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|23. [Evolutionary Nanomaterials & Nanodevices] K.-B. Lee, C.-S. Choi, S. J. Oh, H.-C. Ri, and Jinwoo Cheon*
Synthesis of Nanocomposite Pd Balls and Wires by Chemical Vapor Infiltration
Le Journal de Physique IV, 11 (PR3), Pr3-481-Pr3-486 (Aug 1, 2001) DOI : https://jp4.journaldephysique.org/articles/jp4/abs/2001/03/jp4200111PR361/jp4200111PR361.html
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.
|22. [Evolutionary Nanomaterials & Nanodevices] Jong-Il Park and Jinwoo Cheon*
Synthesis of “Solid Solution” and “Core-Shell” Type Cobalt−Platinum Magnetic Nanoparticles via Transmetalation Reactions
J. Am. Chem. Soc., 123 (24), 5743-5746 (Jun 1, 2001) DOI : https://pubs.acs.org/doi/abs/10.1021/ja0156340
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
|21. [Evolutionary Nanomaterials & Nanodevices] Young-wook Jun, Sang-Min Lee, Nam-Jung Kang, and Jinwoo Cheon*
Controlled Synthesis of Multi-Armed CdS Nanorod Architectures Using Monosurfactant System
J. Am. Chem. Soc., 123 (21), 5150-5151 (May 1, 2001) DOI : https://pubs.acs.org/doi/full/10.1021/ja0157595
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
|20. [Evolutionary Nanomaterials & Nanodevices] K.-B. Lee, S.-M. Lee, and Jinwoo Cheon*
Size‐Controlled Synthesis of Pd Nanowires Using a Mesoporous Silica Template via Chemical Vapor Infiltration
Adv. Mater, 13 (7), 517-520 (Apr 6, 2001) DOI : https://onlinelibrary.wiley.com/doi/abs/10.1002/1521-4095(200104)13:7%3C517::AID-ADMA517%3E3.0.CO;2-8
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.
|19. [Evolutionary Nanomaterials & Nanodevices] Young-wook Jun, Chang-Shik Choi, and Jinwoo Cheon*
Size and Shape Controlled ZnTe Nanocrystals with Quantum Confinement Effect
Chem. Commun., 1, 101-102 (Dec 19, 2000) DOI : https://www.doi.org/10.1039/B008376N
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.
|18. [Evolutionary Nanomaterials & Nanodevices] Hongkyu Kang, Young-wook Jun, Jong-Il Park, Kyung-Bok Lee, and Jinwoo Cheon*
Synthesis of Porous Palladium Superlattice Nanoballs and Nanowires
Chem. Mater., 12 (12), 3530-3532 (Dec 1, 2000) DOI : https://www.doi.org/abs/10.1021/cm000617f
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.
|17. [Evolutionary Nanomaterials & Nanodevices] Young-wook Jun, Ja-Eung Koo, and Jinwoo Cheon*
One-Step Synthesis of Size Tuned Zinc Selenide Quantum Dots via a Temperature Controlled Molecular Precursor Approach
Chem. Commun., 14, 1243-1244 (Jun 20, 2000) DOI : https://doi.org/10.1039/B002983L
One-step size-controlled synthesis of ZnSe quantum dots is studied and the obtained QDs are luminescent with the emission wavelength varying over a wide range (up to 100 nm) depending on the particle size; the single-molecular precursor is an air-stable bis(phenylselenolato)zinc N,N,N′,N′-tetramethylethylenediamine (TMEDA) complex, which effectively affords different sizes of ZnSe QDs depending on growth temperatures.
|16. [Evolutionary Nanomaterials & Nanodevices] Jinwoo Cheon*, Hong-Kyu Kang, and Jeffrey I. Zink*
Spectroscopic Identification of Gas Phase Photofragments from Coordination Compound Chemical Vapor Deposition Precursors
Coord. Chem. Rev., 200, 1009-1032 (Feb 24, 2000) DOI : https://doi.org/10.1016/S0010-8545(00)00325-8
This review focuses on the gas phase photochemical fragmentation processes of coordination compounds that are precursors for the laser driven synthesis of solid-state materials such as thin films and nanoclusters from the gas phase. Specific emphasis is placed on the identification of photofragments by luminescence spectroscopy during the deposition process. In several cases, results from mass spectroscopy and from photofragmentation under the collision-free conditions of a molecular beam are included to clarify the identifications and mechanisms. Detailed experimental measurements have been made on metal diketonates, metal amides, metal xanthates and metal thiocarbamates. These compounds are useful as molecular precursors for the synthesis of thin films and nanoparticles of metals, binary and ternary materials, and semiconductor films.
|15. [Evolutionary Nanomaterials & Nanodevices] Ana Acosta, Jeffrey I. Zink*, and Jinwoo Cheon
Ligand to Ligand Charge Transfer in (Hydrotris(pyrazolyl)borato)(triphenylarsine)copper(I)
Inorg. Chem., 39 (3), 427-432 (Feb 1, 2000) DOI : https://doi.org/10.1021/ic9908773
Emission and UV−vis absorption spectra of (hydrotris(pyrazolyl)borato)(triphenylarsine)copper(I), (CuTpAsPh3), (hydrotris(pyrazolyl)borato)(triethylamine)copper(I), (CuTpNEt3), and (hydrotris(pyrazolyl)borato)(triphenylphosphine)copper(I), (CuTpPPh3), are reported. The spectra of the arsine complex contain low-energy bands (with a band maximum at 16 500 cm-1 in emission and a weak shoulder centered at about 25 000 cm-1 in absorption) that are not present in the corresponding spectra of the amine or phosphine complexes. The lowest energy electronic transition is assigned to ligand to ligand charge transfer (LLCT) with some contribution from the metal. This assignment is consistent with PM3(tm) molecular orbital calculations that show the HOMO to consist primarily of π orbitals on the Tp ligand (with some metal orbital character) and the LUMO to be primarily antibonding orbitals on the AsPh3 ligand (also with some metal orbital character). The absorption shoulder shows a strong negative
|14. [Evolutionary Nanomaterials & Nanodevices] Jinwoo Cheon and Jeffrey I. Zink*
In-Situ Gas-Phase Luminescence and Time-of-Flight Mass Spectroscopic Detection of Photofragments during Photochemical Synthesis of Copper Particles from Bis(tert-butylacetoacetato)copper
Inorg. Chem., 39 (3), 433-436 (Feb 1, 2000) DOI : https://doi.org/10.1021/ic990962a
During the 308 nm laser-driven photochemical synthesis of Cu particles from bis(tert-butylacetoacetato)copper, gas-phase photogenerated intermediates are identified by luminescence and time-of-flight mass spectroscopies. Pure Cu deposits are obtained as homogeneous, granular 200 nm particles. In the gas phase, luminescent photoproducts are observed and atomic Cu, Cu2, and dissociated ligand are identified spectroscopically. In addition, mass spectroscopy identifies Cu atoms, the dissociated ligand, a monoligated complex, and fragments of the ligands. The implications of the photofragmentation that produces copper atoms and dimers for the laser-assisted production of the Cu deposits are discussed.