Temperature Map Studies on Nearly Oxide-Free, Thin-Oxide and Standard-Oxide Cavities. ∗

A few nanometers of niobium oxide cover niobium in niobium cavities, prepared by standard treatments. Since the RF penetration depth is a few tens of nanometers, the niobium oxide and the metal-oxide interface may play role in RF losses of superconducting niobium. In order to understand the cause of phenomena such as the high field Qslope, medium field Q-slope, and residual resistance, it is important to distinguish the contributions of the niobium oxide and its interface to losses at medium and high fields. XPS and Auger studies have shown that it is possible to reduce significantly the thickness of the oxide layer by heating to 300 0 C - 400 0 C for a few hours in vacuum. Leaving the surface in the vacuum does not re-grow the oxide layer. Applying such treatment to a cavity one can reduce the niobium oxide and measure the superconducting RF properties of a nearly oxide-free cavity. Then via controllable air exposure one can re-grow oxide and investigate the change in properties as a function of exposure. We performed these experiments and report results of nearly oxide-free, thinoxide and standard-oxide cavities.