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A newly developed robust strategy that utilizes shape- and size-controlled [beta]-Sn nanocrystals as reactive templates, is presented. The analysis helps in the production of various nanocrystals involving elements of notably different reduction potentials, reduction kinetics and reactivity.

A new low-temperature approach to the synthesis of atomically ordered nanocrystals using bimetallic nanoparticle precursors has been demonstrated. It is expected that approach to the synthesis of atomically ordered nanocrystals will be applicable to a wide range of inorganic solids, perhaps even yielding new metastable solids that are not stable in bulk systems.

Issues concerning the synthesis by topochemical means of three-dimensional perovskites from lamellar Dion-Jacobson and Ruddlesden-Popper starting materials are presented. Oxygen loss accompanying the reduction of one of the ions is used to form the perovskites which keep the anisotropic texture of their layered starting materials.

The synthesis of colloidal GeS and GeSe nanostructures obtained by heating Ge[I.sub.4], hexamethyldisilazane, oelylamine, oleic acid and dodecanethiol or trioctylphosphine selenide is described. Optimal measurements have shown indirect ban gaps for GeS and GeSe and electrical measurements have shown that drop-cast films of GeSe have displayed p-type conductivity.

The chemical synthesis and characterization of [alpha]-Mn nanoparticles in the presence of n-butyllithium as a reducing agent are reported. Oleate ligand bound amorphous manganese oxide layer rendered the nanoparticles air-stable while the oxide-coated [alpha]-Mn nanoparticles are found to be paramagnetic.

Solution chemistry methods are used for preparing bimetallic CuPt alloy nanoparticle catalysts with controllable sized and shapes. The mixed-metal nanoparticles have displayed excellent catalytic properties for CO oxidation, with light-off temperatures that are nearly 200 K below those of conventional supported Pt catalysts.

ZnO nanoparticles, which adopt the wurtzite (WZ) structure, have served as structural templates for the controllable formation of WZ-type ZnS and ZnSe. The results have highlighted the importance of forming WZ-type ZnO as a reaction intermediate in order to preferentially stabilize the WZ forms of ZnS and ZnSe.

The process of transforming single-component metal nano wires into multisegment nanowires with multimetal components is discussed. These solution chemistry conversion reactions provide a cpnvenient tool kit for engineering complex solid-state compoenets into template-grown metal nanowires.

A recently developed kinetically controlled borohydride reduction process, which helps in the chemical synthesis of shape-controlled indium (In) nanoparticles at room temperature, is presented. These nanoparticles are shown to exhibit high conductivity and surface plasmon resonance (SPR) properties, which make them suitable for several optical and magnetic applications.

A new strategy is described for synthesizing nanostructures of transition metal phosphides, which has used the conversion of preformed metal nanoparticles into metal phosphides by solution-mediated reaction with trioctyphosphine (TOP). The results have shown that in addition to its utility for accessing transition metal phosphides using a highly robust method, various aspects of nanostructure can be influenced by controlling critical aspects of the metal nanoparticle precursors.

An unusual multistep reaction pathway that leads to the formation of AuCuS[n.sub.2], a new ternary intermetallic compound that was discovered as nanocrystals using a low-temperature solution route is described. The multistep reaction pathway provides compelling evidence that a nanocomposite forms in solution and transforms into alloy and intermetallic nanocrystals via solution-mediated reactions.

Nanocrystals of intermetallic compounds undergo facile solution-mediated reactions to form derivative phases, where these intermetallics can be used as reagents for the low-temperature solution synthesis of other intermetallic phases. This work has added to a growing toolbox of low-temperature reactions for accessing nanocrystalline alloys and intermetallics and also has helped in the formation of new and complex solids.

The example of hollow magnetic CoPt nanopheres synthesized through a novel and potentially general one-pot reaction that exploits an in situ sacrificial template is reported. One of the important implications of the successful synthesis of hollow nanospheres of a CoPt allow phase is that the alloy system have received much less synthetic development than single-metal systems.

The study demonstrated that metal nanoparticles could be used as a robust solution-based toolkit for synthesizing intermetallic compounds and alloys within minutes at low temperatures. The strategy exploits the enhanced reactivity and nanoscale diffusion distances afforded by binary nanoparticle composites to eliminate the need for high-temperature heating and atomic-scale homogenization, which are necessary using traditional methods for solid-state synthesis.

Low-temperature solution routes originally developed for the synthesis of nanocrystals and nanocrystalline powders can be exploited to access new ordered intermetallics with ternary compositions. The Au-Cu-Sn system was studied since ternary phase diagrams are difficult to map.

Controlling the composition and phase formation of bulk and nanoscale solids underpins efforts to control physical properties. Here, we introduce a powerful new chemical pathway that facilitates composition-tunable synthesis, post-synthesis purification, and precise phase targeting in metal chalcogenide systems. `When metal sele-nides and sulfides react with trioctylphosphine (TOP) at temperatures that range from 65 to 270 °C, selenium and sulfur are selectively extracted to produce the most metal-rich chalcogenide that is stable in a particular binary system. This general approach is demonstrated for SnSe2, FeS2, NiSe2, and CoSe2, which convert to SnSe, FeS, Ni3Se2, and Co9Se8, respectively. In-depth studies of the Fe-Se system highlight the precise phase targeting and purification that is achievable, with PbO-type FeSe (the most metal-rich stable Fe-Se phase) forming exclusively when other Fe-Se phases, including mixtures, react with TOP. This chemistry also represents a new template-based nanoparticle "conversion chemistry" reaction, transforming hollow NiSe2 nano-spheres into hollow NiSe nanospheres with morphological retention. [ABSTRACT FROM AUTHOR]

The ability to control the shape of metal nanocrystals is critical to applications such as catalysis, magnetism, and plasmonics. Despite significant advances in controlling the shapes of single-metal nanocrystals, rigorous shape control of multimetal nanocrystals remains challenging, and has been limited largely to alloy systems of similar metals. Here we describe a robust strategy that produces shape-controlled intermetallic nanocrystals involving elements of notably different reduction potentials, reduction kinetics, and reactivity. The approach utilizes shape- and size-controlled β-Sn nanocrystals as reactive templates that can be converted into binary M-Sn (M = Fe, Co, Ni, Pd) intermetallic compounds by reaction with appropriate metal salt solutions under reducing conditions. The result, demonstrated in detail for the FeSn2 system, is a variety of nanostructures with morphologies that include spheres, cubes, hollow squares, U-shaped structures, nanorods, and nanorod dimers. Our experiments demonstrate a size- and shape-dependent reactivity toward the formation of hollow FeSn2 nanostructures and provide empirical guidelines for the formation of other intermetallic nanocrystals. In addition to those of FeSn2, nanocrystals of intermetallic PdSn, CoSn3, and NiSn3 can be formed using this same chemical conversion strategy. [ABSTRACT FROM AUTHOR]

Understanding how solids form is a challenging task, and few strategies allow for the elucidation of reaction pathways that are useful for designing new solids. Here, we describe an unusual multistep reaction pathway that leads to the formation of AuCuSn2, a new ternary intermetallic compound that was discovered as nanocrystals using a low-temperature solution route. The formation of AuCuSn2 using a modified polyol process occurs through a multistep pathway that was elucidated by taking aliquots throughout the course of the reaction and studying the products using a variety of techniques. The reaction proceeds through four distinct steps: (a) formation of Au nanoparticles at or near room temperature, mediated by a galvanic reaction between Au3+ and Sn2+ (forming Au0 and Sn4+, precipitated as SnO2 that forms a shell around the nanoparticles), (b) formation of NiAs-type AuSn nanoparticles, along with Cu and Sn, upon addition of NaBH4, (c) aggregation and thermal interdiffusion to form AuCuxSny alloy nanoparticles, and (d) nucleation of intermetallic AuCuSn2, which has an ordered NiAs-derived structure. The proposed mechanism was tested by starting the reaction with the AuSn intermediate. AuSn nanoparticles were synthesized separately and reacted with Cu and Sn nanoparticles, and ordered AuCuSn2 formed as expected. Elucidation of this reaction pathway has important implications for guiding the design of new intermetallic solids, as well as for controlling the synthesis of complex multimetal nanocrystals. [ABSTRACT FROM AUTHOR]

A new multistep approach was developed to synthesize atomically ordered intermetallic nanocrystals, using AuCu and AuCu3 as model systems. Bimetallic nanoparticle aggregates are used as precursors to atomically ordered nanocrystals, both to precisely define the stoichiometry of the final product and to ensure that atomic-scale diffusion distances lower the reaction temperatures to prevent sintering. In a typical synthesis, PVP-stabilized Au-Cu nanoparticle aggregates synthesized by borohydride reduction are collected by centrifugation and annealed in powder form. At temperatures below 175 °C, diffusion of Cu into Au occurs, and the atomically disordered solid solution CuxAu1-x exists. For AuCu3, nucleation occurs by 200 °C, and atomically ordered AuCu exists between 200 and 400 °C. For AuCu3, an AuCu intermediate nucleates at 200 °C, and further diffusion of Cu into the AuCu intermediate at 300 °C nucleates AuCu3. Atomically ordered AuCu and AuCu3 nanocrystals can be redispersed as discrete colloids in solution after annealing between 200 and 300 °C. [ABSTRACT FROM AUTHOR]