Deep Surface Trap States at ZnO Nanorods Arrays

ABSTRACTDeep surface trap states present in hydrothermally grown ZnO nanorod (NR) arrays are monitored by photoelectrochemical and impedance spectroscopy. NR arrays were grown on a thin compact ZnO film deposited by pulsed laser deposition. Photocurrent responses upon square-wave illumination and lock-in detection of the as-grown NR arrays in the presence of Na2SO3 at pH 10 were characterized by a complex potential dependence indicating the presence of deep trap states. At a given frequency of light perturbation, the photocurrent amplitude increases as the potential bias is shifted towards values more positive than the flat band potential. Increasing the potential further than 0.8 V positive to the flat band potential leads to a decrease in the photocurrent amplitude. The potential of maximum photocurrent amplitude overlaps with a sharp decrease in the interfacial capacitance. The dependence of the photocurrent amplitude on bias potential strongly suggests the presence of deep electron trap states. The effect of the deep trap states are minimized by annealing of the NR arrays in air at 340° C.</jats:p

Modulating the Reactivity of Electrode Surfaces by Electrostatic Assembly of Metal Nanoparticles and Quantum Dots

Charge transport phenomena in opto-electronic devices featuring functional polymers and nanostructured materials critically depend on the electronic communication between the building blocks and the metal contacts. The generation of ordered multilayer structures at electrode surfaces is often a key requirement to avoid electrically isolated (inactive) areas in the devices. This issue is particularly crucial in hybrid photovoltaic, light emitting and electrochromic systems. In the present contribution, the properties of electrode surfaces modified by electrostatic layer-by-layer methods are highlighted as a versatile approach for generating two- and three-dimensional assemblies of nanostructures. The connectivity between the nanoparticles and the electrode surface is probed by a variety of techniques including Kelvin probe, electrostatic force microscopy and electrochemical methods. The main characteristics of electrode surfaces modified by electrostatic self-assembly are illustrated with several examples involving metal nanostructures and CdTe quantum dots. ? Schweizerische Chemische Gesellschaft