Cheon Lab

With a baton the general directs soldiers and the conductor musicians, and in the nanoworld the rodlike shape also means control, as this form enhances magnetic and coercive properties of crystalline aggregates. Also reported here is a tunable synthetic method, in which the overall shape of the crystal is determined by a balance of kinetically and thermodynamically controlled growth mechanisms. The graphic shows one example of the degree of ordering available in the crystalline through this method.

We demonstrate that the controlled distribution of nanoparticles can be achieved by employing the ...

Synthesis of ‘solid solution’ and ‘core-shell’ types of well defined Co-Pt based nanoalloys smaller than 10nm have been achieved by redox transmetalation reactions. This redox transmetalation are selectively observed only if the redox potential between two metals is favorable. The composition of the magnetic alloys can also be tuned by adjusting the ratio of reactants. Annealed core-shell nanoparticles transformed into mixed nanoalloys with face centered tetragonal (fct) structures, which show large coercivity and ferromagnetism at room temperature. These nanoparticles can potentially be used as an independent single magnetic bit of tera-bit information storage. Also, this kind of redox transmetalation reaction can be utilized as a general process to synthesize various types of nanoalloys with controlled composition in a selective fashion.

Shape- and dopant-controlled magnetic semiconductor nanocrystals have been achieved by the thermolysis of nonpyrophoric and less reactive single molecular precursors under a monosurfactant system. Reaction parameters governing both the intrinsic crystalline phase and the growth regime (kinetic vs thermodynamic) are found to be important for the synthesis of various shapes of MnS nanocrystals that include cubes, spheres, 1-dimensional (1-D) monowires, and branched wires (bipods, tripods, and tetrapods). Obtained nanowires exhibit enhanced optical and magnetic properties compared to those of 0-D nanospheres. Proper choice of molecular precursors and kinetically driven low-temperature growth afford dopant controlled 1-D Cd1-xMnxS nanorods at high levels (up to ∼12%) of Mn, which is supported by repeated surface exchange experiments and X-ray diffraction (XRD) and electron paramagnetic resonance (EPR) analyses.

Our study presents the preparation of well-defined Pd nanoballs and nanowires using the different pore size of cubic and hexagonal shaped MCM type mesoporous silicate materials as matrix templates. The synthesis involves loading the organometallic precursor into template matrix via chemical vapor infiltration (CVI), followed by mild thermal decomposition to generate Pd metals self-organized inside the template. For Pd@MCM-48, the Pd metal forms spherical domains (~38 nm) consisting of three dimensionally interconnected into Pd arrays; for Pd@SBA-15 and Pd@MCM-41, the Pd metal forms of one-dimensional wires. Etching out the matrix produces porous Pd nanoballs (pore sizes of ~1.5 - 2.0 nm) with retaining original domain sizes of ~38 nm; similarly Pd@SBA-15 and Pd@MCM-41 afford freestanding Pd nanowires. In addition, phase transition behavior and melting point depression of the Pd nanowires is studied.

In this article, we report the synthesis of “solid solution” and “core-shell” types of well-defined Co−Pt nanoalloys smaller than 10 nm. The formation of these alloys is driven by redox transmetalation reactions between the reagents without the need for any additional reductants. Also the reaction proceeds selectively as long as the redox potential between the two metals is favorable. The reaction between Co2(CO)8 and Pt(hfac)2 (hfac = hexafluoroacetylacetonate) results in the formation of “solid solution” type alloys such as CoPt3 nanoparticles. On the other hand, the reaction of Co nanoparticles with Pt(hfac)2 in solution results in “CocorePtshell” type nanoalloys. Nanoparticles synthesized by both reactions are moderately monodispersed (σ < 10%) without any further size selection processes. The composition of the alloys can also be tuned by adjusting the ratio of reactants. The magnetic and structural properties of the obtained nanoparticles and reaction byproducts are characterized

Recently, nanomaterials have drawn interests owing to their special characteristics which differ from bulk crystals.1-7 The synthesis of colloidal inorganic nanocrystals especially with respect to the control of their shape, however, is under developed and still complicated. Since novel properties of nanomaterials depend on their size and shape, a new direction for synthetic methods and an understanding of the mechanisms by which the size and shape of the nanocrystals can be easily varied are key issues in nanochemistry

Free‐standing Pd nanowires of controlled size are synthesized by these authors via chemical vapor infiltration of an organometallic precursor into mesoporous silicate. The thus generated Pd nanowires can be isolated by addition of HF to remove the silicate matrix. Wires ranging from 3.7–8.8 nm in diameter and up to several hundred nanometers in length can be obtained (see Figure), depending on the silica template used.

A simple one-pot synthesis of size and shape controlled ZnTe nanocrystals using a monomeric molecular precursor, [Zn(TePh)2][TMEDA], has been studied by varying the growth temperature or the templating surfactants.

Ordered arrays of palladium nanostructures have been obtained inside MCM-48 and SBA-15, using chemical vapor infiltration. Removal of the silica matrix affords porous three-dimensional Pd nanoballs and one-dimensional Pd nanowires, depending on the architecture of the silicate host.