Critical Role of Screw Dislocation in the Growth of Co(OH)₂ Nanowires as Intermediates for Co₃O₄ Nanowire Growth

In our prior studies, we reported the growth of Co 3 O 4 nanowire arrays via the ammonia-evaporation-induced growth in solution and their promising applications in a Li-ion battery and oxygen evolution. Although we had identified that the growth of Co 3 O 4 nanowire went through the β-Co(OH) 2 intermediate, the growth mechanism of Co(OH) 2 nanowire was still elusive. The problem seemed to be rooted in its layered brucite crystal structure, which was not previously known to grow one-dimensionally (1D) perpendicular to the layers. In this paper, we present our recent discovery that axial screw dislocation is responsible for such longitudinal growth. Through bright-field transmission electron microscope (TEM) characterizations, the screw dislocation was directly observed as a dark-contrasted line along Co(OH) 2 nanowires. Emergent spiral growth steps provide active sites for immediate adsorption of incoming molecules, resulting in a fast spiral advance rate along the c -axis of the brucite crystal. This study shows a new example of the screw-dislocation driven growth of 1D nanostructures.