We have studied electron transport in Sn-Ni-Sn structures, in which the Ni
had the form of a narrow (similar to 400 Angstrom wide) wire. The behaviour
is very sensitive to the quality of the Ni-Sn interface. With a clean inte
rface, there appears to be a significant proximity effect in the Ni, and th
e results imply an unexpectedly long proximity length. However, when an oxi
de layer is present at the Sn-Ni interface, the effective resistance of the
Ni increases as the temperature is reduced below the critical temperature,
T-c, of the Sn. It does not appear that these observations can be explaine
d by current theories.