Morphology of Amorphous Layers Ballistically Deposited on a Planar Substrate

TL;DR

This paper presents a numerical simulation study of spherical particle deposition on a planar surface, revealing a loosely layered, sparse structure with specific contact statistics, modeled by chain formation and power-law density approach.

Contribution

It introduces a model of ballistic particle deposition that explains the morphology and contact statistics of amorphous layers formed on planar substrates.

Findings

Deposit has about 15% space-filling fraction.

Average contact number per particle is approximately 2.

Deposit structure results from screening and branching effects.

Abstract

We report numerical simulation of the deposition of spherical particles on a planar surface, by ballistic, straight-line trajectory transport, and assuming irreversible adhesion on contact with the surface or previously deposited particles. Our data indicate that the deposit formed has a loosely layered structure within few diameters from the surface. This structure can be explained by a model of growth via chain formation. Away from the surface we found evidence of a monotonic, power-law approach to the bulk density. Both density and contact-statistics results suggest that the deposit formed is sparse: the space-filling fraction is about 15%, and the average number of contacts is 2. The morphology of the deposit both near the surface and in the bulk seems to be a result of competition of screening and branching; nearly half of all the spheres are either single-contact dangling ends, or branching nodes with more than two contacts.