Spherical metallic nanoparticles growth

To maximize fluorophore excitation and increase the fluorescence quantum yield, the spectral properties of the metal nanoparticles need to be optimized. While spherical colloidal nanoparticles of noble metals have been well known for many years, it is only recently that there has been an explosion of reports on the preparation and properties of anisotropically-shaped materials. As will be discussed in the following sections, a wide range of morphologies can be produced, including triangular nanoplates (nanoprisms), cubes, octahedra, nanowires, nanorods and bi-pyramids. The last few years have also seen major developments in our understanding of the growth processes involved, so that now it is possible to prepare many types of shaped p>articles in a controlled fashion. 

A similar approach was followed in the manufacture of Co-Ni nanoparticles which were chemically reduced in a surfactant solution. The spherical particles formed spontaneously and had an average radius of 1.68 0.15nm. Further growth was stopped by the attachment of surfactant molecules to the formed particles. The EXAFS data showed that the coordination number of the metallic atoms in the first shell was lower than in bulk metals. This confirms that a disordered but mainly metallic entity is formed with the atoms on the outside having a higher oxidation degree than those on the inside. It should be remarked here that the error bar on the radius derived from the SAXS data is not necessarily a real error but more likely represents the spread in particle diameter. 

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