= Solution
<Zinc blende> and <wurtzite> differ in their stacking of tetrahedrally bonded bilayers: an ideal cubic sequence is ABCABC, while the hexagonal sequence is ABAB. During <vapor–liquid–solid growth>, each new interfacial nucleus can choose between continuing the existing sequence and changing it.
\b[The selected phase can be the one with the smaller nucleation barrier, rather than the lower bulk free energy alone.] A nucleus at the droplet–wire–vapour triple line has edge and interfacial energies different from a nucleus fully inside the liquid–solid interface. Schematically, its free energy combines a favourable chemical-potential term with new edge/interface costs and, when appropriate, a stacking penalty. Supersaturation changes the relative importance of these terms; the droplet shape and contact angle change which nucleation sites are available.
Control is therefore possible through temperature, III/V supply ratio, precursor fluxes, catalyst composition, droplet volume/contact angle and wire diameter. Monitoring growth rather than only inspecting cooled specimens helps determine which parameter actually changes the interface. A nucleation model for Au-catalysed III–V wires explicitly showed how triple-line nucleation can favour wurtzite under suitable interface energies and supersaturation.<Why does wurtzite form in nanowires of III-V zinc blende semiconductors by Frank Glas and others>[2007, competing phase nucleation at the triple line]{ref} There is no universal rule that one phase always corresponds to the larger temperature or smaller diameter regardless of catalyst and interface geometry.
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