Constructing geometrically-ordered alumina nanoporous filters and alumina nanowire arrays by using ultrahigh voltage two step anodization

A simple ultrahigh voltage two-step anodization was developed to fabricate nanopore and nanowire arrays which can be utilized in various applications like water purification filter technology. Investigation of the electrolyte concentration effect on controlling the morphology and geometry of the alumina nanopore and nanowire (ANW) arrays has been done. The anodization was carried out in H2C2O4/H3PO4 mixture at about 0 degrees C to reach the best ordered nanopores array. In hard anodization step, the current density showed a peak shape profile so that its maximum was directly depended on the H3PO4 concentration. The SEM images of the arrays were studied by image histogram and fast Fourier transform (FFT). The model curves demonstrated direct dependency of the nanopores ordering on electrolyte concentration. The most ordered array was achieved by utilizing 0.3 M H2C2O4 and 0.35 M H3PO4. The SEM images showed that the pores became wider by etching the nanopores in an acidic solution. In addition, fast fabrication of nanowire arrays was achieved by managing the anodization process at 30 degrees C in a short time. The ANWs were obtained from nanopores etching through the anodization, without an extra etching step requirement. The studies on SEM images demonstrated succeeding high ordered ANWs bundle.