(70b) Monodisperse Ag-Au Alloy Nanoparticles with Independently Tunable Composition, Size, Internal Structure and Surface Chemistry, and Their 3-D Superlattices

Ag and Au nanoparticles, with their highly customizable optical, electronic and catalytic properties, are rich resources for nanotechnology applications. By combining the two metals into a common entity to form an alloy nanoparticle, these properties can be further modified through composition tuning, leading to new possibilities and potential enhancement of application performance. As nanoparticle properties are strongly dependent on the particle attributes, it is imperative to develop synthetic procedures where alloy nanoparticles with controllable composition, size, internal structure and surface chemistry may be produced reliably and in large quantities.

Herein we report the synthesis of highly monodisperse Ag-Au alloy nanoparticles by a solution chemistry method. The alloy nanoparticles were characterized by high resolution transmission electron microscopy (HRTEM), selected-area energy dispersive x-ray spectroscopy (SAEDX), UV-visible absorbance spectroscopy and electron diffraction. Alloy nanoparticles with two different types of internal structures were produced: one was single-crystalline truncated octahedral nanoparticles; and another was icosahedral multiply twinned particles (MTPs). For each structure, the composition, size and surface properties of the nanoparticles could be individually varied while keeping the other attributes constant. The successful preparation of monodisperse alloy nanoparticles with independently tunable particle attributes is valuable to the study of the physicochemical properties of the particles as a function of the composition, size, internal structure and surface chemistry.

The as-synthesized alloy nanoparticles could assemble to form 2-D and 3-D superlattices on substrates. The distance between two particles could be adjusted by the length of the protective agent. The structures of the superlattices formed by single crystalline and multiple twinned alloy particles were different. The single-crystalline Ag-Au alloy nanoparticles in the superlattices display both translational and orientational ordering. The multiply twinned icosahedral alloy nanoparticles only display translational ordering. The 2-D and 3-D superlattices may be used to study the effects of the close coupling of proximal alloy nanoparticles on their application properties.