Self-organized ZnO microcombs with cuboid nanobranches by simple thermal evaporation

Microscale wide and millimeters long comblike ZnO single crystals with well-aligned cuboid nanobranches were fabricated using a double-tube simple thermal evaporation method without the presence of a catalyst at 950 degrees C. X-ray diffraction and Raman spectra revealed that the as-grown products had a wurtzite crystal structure. The morphology and microstructure analyses of ZnO microcombs were performed by field emission scanning electron microscopy and transmission electron microscopy. The ZnO microcombs were about 1-3 millimeters in length, with branching rods about 40 mu m in length and 500-800 nm in width. Selected area electron diffraction confirmed that the branching rods and ribbon stems grew along the [0001] and [01 (1) over bar0] in each direction, respectively. Photoluminescence measurement of the microcombs showed a weak UV emission band and a broad yellow-green emission band centered at 395 and 530 nm, respectively. A possible growth mechanism based on different preferred growth orientations of ribbon stems and branching rods was also proposed.