PUMA
Istituto dei materiali per l'elettronica ed il magnetismo     
Villani M., Zanotti L., Lazzarini L., Calestani D., Zha M., Zappettini A. Synthesis of cadmium sulfide sensitized ZnO nanostructures. In: ICG 2010 - Italian Crystal Growth - Progress in Functional Materials (Parma, 18-19/09 2010).
 
 
Abstract
(English)
Large band gap oxide semiconductors, like TiO2 and ZnO, are known to have promising properties for solid state devices, such as photoconductive, solar and electroluminescent cells as well as for photo-catalytic systems [1]. Nevertheless there are some drawbacks associated with their use such as fast carrier recombination and UV band edge absorption threshold that does not allow the utilization of visible light. One of the main approaches to overcome these particular limitations involves the coupling of TiO2/ZnO nanostructures with other semiconductors, with lower band gap, called "sensitizer". This is the case of ZnO nanostructures combined with a photoactive layer that extend the absorption threshold to the visible region and the photo-generated electrons are quickly transferred from the layer into to the lower lying conduction band of ZnO, thus limiting direct recombination effects. The present work shows the possibility to sensitize ZnO nanostructures, and in the specific, "tetrapods" (TP), with nanoparticles of cadmium sulfide using a modified chemical bath deposition (CBD) process. The typical synthesis route to produce chalcogenide nanocrystals requires alkaline environment for the formation metal hydroxide clusters via basic hydrolysis [2]. This route cannot be followed when ZnO nanostructures are used because of their poor chemical stability. A different synthesis route was defined using an organic polar aprotic solvent (dimethylformamide) that allows both the suspension of ZnO nanoparticles and solvation of cadmium and sulfur precursor salts. In order to promote the heterogeneous nucleation of CdS on ZnO the control of the nucleation/growth kinetics was achieved by means of the control of the reaction temperature and solute concentrations. The obtained samples were characterized by means of XRD, TEM, and SEM, revealing promising core-shell structures with ZnO TP covered by a thin layer (few nanometers) of CdS. Photoluminescence and photo-catalytic activity have been also studied in order to evaluate the properties of the coupled nanostructures.
Subject ZnO
CdS
nanostructures
functionalization
CBD
81.07.Bc Nanocrystalline materials
81.10.Dn Growth from solutions
81.10.Bk Growth from vapor


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