title: Chemical protection of ZnO nanorods at ultralow pH To form a hierarchical BiFeO3/ZnO core-shell structure.
abstract: ZnO is an interesting material for photoactive and optoelectronic devices because of the wide range of available nanostructures and advantageous semiconducting properties. However, a significant drawback of ZnO is the low stability in high or low pH solutions. This has limited the development of ZnO core-shell materials for use in Z-scheme systems or photovoltaics, where any secondary phase is produced using chemical solution processing at low or high pH. Here, we show a simple process to produce an organic capping layer of 3-aminopropyltriethoxysilane that can successfully stabilize nanostructured ZnO for processing below pH 1. We demonstrate that this process can be used to produce a ZnO-BiFeO3 (BFO) core-shell structure by a sol-gel process. Using a range of physical and analytical techniques, we show that BFO is highly crystalline and produces a conformal coating with a thickness of 2.5 nm. X-ray photoelectron spectroscopy and X-ray diffraction confirm the phase and expected chemical composition of BFO. Finally we are able to demonstrate that diodes produced using the ZnO-BFO core-shell structure have improved performance with a rectification ratio at ±3 V of 2800 because of the reduction in reverse current typically associated with surface recombination on ZnO. Our process opens a route to producing a range of hitherto prohibited ZnO core-shell structures that may have applications ranging from photovoltaic devices to core-shell photocatalysts.
authors.affiliation: Materials Research Institute, School of Engineering and Materials, Queen Mary University of London , London E1 4NS, United Kingdom.
authors.forename: Leonard
authors.initials: L
authors.lastname: Loh
authors.forename: Joe
authors.initials: J
authors.lastname: Briscoe
authors.forename: Steve
authors.initials: S
authors.lastname: Dunn
keywords: APTES; BFO; ZnO; chemical protection; nanostructure