Synthesis and Characterization of Monodisperse Ni-Co Bimetallic Nanocrystals

摘要

Monodisperse Ni-Co bimetallic nanocrystals have been intensively investigated during the past several decades because of their unique physical and chemical properties that are promising for a broad range of applications in emerging technologies. The precise control of shape, size, and structure of nanocrystals is critical for the desired functionality, while transmission electron microscopy (TEM) is one of the most powerful and versatile techniques to characterize the nanocrystal's structure, morphology, and physical and chemical properties on the atomic to nanometer scales. The research of this thesis focuses on the synthesis of bimetallic Ni-Co nanocrystals and the understanding of the underlying crystal growth mechanism through advanced structural and chemical characterizations using TEM techniques. We have studied the effect of synthetic temperature, reaction time, concentration of precursors and surfactant on the nanocrystal's morphology and structure. Throughout a series experimental attempts, an optimal set of synthesis parameters was found, which produced the controlled synthesis of Ni-Co nanocrystals with average size of 10.59±1.42 nm from the thermal decomposition reaction at 230°C for 4 h. With the help of TEM, dynamic morphology evolution of Ni-Co nanocrystals as a function of reaction time was discovered and the associated monodisperse nanocrystal growth through digestive ripening mechanism was also elucidated. We have also found that the addition of trioctyphosphine (TOP) surfactant not only regulates the shape and size, but also causes the formation of nickel/cobalt phosphide during nanocrystal growth, which needs further investigation to clarify. The findings obtained from this research provides fundamental understanding of crystal growth mechanism of bimetallic Ni-Co nanocrystals and may also offer useful implications for controlled synthesis of other bimetallic systems.