J. Grabowska

Observation of epitaxially ordered twinned zinc aluminate “nanoblades” on c-sapphire

We report the observation of a novel nanostructured growth mode of the ceramic spinel zinc aluminate grown on c-sapphire in the form of epitaxially ordered twinned crystallites with pronounced vertically aligned “nanoblades” on top of these crystallites. The nanostructures are formed on bare c-sapphire substrates using a vapour phase transport method. Electron microscopy images reveal the nanostructure morphology and dimensions and allow direct and indirect observation of the twin boundary location in a number of samples. The nanoblade structure with sharply rising sidewalls gives rise to a distinctive bright contrast in secondary electron images in scanning electron microscopy measurements.

Morphological control of ZnO nanostructures grown on silicon

We report growth of ZnO nanostructures on Au-coated Si substrates using vapor phase transport in the temperature range from 800°C to 1150°C. Nanostructures grown at 800°C are rod-like with diameters of ~ 200 nm. Growth at higher temperature shows a more complex behaviour with 2-D structures connecting 1-D nanorods at intermediate temperatures and 3-D growth at the highest temperatures. Our work indicates that it may be possible to systematically control the growth mode and morphology of ZnO nanostructures by tuning the growth temperature.

Spectroscopic Study of the Properties of Chemically Modified ZnO Nanowires

A heterogeneous system composed of zinc oxide nanorods and ruthenium bipyridyl complex dye molecules is described. The photophysical and spectroscopic properties of the system are reported. It has been found that the ruthenium complex binds well to the zinc oxide nanorods and exhibits strong emission properties characteristic of ruthenium complexes. Photoluminescence and emission studies suggest that the ruthenium dye influences the emission and lifetime of the zinc oxide.

Laterally and vertically grown ZnO nanostructures on sapphire

Lateral growth of ZnO nanowall arrays with subsequent growth of vertical nanowires using a two-step vapour phase transport method on a-plane sapphire are reported. X-ray diffraction and scanning electron microscopy data show that the nanostructures are aligned with c-axis normal to the substrate. Photoluminescence data demonstrate the exceptionally high optical quality of these structures, with intense emission and narrow bound exciton linewidths. We observe high energy excitonic emission at low temperatures close to the band-edge which we assign to the surface exciton in ZnO at ~3.366 eV. This assignment is consistent with the large surface to volume ratio of the nanowire systems and indicates that this large ratio has a significant effect on the luminescence even at low temperatures. The band-edge intensity decays rapidly with increasing temperature compared to bulk single crystal material, indicating a strong temperature-activated non-radiative mechanism peculiar to the nanostructures. No evidence is seen of the free exciton emission due to exciton delocalisation in the nanostructures with increased temperature, unlike the behaviour in bulk material. The use of such nanostructures in room temperature optoelectronic devices appears to be dependent on the control or elimination of such surface effects.