AgI/Ag heterojunction nanowires: Facile electrochemical synthesis, photoluminescence, and enhanced ionic conductivity

The construction of an electronic-conductor/ionic-conductor heterojunction in a well-defined nanostructure is the basis of studying interfacial and bulk transport and the reactions of ions and electrons at the nanoscale level. An ionic-conductor/metal (AgI/Ag) beterostructured nanowire array is easily fabricated by a template-confined, step-electrochemical technique. The structural and morphological evolution of the AgI/Ag heterostructure before and after its release from the anodic aluminum oxide (AAO) membrane is characterized by scanning electron microscopy, X-ray diffraction, and optical spectroscopy. The structural disordering of released AgI is suggested by the appearance of a broad photoluminescence emission band at longer wavelengths and a short-range-order-like Raman peak. The ionic conductivity of the AgI nanowire embedded inside the insulating AAO membrane is measured as being on the order of 10(-3) S cm(-1), which is an enhancement by two to three orders of magnitude compared with that of bulk polycrystalline AgI at room temperature. This electrochemical method could be useful in fabricating other pure and mixed ionic conductors in heterojunction nanostructures.