Degradation of superconducting properties in MgB2 films by exposure to water

The effect of water exposure on MgB2 is studied by submerging an 800 nm thi ck MgB2 film into de-ionized water at room temperature for 1 h, 4 h, 10 h, and 15 h, and by analysing the resulting material using scanning electron m icroscopy and resistance versus temperature measurements. It is clearly obs erved that the T-c(onset) of these films (obtained by an ex-situ reaction o f an e-beam evaporated boron layer) remains unchanged throughout this proce ss, indicating that at least a portion of the sample retains its original b ulk-like properties. The data is consistent with an interpretation in which a portion of the exposed film-likely to be the region closest to the subst rate-becomes superconducting only at similar to 25 K. It is possible that t his low-T-c region already exists in the as-prepared film, and we observe t hat its T-c coincides with that of MgB2 films obtained by annealing precurs or films prepared by pulsed laser deposition. Therefore the data presented here not only illustrates the degradation of MgB2 in water but also sheds l ight on the differences and similarities between films obtained via differe nt routes.