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In this work, a progressive oxidation method to fabricate double-walled nanotube structures is reported in detail. The approach is based on the electrodeposition of metallic iron nanowires, in porous alumina templates, followed by a selective chemical etching, nanoscale Kirkendall effect, a fast oxidation and out-diffusion of the metallic core structure during thermal annealing. To validate the formation mechanism of such core-shell structure, chemical composition and atomic structure were assessed. The resulting hematite nanotubes have a high degree of uniformity, along several microns, and a nanoscopic double-walled structure.<\/jats:p>","DOI":"10.1038\/s41598-019-47704-5","type":"journal-article","created":{"date-parts":[[2019,8,19]],"date-time":"2019-08-19T10:03:05Z","timestamp":1566208985000},"update-policy":"https:\/\/doi.org\/10.1007\/springer_crossmark_policy","source":"Crossref","is-referenced-by-count":18,"title":["Double-walled iron oxide nanotubes via selective chemical etching and Kirkendall process"],"prefix":"10.1038","volume":"9","author":[{"given":"Jo\u00e3o","family":"Azevedo","sequence":"first","affiliation":[]},{"given":"M. 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