Electron tomography and high-resolution transmission electron microscopy were used to characterize the unique 3-dimensional (3D) structures of twinned Zn3P2 (tetragonal) and InAs (zinc blende) nanowires synthesized by the vapor transport method. The Zn3P2 nanowires adopt a unique superlattice structure that consists of twinned octahedral slice segments having alternating orientations along the axial [111] direction of a pseudocubic unit cell. The apices of the octahedral slice segment are indexed as six equivalent <112> directions at the [111] zone axis. At each 30 degrees turn, the straight and zigzagged morphologies appear repeatedly at the <112> and <011> zone axes, respectively. The 3D structure of the twinned Zn3P2 nanowires is virtually the same as that of the twinned InAs nanowires. In addition, we analyzed the 3D structure of zigzagged CdO (rock salt) nanowires and found that they include hexahedral segments, whose six apices are matched to the <011> directions, linked along the [111] axial direction. We also analyzed the unique 3D structure of rutile TiO2 (tetragonal) nanobelts; at each 90 degree turn, the straight morphology appears repeatedly, while the in-between twisted form appears at the [011] zone axis. We suggest that the TiO2 nanobelts consist of twinned octahedral slices whose six apices are indexed by the <011>/<001> directions with the axial [010] direction.

High-density TiO2-CdS and ZnO-CdS core-shell nanocable arrays were synthesized on large-area Ti substrates. The CdS layers were deposited on the pre-grown vertically-aligned TiO2 (rutile) and ZnO nanowire arrays, with a controlled thickness (10~50 nm), using the vapor transport method. The ZnO-CdS nanocables consisted of single-crystalline wurtzite CdS shells whose [001] direction was aligned along the [001] wire axis of the wurtzite ZnO core, which is distinctive from the polycrystalline shell of the TiO2-CdS nanocables. We fabricated the photoelectrochemical cell using the ZnO-CdS photoelectrode exhibits much more efficient hydrogen generation than that using the TiO2-CdS one.