] leading to the roughening. These cycles are comparable to the switching ON/OFF of electrolyzers and fuel cells and the resulting mound formation is eventually responsible for the degradation of the electrode making a large-scale introduction of renewable, hydrogen technology economically less feasible. The theoretically predicted mound shape nicely fits the experimental observation [4]. [1] M.J. Rost, L. Jacobse, and M.T.M. Koper, Nature Communications, 10, 5233, (2019) [2] L. Jacobse, Y.-F. Huang, M.T.M. Koper, and M.J. Rost, Nature Materials, 17 (3), 277, (2018). [3] Movie: https://youtu.be/xSpRcsgxq3Q [4] Movie: https://www.youtube.com/watch?v=xpN_mswrar8 Figure 1