  A method to treat the surface of Nb is described which potentially can
improve the performance of superconducting RF cavities. We present tunneling
and x-ray photoemission spectroscopy (XPS) measurements at the surface of
cavity-grade niobium samples coated with a 3 nm alumina overlayer deposited by
Atomic Layer Deposition (ALD). The coated samples baked in ultra high vacuum
(UHV) at low temperature reveal at first degraded superconducting surface.
However, at temperatures above 450C, the tunneling conductance curves show
significant improvements of the superconducting density of states (DOS)
compared with untreated surfaces.
