Microwave irradiation assisted rapid growth of ZnO nanorods over metal coated/electrically conducting substrate

In-spite of intense research in the growth of ZnO over the years, the direct crystallization of ZnO on a metal coated/electrically conducting substrate by a solution growth process has not been carried out. We report one pot, low temperature (≤100 °C) and rapid growth (5 min) of ZnO nanorods over an electrically conducting substrate by using microwave irradiation assisted thin film deposition in a liquid medium without the use of any seed layer. High density (2 × 10⁹/cm²), c-axis oriented, uniform and continuous ZnO nanorod films are grown over Cr/Si [chromium coated Si(1 0 0)] and ITO/glass (indium tin oxide coated glass) substrates whereas aluminium (Al) and gold (Au) coated Si yield non uniform film with mixed texture. Microwave irradiation for 5 min ensures strongly oriented growth of ZnO over Cr/Si and ITO/glass and mixed texture for semiconducting substrates (Si/Ge). The initial nucleation of ZnO nanorods may be due to the formation of thin amorphous oxide (Cr₂O₃) layer over Cr film, which subsequently changes to hydroxides (CrOH₂, CrOH₃) in contact with water.