  We study numerically the hydrodynamics of a self-propelled particle system,
consisting of spherical squirmers sedimented on a flat surface. We observe the
emergence of dynamic structures, due to the interplay of particle-particle and
particle-wall hydrodynamic interactions. At low coverages, our results
demonstrate the formation of small chiral spinners: two or three particles are
bound together via near-field hydrodynamic interactions and form a rotating
dimer or trimer respectively. The stability of the self-organised spinners can
be tuned by the strength of the sedimentation. Increasing the particle
concentration leads more interactions between particles and the spinners become
unstable. At higher area fractions we find that pusher particles can align
their swimming directions leading to a stable polar order and enhanced
motility. Further, we test the stability of the polar order in the presence of
a solid boundary. We observe the emergence of a particle vortex in a
cylindrical confinement.
