The Tc -mapping method using low temperature scanning electron microscopy (LTSEM) has been developed to study the spatial distribution of the critical temperature in high temperature superconducting (HTSC) films with a spatial resolution approaching 2 μm. To achieve so high a spatial resolution, a numerical deconvolution method was applied that eliminated distorting effects associated with the thermal diffusion and with the contribution from the absorbed beam current. The Tc -mapping method was used to investigate modification by water of YBa2Cu3O7-x films grown on (100) MgO and (110) LaAIO3 substrates. The rate of modification of a [110]-oriented YBa2Cu3O7-x/LaAIO3 film is found to be 40 times that of a c-axis oriented YBa2Cu3O7-x/MgO epitaxial film. It is argued that water-initiated modification of the films results from penetration of hydrogen into the films, rather than from out-diffusion of oxygen
