Comparative Transmission\nElectron Microscopy Study\nof ZnO Nanowire Growth by a Vapor–Solid Method and by Thermal\nOxidation during Joule Heating

The microstructure,\nmorphology, and structural quality\nof ZnO nanowires\ngrown by a vapor–solid (VS) mechanism and by oxidation during\nJoule heating of Zn wires by a current are compared using high-resolution\ntransmission electron microscopy (TEM) and scanning TEM (STEM). Growth\nof the nanowires by Joule heating is a rapid process, with times of\ntreatment in the range of seconds or minutes, whereas times for more\nconventional and widespread VS growth are normally in the range of\nhours at an elevated temperature. Nanowires grown by the two techniques\nare shown to have similar morphologies and to be single crystalline.\nThe incorporation of Tb dopants into both kinds of nanowires was investigated\nby using energy-dispersive X-ray spectroscopy and electron energy-loss\nspectroscopy. In nanowires grown by the VS method, Tb was found to\naggregate and form Tb oxide nanoparticles on parts of the nanowire\nsurfaces. In nanowires grown by Joule heating, no segregation of the\ndopants was observed. These results contribute to the understanding\nand development of inexpensive Joule synthesis methods for nanowires\nof ZnO and other oxides.