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Abstract
Core/shell nanoparticles are an interesting branch of materials as a thin surface layer on fine particles can change their functionalities and properties, such as chemical reactivity, thermal stability, catalytic activity, optical, magnetic, and electronic properties. Thus, reaching to advanced properties and multifunctionality became a primary research goals in order to achieve novel applications, which led to discoveries of new materials and potential methods for combining different properties in one structure.
Inert-gas condensation (IGC) is a bottom-up method to produce nanoparticles by condensation from a gas phase. The advantages of IGC is flexibility of this method in terms of the range of particle size. Moreover, because of its ability to work in high or ultrahigh vacuum environments, the chemical purity of the nanoparticles is guaranteed.
In this dissertation, IGC was used to produce core/shell CoZnO nanoparticles. First, two different methods were used for producing oxidized nanoparticles as: ex situ oxidation and in situ oxidation. Each of these methods resulted to different crystal structures of the oxidized shell, while the crystal structure of the core was consistent. Moreover, partial epitaxial growth of shell on top of core in in situ-oxidized particles was possible.
Next, individual nanoparticles were tested electrically to investigate resistive switching behavior. Both ex and in situ-oxidized nanoparticles showed characteristic resistive switching behavior with relatively high memory window which makes them promising candidate for resistive switching memory application.
Magnetic hysteresis of the nanoparticles versus applying magnetic field also was measured. The ferromagnetic behavior of magnetic hysteresis in both ex and in situ-oxidized nanoparticles showed that ZnO-shell protected the Co at the core from oxidation. This is necessary for measuring the magnetoresistance effect of nanoparticles.
Finally, in situ nanoparticles were deposited between some metal electrodes to build memory devices. The devices also showed the resistive switching behavior with relatively low “set” and “reset” voltages.
