Z.N. Urgessa

Low temperature near band edge recombination dynamics in ZnO nanorods

The recombination dynamics of neutral donor bound excitons (DoX: I4, I6/6a) and near band edge defect-related emission in solution grown ZnO nanorods are investigated using steady state and time-resolved photoluminescence (PL) measurements. The effects of annealing are also studied. Low temperature steady state PL shows a systematic removal of the I4 line after annealing at 450 °C and the subsequent domination of I6a in these PL spectra. Additionally, the time decay of the I4, I6/6a, free exciton (FX), and basal plane stacking fault-related (BSF) PL transitions are studied as a function of annealing temperature. For the various annealing temperatures studied, the PL decay is described by a bi-exponential profile with a fast component (contribution from the surface) and slow component (related to bulk recombination). The fast component dominates in the case of as-grown and low temperature annealed samples (anneal temperatures up to 300 °C), suggesting the presence of surface adsorbed impurities. For sample...

Comprehensive study of ZnO nanostructures grown using chemical bath deposition: from growth to application

ZnO nanostructures were grown using a simple and environmentally friendly chemical bath deposition technique on pre-treated p-type silicon substrate at temperatures below 100°C. The effects of growth parameters like seed layer density, growth time, growth temperature, precursor concentration and annealing temperature on the structural, morphological, electrical and optical properties of ZnO nanorods were systematically studied using field emission scanning electron microscopy, X-ray diffraction, photoluminescence spectroscopy and current-voltage measurements. A variety of architectures is demonstrated, ranging from single crystalline nanoparticles and c-axis orientated nanorods to highly compact crystalline thin films. Post-growth annealing at different temperatures profoundly affects the optical properties of the nanorods by, for example, reducing hydrogen- and intrinsic defect-related emission. The rectifying properties of the ZnO/Si heterojunction are discussed.

Formation mechanism of the rutile-phase of TiO2 nanorods on Ti foil substrate by gel-calcination method

A formation mechanism that leads to the synthesis of rutile-phase TiO2 nanorods at high temperatures on Ti foil by NaOH-based gel-calcination is discussed based on a series of experimental investigations. TiO2 nanostructures are prepared on Ti foil following two steps, namely gelation and calcination. It is shown that the use of an alkali-based solution during gelation, such as NaOH and KOH, leads to the formation of faceted TiO2 nanorods upon calcination at high temperature (~800 °C). When an acidic solution that does not contain an alkali element, such as H2O2, is used during gelation, the shape of the nanostructures upon calcination at high temperature does not display the faceted nanorod shape. The following formation mechanism is suggested: the high temperature calcination of the Na based amorphous network of dendritic structures (formed on the Ti surface during a 24-h soak in NaOH solution) converts it into Na-titanate in the shape of nanorods. This in turn converts into nanorods of rutile-phase TiO2 when Na evaporates in the form of an oxide.Graphical Abstract