Epitaxial-like Growth of Co₃O₄/ZnO Quasi-1D Nanocomposites

The development of quasi-1D Co₃O₄/ZnO nanocomposites by a two-step plasma enhanced-chemical vapor deposition (PE-CVD) process is presented. Arrays of ⟨001⟩ oriented ZnO nanorods were first grown on Si(100) and subsequently used as templates for the PE-CVD of Co₃O₄, whose amount was tailored as a function of deposition time. The obtained composites were thoroughly characterized by means of a multitechnique approach, involving field emission-scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDXS), micro-Raman and Fourier-transform infrared (FT-IR) spectroscopies, X-ray photoelectron and X-ray excited Auger electron spectroscopies (XPS, XE-AES), glancing incidence X-ray diffraction (GIXRD), and reflection high energy electron diffraction (RHEED). The use of moderate deposition temperatures (≤300 °C), together with the unique activation provided by nonequilibrium plasmas, prevented undesired solid-state reactions between the two oxides and promoted Co₃O₄ growth on the tips of vertically aligned ZnO nanostructures. In particular, the resulting quasi-1D Co₃O₄/ZnO composites were characterized by an interface epitaxial-like relationship, an important issue for the development of semiconductor-based functional nanosystems. Photoinduced hydrophilic (PH) and photocatalytic (PC) performances of the present nanocomposites were preliminarily investigated, showing attractive results toward the possible fabrication of advanced smart materials.