  This tutorial presents in the first part the requirement for the surface
preparation of RF Niobium cavities and its justification in term s of physical
origin of limitation (e.g. cleanliness and field emission, influence of the
surface treatments, morphology and surface damage, etc.). in the second part we
discuss the different models describing the ultimate limits of SRF cavities,
and present one of the possible ways to overcome Niobium monopoly toward higher
performances.
