Functionalization effects in vapour-phase grown ZnO nanostructures coupled with CdS nanoparticles

It is well known that the enormous potentiality of this ZnO rises not simply from the possibility to combine all its functional properties with the large variety of available ZnO nanostructures, but mainly from the nearly infinite number of possible surface functionalizations by different materials thet can add, modify or improve its intrinsic properties. Authors previously reported about the optimized vapor phase synthesis of different ZnO nanostructures [1-3]. Among the possible functionalizations, a detailed study on cadmium sulphide (CdS) deposition over ZnO nanorods and tetrapods is here reported. At first, a focused optimization of CdS synthesis process have been faced in order to avoid the typical damaging of ZnO surfaces in alkaline solutions, that are generally used for the synthesis of calcogenide nanostructures. This damaging can be responsible, indeed, for bad charge carriers transfer in among the materials coupled in heterojunction. The best results, from has been achieved with a DMFA solution based chemical process that allowed authors to control the heteronucleation of CdS nanoparticles directly on the ZnO surface. Then fundamental and functional characterizations, such as SEM, TEM, XRD, PL, photo-induced currents, photocatalytic activity and gas sensing properties, have been performed in order to study the effects of materials coupling on ZnO chemical and physical properties. In particular, some evidence of excitonic charge transfer and a selective inversion of the response towards specific gases in the obtained CdS-functionalized ZnO nanostructures have been observed and discussed.