Strain Effect on Adatom Diffusion, Island Nucleation and Monolayer Growth on Metal and Oxide Surfaces

Multiphase thin films grown via pulsed laser deposition (PLD) have gained much interest owing to their unique anisotropic and strain-coupled properties in both vertical and horizontal directions. Due to lattice and elastic moduli mismatch, elastic strains arise in the multiphase material which impacts the growth processes of the film such as surface diffusion. For instance, it was hypothesized that tensile strain regions result in high energy activation barrier and favorable binding sites [1]. The impact of tensile strain fields due to array of misfit dislocations in the substrate yields to higher probability of nucleating islands [2,3]. Moreover, it is worth mentioning that diffusion and binding of adatoms depends on both the type of adatom and the atomic structure of the surface, with adatoms attracted or repelled from strained regions depending on the strain state [4]. Motivated by the growth of Au-CeO₂ multiphase system on SrTiO₃ [5], we use density functional theory (DFT) to understand the impact of strain on surface diffusion of Au adatom and CeO₂ admolecule on both the metal and oxide surfaces. We show that applying compressive or uniaxial can either favor or disfavor the binding of adatoms depending on the type of surface materials. In addition to that, applying strain induces distortion to the crystal lattice that favors the diffusion of one direction over another leading to anisotropic effect. On the larger scale, we utilize the DFT calculations to parameterize kinetic Monte Carlo (kMC) simulations where we demonstrate the impact of elastic strains on island nucleation and self-organization on different surfaces. The kMC model is approximated up to first order using tensorial notation. The results reveal that not only does strain impact the self-assembly process, but also the significance that utilizing elastic strains in multiphase systems can drive the phase-separation and patterning.<br/> <br/>[1] Z. Chen and N. Ghoniem. Biaxial strain effects on adatom surface diffusion on tungsten from first principles, <i>Phys Rev B</i> <b>88 </b>(2013) 35415<br/>[2] M. I. Larsson, K. Cho and B. M. Clemens. Surface diffusion mechanisms for strain-induced self-assembly, <i>Phys Rev B</i> <b>69 </b>(2004) 155426<br/>[3] R. F. Sabiryanov, M. I. Larsson, K. Cho and W. D. Nix and B. M. Clemens. Surface diffusion and growth of patterned nanostructures on strained surfaces, <i>Phys Rev B</i> <b>67 </b>(2003) 125412<br/> [4] R. V. Kukta, P. Liu, and D. Kouris. Adatoms and their relation to surface stress, <i>J Mech Phys Solids</i> <b>51</b> (2003) 1243-1266<br/>[5] J. Lu et al. Abnormal in-plane epitaxy and formation mechanism of vertically aligned Au nanopillars in self-assembled CeO₂-Au metamaterial systems. <i>Mater Horiz</i> <b>10</b> (2023) 3101