Surface and Bulk Properties of Deposits Grown with a Bidisperse Ballistic Deposition Model

TL;DR

This study investigates the surface roughness and internal porosity of deposits formed via a bidisperse ballistic deposition model, revealing KPZ scaling on the surface and a connection between surface growth and bulk properties.

Contribution

It introduces a scaling theory linking surface roughness and bulk porosity in bidisperse ballistic deposits, highlighting universality and the effects of particle size ratio.

Findings

Surface exhibits KPZ scaling regardless of particle flux ratio.

Porosity scales as F^{1/2} for small F, connecting surface and bulk properties.

Deposits percolate down to low flux ratios, with internal surface fractal dimension ~2.9.

Abstract

We study roughness scaling of the outer surface and the internal porous structure of deposits generated with the three-dimensional bidisperse ballistic deposition (BBD), in which particles of two sizes are randomly deposited. Systematic extrapolation of roughness and dynamical exponents and the comparison of roughness distributions indicate that the top surface has Kardar-Parisi-Zhang scaling for any ratio F of the flux between large and small particles. A scaling theory predicts the characteristic time of the crossover from random to correlated growth in BBD and provides relations between the amplitudes of roughness scaling and F in the KPZ regime. The porosity of the deposits monotonically increases with F and scales as F^{1/2} for small F, which is also explained by the scaling approach and illustrates the possibility of connecting surface growth rules and bulk properties. The suppression of relaxation mechanisms in BBD enhances the connectivity of the deposits when compared to other ballisticlike models, so that they percolate down to F~0.05. The fractal dimension of the internal surface of the percolating deposits is D_F~2.9, which is very close to the values in other ballisticlike models and suggests universality among these systems.