| Summary: | 碩士 === 國立臺灣大學 === 化學研究所 === 89 === The controlled evolution of size and shape of inorganic nanocrystals is an important goal in the science of nanomaterials. We synthesize Au spherical nanocrystals protected by didodecyldimethyl ammonium bromide (DDAB) in toluene by phase transfer method. The toluene Au colloidal solution was treated with NaSCN microcrystals at various temperature (-19~60℃) for five days. We observe shape transformation of the Au nanocrytals into uniform short nanorods (7~9nm in minor axis and 15~20nm in major axis, aspect ratio<2) and nanosquare-plates (12~14nm in diameter). The Au nanosquares can form superlattice. Selected area electron diffraction pattern of the superlattice shows that the Au nanosquares are preferentially oriented along [001] orientation.
Here, we also change the reaction condition, such as the amount of NaSCN, surfactant concentration, crystal species, crystal surface area, temperature, solvent, reaction time and use the particle metallic projection and HR-TEM technologies to definitely propose the shape transformation mechanism. We propose the shape evolution occurs through an unusual oriented attachment process of Au spherical nanocrystals supported hetero-epitaxially on the NaSCN surface. And we also discover that the (001) surface of NaSCN crystal has an epitaxial lattice match with Au surfaces.
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