For the Fe-based superconductor Fe1+yTe1-xSx, superconductivity is induced by annealing treatment in oxygen atmosphere, whereas as-grown samples do not show superconductivity. We investigated the sample-size dependence of O2-annealing effects in Fe1.01Te0.91S0.09. The annealing conditions were fixed to 1 atm, 200°C, and 2 h. We carried out magnetic susceptibility and specific heat measurements in order to evaluate the superconducting volume fraction. We found that Fe1+yTe1-xSx has an optimal size for the induction of bulk superconductivity by O2 annealing. Our results indicate that O2 annealing is probably effective near the surface of samples over a length of a few tens of micro meters.
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