Shape-Controlled Synthesis of Metal Nanocrystals

Xia, Y., Xiong, Y., Lim, B., and Skrabalak, S.E. (2009) Shape-controlled synthesis of metal nanocrystals simple chemistry meets complex physics Angewandte Chemie International Edition, 48 (1), 60-103. 

Colloidal synthesis of metal chalcogenides has been developed to be used as nanocrystal inks to produce high efficiency solar cells with the lower fabrication costs. Recent research on these materials has focused on the use of abundant and low toxicity elements such copper, iron, tin, lead and sulphur. Several methods have been developed for the synthesis of these materials and considerable progress has been made in controlling the size, shape and surface properties of the nanocrystals. This chapter will provide the most recent developments for the synthesis and use of colloidal nanocrystal inks for solar energy. 

Thermal decomposition In order to control shape and size more precisely, the method of thermal decomposition is developed. This is a method similar to the synthesis of semiconductors with high-quality nanocrystals. The smaller magnetic nanocrystals can be formed from organometallic compounds in organic solvents. By adding precursor in zerovalent, thermal decomposition will have metal formed in the end. When the decomposition happens, cationic metal will lead the electrons to the oxides and the reaction solution will have metal acid salts in nonaqueous solution. With the metal fatty acid compound in the solution, the metal will reach saturation and the metal magnetic... 

While the microemulsion method has been widely applied to the production and stabilization of spherical metal particles with various sizes and compositions, shape control of noble metallic particles using this procedure has only been demonstrated in a handful of studies to date. Pileni and co-workers demonstrated that it is possible to control nanocrystal shape to some extent within microemulsions.Although the shape of the templates plays a role during the growth of the nanocrystals, these authors showed that the particle shape can be controlled even if the microscopic structure of the self-assembled surfactant system used as a template remains unchanged and that addition of salt to the templates can induce drastic changes in the particle shape. Recently, the same group also reported the synthesis of silver nanodisks in reverse micellar solution by reduction of Ag(AOT) with hydrazine, with various sizes that depended on the relative amount of hydrazine, but with constant aspect ratio. 

In the one-step synthesis of FePt nanoparticles, platinum acetylacetonate (Pt(acac)2) and iron pentacarbonyl (Fe(CO)5) and Fe(CO)5 was mixed at excess of stabilizers at 100 °C, then the mixture was heated to more than 200 °C, and kept it at that temperature for Ih, before it was heated to reflux [215, 223]. It was found that with benzyl ether as solvent and oleic acid and oleylamine as stabilizers, one-pot reaction of Fe(CO)5 and Pt(acac)2 could give nanosized FePt particles (3 - 4 nm). Size, composition, and shape of the particles were controlled by varying the synthetic parameters such as molar ratio of stabilizers to metal precursor, addition sequence of the stabilizers and metal precursors, heating rate, heating temperature, and heating duration. Monodisperse FePt nanocrystals were prepared by hydrolysis of pentacarbonyl iron and reduction of metal complexes in the presence of oleic acid and oleylamine [215]. 

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