We report on one-step growth of superconducting SmFeAs(O,F) films without post-growth fluorine diffusion. One-step growth is a prerequisite for multilayer deposition, which is required for fabricating sandwich-type Josephson junctions; however, it has not been achieved because of a lack of a suitable fluorine source. We found that FeF2, a ‘soft’ fluoride, decomposes at relatively low temperatures (∼650 °C) and supplies fluorine as well as Fe to films. The use of FeF2 has enabled us to perform reproducible growth of SmFeAs(O,F) films with a systematic change of the film’s properties by varying growth parameters. Now, single-phase single-crystalline SmFeAs(O,F) films with
are routinely prepared. Furthermore, the c-axis lattice parameter of the films are varied in a systematic manner with the FeF2 deposition rate, indicating that the F doping level seems to be controllable. The comparison of one-step growth and our previous two-step growth demonstrates that a more homogeneous F concentration is achieved by one-step growth, whereas higher F concentration is achieved by two-step growth.
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