  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.
