Microstructural characterization and formation mechanism of 21° top facets of ZnO-based nanowall structures

This study reports the microstructural characterization and formation mechanism of the 21° top facets of ZnO-based nanowall structures. The ZnO-based nanowall structures reported previously by many other research groups have {112¯0} planes as major planes and top facets with a specific angle in common, irrespective of the growth techniques and growth conditions. These nanowalls were found to exist between two adjacent nanowires with a c  -axis preferred orientation, and the atoms at the junction of the nanowalls and nanowires perfectly coincided with each other at an atomic level, without any defects. The top facets of the nanowalls showed periodically stepped surfaces and were identified as {011¯5} planes, which were perpendicular to the {112¯0} major planes. On the basis of the microstructural characterization of the synthesized ZnO-based nanowall structures, the formation mechanism and atomic structure model of the 21° top facets of the nanowall structures are proposed.