ZnO single crystal microtubes: Synthesis, growth mechanism, and geometric structure using direct microwave irradiation

ZnO single crystal microtubes have been successfully synthesized using direct microwave irradiation via the catalyst-free vapor–solid (V–S) process. Field emission scanning electron microscopy (FE-SEM) showed that ZnO single crystal microtubes exhibit a symmetrical 6-facet structure with an exact hexagonal hollow. ZnO single crystal microtubes have an average outer diameter of 100 µm and a length of over 300 µm, and the wall thickness ranges from 1 to 2 µm. X-ray diffraction (XRD) reveals a single high-intensity diffraction peak along the (101) direction, suggesting good crystallization of the synthesized ZnO single crystal microtubes. Single crystal diffraction (SCD) reveals the obvious polar nature of the ZnO single crystal microtube structure. The room-temperature photoluminescence (PL) spectrum shows an intense ultraviolet (UV) emission at 375.68 nm, with weak and broad visible light emissions in the range between 435 nm and 700 nm at a maximum peak of 588.66 nm.