  We consider a carpet of self-propelled particles at the liquid-gas interface
of a liquid film on a solid substrate. The particles excert an excess pressure
on the interface and also move along the interface while the swimming direction
performs rotational diffusion. We study the intricate influence of these
self-propelled insoluble surfactants on the stability of the film surface and
show that depending on the strength of in-surface rotational diffusion and the
absolute value of the in-surface swimming velocity several characteristic
instability modes can occur. In particular, rotational diffusion can either
stabilize the film or induce instabilities of different character.
