Sawtooth Faceting in Rutile Nanowires

Sawtooth faceting, with a diameter-dependent period, is pervasively observed in many Si, III-V, and II-VI nanowires during vapor-phase growth. This can be linked to an oscillation in surface energies, which are influenced by many factors such as crystal anisotropy, surface decoration, and twinning. Without the presence of surface decoration and planar defects, TiO₂ rutile nanowires, axially oriented along a low-symmetry axis of ⟨110⟩, are promising to decouple the effect of crystal anisotropy from other factors. In this work, we synthesized ⟨110⟩ rutile nanowires, which exhibit complex periodic faceting consisting of {101} and {11̅0} facets. In addition to the expected linear width dependence, rutile nanowires, with the same width but different outward-inclined shapes, maintain the same period of their sawtooth faceting, as measured from TEM micrographs. In spite of different surface energy oscillations caused by different shapes, identical nucleation sites, which become energetically favorable during sawtooth growth, are predicted using thermodynamic models for nanowires with different shapes. This finding provides new insights into the morphological control of nanowires.