Topotactic thermal oxidation of Sn nanowires: Intermediate suboxides and core-shell metastable structures

An easily generalizable method is reported for converting metal nanowires topotactically to their stoichiometric oxides. Because many such metal oxides are the active semiconductor elements in sensors, this method is potentially useful in preparing nanowire-based sensor elements. The process is illustrated by converting Sn nanowires fabricated electrochemically in porous alumina templates to SnO2 in a manner that preserves the wire's nanostructure. The kinetically controlled oxidation process, which is initially fed by molten tin at the nanowire's core, gives rise to a number of distinct, coaxial core-shell metastable phases. The process can easily be extended to fabricate free-standing arrays of parallel metal oxide nanowires with possible sensor and optoelectronic applications that are structurally compatible with planar technologies.