Cheon Lab

Main Links

Logo and Main Menu

Full Menu

Research

Search

Total: 152 data, Page 15 of 16

12. [Evolutionary Nanomaterials & Nanodevices] Jinwoo Cheon, Matthew Guile, Peter Muraoka, Jeffrey I Zink
Gas phase photoproduction of diatomic metal nitrides during metal nitride laser chemical vapor deposition
Inorganic chemistry, 38 (9), 2238-2239
 (May 3, 1999)

Photolysis of M(NEt2)4 in the gas phase produces diatomic MN molecules (M = Ti, Zr, Hf). TiN and ZrN molecules were identified in the gas phase under CVD conditions by emission spectroscopy and time-of-flight mass spectroscopy. Nanostructured deposits of TiN were formed on quartz substrates by irradiating Ti(NEt2)4 gas at 355 nm. These studies demonstrate the gas phase formation of diatomic molecules having the same stoichiometry as that of the desired solid-phase deposit.

11. [Evolutionary Nanomaterials & Nanodevices] A Stavrides, J Ren, M Ho, Jinwoo Cheon, J Zink, HP Gillis, RS Williams
Growth and characterization of diamond-like carbon films by pulsed laser deposition and hydrogen beam treatment
Thin Solid Films, 1-2, 27-31
 (Nov 19, 1998)

Amorphous diamond-like carbon films have been grown by pulsed laser deposition using a graphite target both with and without an atomic hydrogen beam incident on the growing film. Films grown with the hydrogen beam showed resistivity nearly two orders of magnitude higher than the films grown without hydrogen. Raman scattering confirmed a higher degree of sp3 bonding in films exposed to hydrogen atoms during growth. Films grown without hydrogen but exposed to the hydrogen beam after growth showed a significant increase in resistivity after exposure.

10. [Evolutionary Nanomaterials & Nanodevices] Jinwoo Cheon, John E Gozum, Gregory S Girolami
Chemical Vapor Deposition of MoS2 and TiS2 Films From the Metal−Organic Precursors Mo(S-t-Bu)4 and Ti(S-t-Bu)4
Chem. Mater., 9 (8), 1847-1853
 (Aug 14, 1997)

The deposition of MoS2 and TiS2 thin films from the metal-organic precursors Mo(S-t-Bu)4 and Ti(S-t-Bu)4 has been investigated. Stoichiometric films with low levels of oxygen and carbon contaminants can be grown at temperatures between 110 and 350 °C and low pressure. The films are amorphous when grown at these low temperatures and have granular morphologies in which the grains are 30−90 nm in diameter, the larger grain sizes being observed at higher deposition temperatures. For the MoS2 deposits, the electrical conductivity was ∼1 Ω-1cm-1. For both precursors, the organic byproducts generated during deposition consist principally of isobutylene and tert-butylthiol; smaller amounts of hydrogen sulfide, isobutane, di-tert-butyl sulfide, and di-tert-butyl disulfide are also generated. A β-hydrogen abstraction/proton-transfer mechanism accounts for the distributions of the organic byproducts seen during the deposition of MoS2 and TiS2 films. Our results differ in some respects from those

9. [Evolutionary Nanomaterials & Nanodevices] Jinwoo Cheon, Deborah M. Rogers, and Gregory S. Girolami
Mechanistic Studies of the Thermolysis of Tetraneopentyltitanium(IV). 1. Solution Evidence That Titanium Alkylidenes Activate Saturated Hydrocarbons
J. Am. Chem. Soc., 119 (29), 6804-6813
 (Jul 23, 1997)

Studies of the thermolysis of Ti(CH2CMe3)4 in solution have been carried out in parallel with studies of the chemical mechanism responsible for its conversion to titanium carbide under CVD conditions. In hydrocarbon solutions, the neopentyl complex thermolyzes to eliminate 2.1 equiv of neopentane as the principal organic product. A deuterium kinetic isotope effect (kα(H)/kα(D) = 5.2 ± 0.4) upon deuterating the alkyl groups at the α positions provides clear evidence that the initial step in the thermolysis is an α-hydrogen abstraction reaction to form neopentane. The activation parameters for this α-hydrogen abstraction process are ΔH⧧ = 21.5 ± 1.4 kcal/mol and ΔS⧧ = −16.6 ± 3.8 cal/(mol K). The titanium-containing product of this reaction is a titanium alkylidene, which in solution activates C−H bonds of both saturated and unsaturated hydrocarbon solvents such as benzene and cyclohexane. No activation of the C−F bonds of hexafluorobenzene is seen, however. Under special circumstances,

8. [Evolutionary Nanomaterials & Nanodevices] Jinwoo Cheon, Lawrence H Dubois, Gregory S Girolami
Mechanistic studies of the thermolysis of tetraneopentyltitanium (IV). 2. Solid state and ultra-high-vacuum studies of the chemical vapor deposition of TiC films
J. Am. Chem. Soc., 119 (29), 6814-6820
 (Jul 23, 1997)

The chemical pathway responsible for the conversion of the organotitanium compound tetraneopentyltitanium to titanium carbide has been studied under chemical vapor conditions and on single crystals in ultra-high vacuum. For every equivalent of TiNp4 consumed in the deposition process, 3.28 equiv of neopentane and 0.16 equiv of isobutane are produced; other organic species are also formed but in relatively small amounts. About 93% of the carbon and hydrogen originally present in the precursor can be accounted for in these products. Thermolysis of the specifically deuterated analogue Ti(CD2CMe3)4 yields a 2.25:1 ratio of neopentane-d3 and neopentane-d2; this result combined with a kinetic isotope effect of 4.9 at 385 K shows unequivocally that the first step in the deposition pathway under CVD conditions is α-hydrogen abstraction. The α-hydrogen abstraction step produces 1 equiv of neopentane and a titanium alkylidene, which undergoes further α- (and eventually γ-) hydrogen activation pr

7. [Evolutionary Nanomaterials & Nanodevices] Jinwoo Cheon, David S. Talaga, and Jeffrey I. Zink
Laser and Thermal Vapor Deposition of Metal Sulfide (NiS, PdS) Films and in Situ Gas-Phase Luminescence of Photofragments from M(S2COCHMe2)2
Chem. Mater., 9(5), 1208–1212
 (May 15, 1997)

NiS and PdS thin films are prepared at 10-2 Torr from the single-source precursors M(S2COCHMe2)2, M = Ni and Pd. Two different vapor deposition processes, photochemical and thermal, are employed. Gas-phase emission spectroscopy is used during the photochemical deposition to identify the two elemental components of the final materials, the metal atom and sulfur, in the gas phase. NiS and PdS thin films are grown by the thermal process at 300 and 350 °C, respectively, on Si and quartz substrates. The NiS films are highly oriented rhombohedral (γ) phase, and the PdS films are tetragonal-phase polycrystalline. The metal sulfide films are grown photolytically by 308 nm laser irradiation of the gas-phase precursors at lower temperatures (near the sublimation temperature). The NiS films show no X-ray diffraction patterns, but the PdS films are polycrystalline tetragonal phase. The films are analyzed by various surface analytical tools including scanning electron microscopy, X-ray photoelectro

6. [Evolutionary Nanomaterials & Nanodevices] Jinwoo Cheon and Jeffrey I. Zink*
Gas Phase Photochemical Synthesis of II/VI Metal Sulfide Films and in Situ Luminescence Spectroscopic Identification of Photofragments
J. Am. Chem. Soc., 119(16), 3838–3839
 (Apr 23, 1997)

The wide band gap II/VI semiconductors are of current interest for optoelectronic applications such as blue lasers, light-emitting diodes, and optical devices based on nonlinear properties.1,2In particular, ternary phase materials (e.g., ZnxCd1-xS) have attracted technological interest because the band gap can be tuned and the lattice parameters can be varied. Chemical vapor deposition (CVD) of II/VI materials from pyrolysis of metal complexes with sulfur-chelating ligands (dithiocarbamate, dithiophosphate) has been reported,3 but photoassisted CVD is rare.

5. [Evolutionary Nanomaterials & Nanodevices] Jinwoo Cheon, David S. Talaga, and Jeffrey I. Zink*
Photochemical deposition of ZnS from the gas phase and simultaneous luminescence detection of photofragments from a single-source precursor, Zn (S2COCHMe2) 2
J. Am. Chem. Soc., 119(1), 163-168
 (Jan 8, 1997)

ZnS thin films are made by laser driven chemical vapor deposition (CVD) from a single-source precursor, Zn(S2COCHMe2)2 under vacuum conditions. Photofragments in the gas phase are identified simultaneously by luminescence spectroscopy. The laser selectively activates the initial decomposition of the precursor and drives its conversion to the desired materials under mild conditions. These photolytically produced films are compared to films made by thermal deposition from the same precursor. The deposits from both techniques, characterized by X-ray diffraction, Rutherford backscattering, and X-ray photoelectron spectroscopy, are pure stoichiometric ZnS in the hexagonal phase. Surface morphology differs in shape and granule size. During the laser-driven CVD process, gas-phase photochemical intermediates are identified by luminescence spectroscopy. The luminescent photoproducts are Zn and S2, the two elemental components of the final material. Photofragmentation mechanisms leading to ZnS,

4. [Evolutionary Nanomaterials & Nanodevices] Jinwoo Cheon, John Arnold, Kin-Man Yu, Edith D Bourret*
Metalorganic Chemical Vapor Deposition of Semiconducting III/VI In2Se3 Thin Films from the Single-Source Precursor: In [SeC (SiMe3) 3] 3
Chem. Mater., 7(12), 2273-2276
 (Dec 1, 1995)

Thin films of In2Se3 have been prepared by metal-organic chemical vapor deposition (MOCVD) using volatile In [SeC (SiMe3) s] 3 as the precursor. The influence of growth parameters on the formation of crystalline phases and on the morphologies of In2Se3 films were examined by X-ray diffraction and scanning electron microscopy. The stoichiometry of the films was determined by Rutherford backscattering spectroscopy (RBS).

3. [Evolutionary Nanomaterials & Nanodevices] Jinwoo Cheon, Lawrence H Dubois*, Gregory S Girolami*
Chemical Vapor Deposition of Zinc from Diallyl Zinc Precursors
Chem. Mater., 6(12), 2279-2287
 (Dec 1, 1994)

The organometallic compounds bis(allyl)zinc and bis(2-methylallyl)zinc have been shown to serve as MOCVD precursors for the deposition of zinc at temperatures as low as 150 °C. The deposits on Si(100) wafers, quartz, copper, and aluminum consist of aggregates of hexagonal plates and columns. On silicon(100) substrates and at low background pressures (10−4 Torr), the zinc crystals are oriented preferentially with their c axes perpendicular to the silicon surface. The organic byproducts generated under CVD conditions are 1,5- hexadiene (76 mol %), 2-methyl-1,4-pentadiene (14 mol %), and propene (10 mol %); except for the pentadiene product, analogous hydrocarbons in similar amounts are formed when bis(2-methylallyl)zinc is used as the precursor. In situ spectroscopic studies on single-crystal Cud (111) substrates show that bis(allyl)zinc transfers its allyl groups to the surface below 250 °C; the surface-bound allyl groups are probably bound in a trihapto fashion. On clean surfaces, the

List

Copyright and Address

  • ADDRESS Department of Chemistry. 50 Yonsei-ro, Seodaemun-gu, Seoul 03722
  • TEL +82-2-2123-4748
  • FAX +82-2-2123-4640
  • EMAIL lee7626@yonsei.ac.kr
  • © Cheon Group | Yonsei University. All Right Reserved

Display Page Loading Image

Top