Communication: The structure and stability of self-assembled 1D superlattices based on deuterated poly(p-phenylenevinylene) (PPV) and non-deuterated spacer layers is investigated by neutron reflectivity This allows, in particular, the interlayer penetration to be accurately determined-an important parameter to be able to control and minimize for the fabrication of multilayer devices. It is demonstrated that the successful preparation of superlattices largely depends on drying and removal of excess polyelectrolyte after each deposition cycle by spinning the sample.