Interfacial Natures and Controlling Morphology of Co Oxide Nanocrystal Structures by Adding Spectator Ni Ions

Abstract

Cobalt oxide nanostructure materials have been prepared by adding several concentrations of spectator Ni ions in solution, and analyzed by electron microscopy, X-day diffraction, calorimetry/thermogravimetric analysis, UV-vis absorption, Raman, and X-ray photoelectron spectroscopy. The electron microscopy results show that the morphology of the nanostructures is dramatically altered by changing the concentration of spectator ions. The bulk XRD patterns of <TEX>$350^{\circ}C$</TEX>-annealed samples indicate that the structure of the cobalt oxide is all of cubic Fd-3m <TEX>$Co_3O_4$</TEX>, and show that the major XRD peaks shift slightly with the concentration of Ni ions. In Raman spectroscopy, we can confirm the XRD data through a more obvious change in peak position, broadness, and intensity. For the un-sputtered samples in the XPS measurement process, the XPS peaks of Co 2p and O 1s for the samples prepared without Ni ions exhibit higher binding energies than those for the sample prepared with Ni ions. Upon <TEX>$Ar^+$</TEX> ion sputtering, we found <TEX>$Co_3O_4$</TEX> reduces to CoO, on the basis of XPS data. Our study could be further applied to controlling morphology and surface oxidation state.