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|22. [Evolutionary Nanomaterials & Nanodevices] K‐B Lee, S‐M Lee, Jinwoo Cheon
Size‐Controlled Synthesis of Pd Nanowires Using a Mesoporous Silica Template via Chemical Vapor Infiltration
Advanced Materials, 13 (7), 517-520 (Apr 6, 2001)
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.
|21. [Evolutionary Nanomaterials & Nanodevices] Young-wook Jun, Jong-Il Park, Jinwoo Cheon
Convenient molecular approach of size and shape controlled ZnSe and ZnTe nanocrystals
MRS Online Proceedings Library Archive, 635 (Mar 17, 2001)
Our study describes a convenient one-step synthesis of ZnSe and ZnTe nanocrystals (NC) whose sizes and shapes are precisely tuned by varing the growth temperature or stabilizing surfactants. We utilized molecular precursors, bis(phenylselenolate or phenyltellurolato)zinc -N,N,N',N'-tetramethylethylenediamine (TMEDA), which effectively produce 0-dimensional sphere or 1-dimensional nanorods of ZnSe or ZnTe, respectively. Nanocrystals are highly monodispersed and luminescent; the emission wavelength varies over a wide range depending on the particle size. This study constitutes a nice demonstration of direct size and shape controlled synthesis of semiconductor nanocrystals and this method can be extended to the synthesis of nanocrystals of other materials.
|20. [Evolutionary Nanomaterials & Nanodevices] Jinwoo Cheon, Kyung-Bok Lee, Hongkyu Kang, SJ Oh, H-C Ri
Matrix-assisted synthesis of palladium nanocage and nanowires
MRS Online Proceedings Library Archive, 635 (Jan 1, 2001)
Our study describes the synthesis of novel nanoscale Pd cage and wires whose sizes and shapes are templated by mesoporous matrices. The templates used are cubic phase MCM-48 and hexagonal phase CnMCM-41 (n = 16, and 22), SBA-15, which have pore diameters of ∼3, ∼3.8, ∼4.7, and ∼9 nm, respectively. 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 cages (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. All the materials are examined by TEM, XRD, BET, and EDAX analysis. Furthermore, the thermal behavior of Pd nanowire is briefly described.
|19. [Evolutionary Nanomaterials & Nanodevices] Young-wook Jun, Chang-Shik Choi and Jinwoo Cheon*
Size and shape controlled ZnTe nanocrystals with quantum confinement effect
Royal Society of Chemistry, 1, 101-102 (Dec 19, 2000)
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, Jinwoo Cheon
Synthesis of porous palladium superlattice nanoballs and nanowires
American Chemical Society, 12 (12), 3530-3532 (Dec 18, 2000)
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, Jinwoo Cheon
One-step synthesis of size tuned zinc selenide quantum dots via a temperature controlled molecular precursor approach
Chemical Communications, 14, 1243-1244 (May 30, 2000)
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, Jeffrey I Zink
Spectroscopic identification of gas phase photofragments from coordination compound chemical vapor deposition precursors
Coordination Chemistry Reviews, 200, 1009-1032 (May 1, 2000)
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] Jinwoo Cheon, Peter Muraoka, Jeffrey I Zink
Laser-induced deposition of palladium and gas-phase photofragmentation pathways from (2-methylallyl)(1, 1, 1, 5, 5, 5-hexafluoro-2, 4-pentanedionato) palladium
Chemistry of materials, 12 (2), 511-516 (Feb 21, 2000)
Metallic palladium films are prepared at 10-2 Torr by 308 nm irradiation of gaseous (2-methylallyl)(1,1,1,5,5,5-hexafluoro-2,4-pentanedionato) palladium. Gas-phase luminescence spectra recorded during the photochemical deposition process are used to identify photofragments. X-ray photoelectron analysis of the films shows that they consist primarily of palladium metal; the films produced with H2 carrier gas have no detectable fluorine and barely discernible carbon contaminants. The Pd films are polycrystalline fcc (face-centered cubic) palladium with preferential growth along the 111 direction. Scanning electron microscopy shows that the films formed with H2 carrier gas are smooth and consist of granules less than 35 nm in diameter. Further characterization of the gas-phase photofragmentation process is carried out by time-of-flight mass spectroscopy. The dominant peak present in the mass spectrum under 308 nm irradiation arises from palladium ions. No fragments containing palladium and
|14. [Evolutionary Nanomaterials & Nanodevices] Ana Acosta, Jeffrey I Zink, Jinwoo Cheon
Ligand to ligand charge transfer in (hydrotris (pyrazolyl) borato)(triphenylarsine) copper (I)
Inorganic chemistry, 39 (3), 427-432 (Feb 7, 2000)
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
|13. [Evolutionary Nanomaterials & Nanodevices] Jinwoo Cheon, 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
Inorganic chemistry, 39 (3), 433-436 (Jan 21, 2000)
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.