Effects of Adsorbate Diffusion and Edges in a Transition from Particle to Dendritic Morphology during Silver Electrodeposition

Abstract

During silver electrodeposition on Au nanoparticle (NP)-covered highly oriented pyrolitic graphite, a transition from an initial growth of microsized particles to the growth of dendrites with pine tree shape (nanotrees) is observed, which is an advancement for material growth with hierarchical surface roughness. Using kinetic Monte Carlo simulations of an electrodeposition model, those results are explained by the interplay of diffusive cation flux in the electrolyte and relaxation of adsorbed atoms by diffusion on quenched crystal surfaces. First, simulations on NP-patterned substrates show the initial growth of faceted silver particles, followed by the growth of nanotrees with shapes similar to the experiments. Next, simulations on electrodes with large prebuilt particles explain the preferential nanotree growth at corners and edges as a tip effect. Simulations on wide flat electrodes relate the nanotree width with two model parameters describing surface diffusion of silver atoms: maximal number of random hops (G) and probability of hop per neighbor (P). Finally, simulations with small electrode seeds confirm the transition from initially compact particles to the nucleation of nanotrees and provide estimates of the transition sizes as a function of those parameters. The simulated compact and dendritic deposits show dominant (111) surface orientation, as observed in experiments. Extrapolations of simulation results to match microparticle and nanotree sizes lead to G = 4 × 1011 and P = 0.03, suggesting to interpret those sizes as diffusion lengths on the growing surfaces and giving diffusion coefficients 2 to 3 × 10–13 m2/s for deposited silver atoms. These results may motivate studies to relate diffusion coefficients with atomic-scale interactions.

Secondary Nucleation and Unstable Roughening in Fe Layers Electrodeposited on Si

“…Previous studies of this model with G s = G f show that the lateral sizes of correlated structures (including dendrite sizes) scale approximately as G f 0.4 . , Thus, we expect that the Fe grain sizes would be produced only in simulations with G f ∼ 10 6 (and with an appropriate lattice structure). Extending the interpretation of ref , this value of G f corresponds to a diffusion length ∼300 nm for an adatom on a terrace of the film surface.…”

“…These features reveal an unstable roughening at the longest times. Due to the preferential cation reduction at the most protuberant points of the deposit, the instability develops when the surface fluctuations become large enough that the surface relaxation is unable to redistribute the deposited mass uniformly. , The correlation length in the unstable regime slowly increases (Figure b). These features at longer times are in qualitative agreement with the experiments.…”

“…Cumulatively, these factors would require ∼10 3 times longer simulations. Similar limitations were observed in simulations of silver electrodeposition, but reliable extrapolations of G f were possible.…”

“…As the density of secondary grains increases, the average grain size at the film surface decreases, leading to a sharp decrease in the correlation length shown in Figure 6b. However, the secondary grains weakly affect the global roughness, which is related to the largest surface fluctuations 49 (reminiscent of the initial islands). For these reasons, the global roughness oscillations are properly described by the model.…”

“…Growth Des. XXXX, XXX, XXX−XXX electrodeposition,49 but reliable extrapolations of G f were possible.…”