The effect of water exposure on MgB2 was studied by submerging an 800nm-thick MgB2 film into de-ionized water at room temperature for 1, 4, 10 and 15h, and by analyzing the resulting material using scanning electron microscopy and resistance versus temperature measurements. It was clearly observed that the TC,onset of these films (obtained by an ex-situ reaction of an e-beam evaporated B layer) remained unchanged throughout this process, indicating that at least a portion of the sample retains its original bulk-like properties. The data was consistent with an interpretation in which a portion of the exposed film - likely to be the region closest to the substrate - becomes superconducting only at ~ 25K. It was possible that this low-TC region already exists in the as-prepared film, and it was observed that its TC coincides with that of MgB2 films obtained by annealing precursor films prepared by pulsed laser deposition. Therefore the data presented here not only illustrates the degradation of MgB2 in water but also sheds light on the differences and similarities between films obtained via different routes.

Degradation of Superconducting Properties in MgB2 Films by Exposure to Water. H.Y.Zhai, H.M.Christen, L.Zhang, M.Paranthaman, P.H.Fleming, D.H.Lowndes: Superconductor Science and Technology, 2001, 14, 425-8