These last few years a great effort has been made to understand the mechanisms of powder formation in silane discharges. It is now well established that powders are negatively charged and thus confined in the plasma. Therefore, one does not expect powders to contribute to the deposition, unless the plasma is switched off. We present here experimental evidence for the deposition of nanoparticles, even in the case of a continuous discharge. Experimental conditions for nanoparticle formation while avoiding powder formation have been determined from light-scattering and transmission electron microscopy measurements. Nanoparticle deposition has been studied by in situ ellipsometry in silane-argon discharges. From a comparison of the growth kinetics and the optical properties of films obtained under continuous and modulated discharges we conclude that nanoparticle deposition can take place even when the discharge is on. The implications of these discoveries on the properties of hydrogenated amorphous silicon are discussed in the framework of previous studies where we showed that low defect density and well relaxed films are deposited under conditions where nanoparticles and powders are formed in the discharge. The improved properties in these films are attributed to the incorporation of nanoparticles.