Li-doped ZnO nanorods with single-crystal quality - non-classical crystallization and self-assembly into mesoporous materials

The exploitation of semiconductors is of utmost importance to existing and forthcoming technologies. Some have even argued that in analogy to the ‘Copper Age’ following the ‘Stone Age’, we are currently living in the Semiconductor Age. For sure, silicon is the semiconductor which is used the most in a technological context (e.g. microelectronics). However, there are various applications for which silicon is not suitable due to either its relatively narrow band-gap or its indirect band-structure. Therefore, there is large interest in wide, direct gap semiconductors like III/V compounds, for instance gallium nitride (GaN), or II/VI compounds such as zinc oxide (ZnO). Furthermore, for silicon, it is well documented that the pure compound itself is only of very limited use. Functional devices like photovoltaic cells require pand n-doped Si. Interestingly, the exploitation of doping to control the properties of ceramic semiconductor nanostructures still stands at the beginning. Most nanomaterials presented in the literature consist of the pure semiconductor, or unintentional doping with impurities has occurred. Zinc oxide, one of the most important binary semiconductors in current research, is interesting because of its multifunctional character with applications in various fields such as optoelectronics (e.g. photovoltaics, transparent electronics), cosmetics (UV protection), sensor technology (gas sensors, bio sensors) or catalysis (methanol synthesis). One-dimensional ZnO nanostructures have also attracted significant attention. Despite much recent research, important challenges remain. ZnO is intrinsically n-doped due to its tendency to form native point defects and due to the presence of residual shallow donors such as interstitial hydrogen or of Al, Ga, or In on Zn lattice sites. Major efforts have been undertaken to achieve p-doping of ZnO via partial substitution of zinc by lithium or, alternatively, of oxygen by nitrogen. The desired p-doping has often been found to be compensated by unintentional n-doping resulting from dopants being located on interstitial sites in the lattice. The development of reliable methods for the preparation of Li–ZnO colloidal particles, ultimately of nanorods, with precise lattice site control of the dopants, would thus represent a major advance. Particular importance in this context is attributed to routes leading to colloidal ZnO nanorods. A common way to prepare ZnO is to start from an aqueous solution of a Zn salt (e.g. zinc acetate), followed by the precipitation of zinc–oxo–hydroxo University of Konstanz, Universitaetsstr. 10, 78464 Konstanz, Germany.