Jong Keun Ha

Consideration of Fe Nanoparticles and Nanowires Synthesized by Chemical Vapor Condensation Process

Various physical, chemical and mechanical methods, such as inert gas condensation, chemical vapor condensation, sol-gel, pulsed wire evaporation, evaporation technique, and mechanical alloying have been used to synthesize nanoparticles. Among them, chemical vapor condensation(CVC) represents the benefit for its applicability to almost materials because a wide range of precursors are available for large-scale production with a non-agglomerated state. In this work, iron nanoparticles and nanowires have synthesized by chemical vapor condensation(CVC) process, using iron pentacarbonyl(Fe(CO)5) as precursor. The effects of processing parameters on the morphology, microstructure and size of iron nanoparticles and nanowires were studied. Iron nanoparticles and nanowires having various diameters were obtained by controlling the inflow of metallic organic precursor. Both nanoparticles and nanowires were crystallized. Characterization of obtained nanoparticles and nanowires were investigated by using a field emission scanning electron microscopy, transmission microscopy and X-ray diffraction.

Physical and electrochemical properties of synthesized carbon nanotubes [CNTs] on a metal substrate by thermal chemical vapor deposition

Multi-walled carbon nanotubes were synthesized on a Ni/Au/Ti substrate using a thermal chemical vapor deposition process. A Ni layer was used as a catalyst, and an Au layer was applied as a barrier in order to prevent diffusion between Ni and Ti within the substrate during the growth of carbon nanotubes. The results showed that vertically aligned multi-walled carbon nanotubes could be uniformly grown on the Ti substrate (i.e., metal substrate), thus indicating that the Au buffer layer effectively prevented interdiffusion of the catalyst and metal substrate. Synthesized carbon nanotubes on the Ti substrate have the diameter of about 80 to 120 nm and the length of about 5 to 10 μm. The Ti substrate, with carbon nanotubes, was prepared as an electrode for a lithium rechargeable battery, and its electrochemical properties were investigated. In a Li/CNT cell with carbon nanotubes on a 60-nm Au buffer layer, the first discharge capacity and discharge capacity after the 50th cycle were 210 and 80 μAh/cm2, respectively.

Characterization of Fe-Mo Alloyed Nanoparticles Synthesized by Chemical Vapor Condensation Process

Iron(Fe)-molybdenum(Mo) alloyed nanopaticles and nanowires were produced by the chemical vapor condensation(CVC) process using the pyrolysis of iron pentacarbonyl(Fe(CO)5) and molybdenum hexacarbonyl(Mo(CO)6). The influence of CVC parameter on the formation of nanoparticle, nanowire and size control was studied. The size of Fe-Mo alloyed nanoparticles can be controlled by quantity of gas flow. Also, Fe-Mo alloyed nanowires were produced by control of the work chamber pressure. Obtained nanoparticles and nanowires were investigated by field emission scanning electron microscopy, transmission electron microscopy and X-ray diffraction.

Structure and Electrochemical Properties of FeSx Nanoparticles Synthesized by Chemical Vapor Condensation Process

FeSx nanoparticles were synthesized by the chemical vapor condensation (CVC) process using the pyrolysis of iron pentacarbonyl (Fe(CO)5) and sulfur (S). The influence of CVC parameter on the formation of nanoparticle and size distribution was studied. The synthesized nanoparticles consisting of FeS, FeS2 and Fe2O3 were nearly spherical shape and 5~40 nm in mean diameter. Obtained particles were studied by applying the field emission scanning electron microscopy (FESEM) and high resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD) methods. Electrochemical properties of the electrode fabricated with synthesized nanoparticles were evaluated.

New approach to synthesis of carbon nanotubes

Carbon nanotubes (CNTs) have been synthesized through chemical vapor deposition in argon gas atmosphere using Fe–2.5%Mo alloyed nanoparticles as a catalyst and H2/CH4 gas mixture as a reaction gas. Fe–2.5 wt.%Mo alloyed nanoparticles with average diameter of 7, 20, 45 and 85 nm are prepared by the chemical vapor condensation process using the pyrolysis of iron pentacarbonyl (Fe(CO)5) and molybdenum hexacarbonyl (Mo(CO)6). The morphologies of the CNTs are controlled by adjusting the nanoparticle size, reaction gas ratio and reaction temperature. With decreasing nanoparticle size under the same experimental conditions, the degree of crystalline perfection increases gradually and the morphologies of the carbon nanotubes vary from multi wall carbon nanotubes to single wall carbon nanotubes. Also, the ratio of reaction gas has an effect on the morphology and the degree of crystallinity of CNTs. In this work, it is suggested that morphology, diameter and degree of crystallinity of CNTs could be controlled by adjusting the reaction gas ratio, reaction temperature and catalyst size.

Preparation of Amorphous Silicon Oxide Nanowires by the Thermal Heating of Ni or Au-Coated Si Substrates

Silicon oxide (SiOx) nanowires may have many applications due to their electrical, mechanical and optical properties. Many methods have been reported for the synthesis of SiOx nanowires, including laser ablation, sol–gel, thermal evaporation, carbothermal reduction, physical evaporation, rapid thermal annealing, chemical vapor deposition and thermal oxidation route, oxide assisted growth and thermal sublimation. In this paper, we reported SiOx nanowires fabricated by simple thermal heating process of catalyst thin film-coated Si substrates with various parameters, such as synthesis temperature, synthesis gases, catalysts, and buffer layer (SiO2 layer). Synthesized silicon oxide nanowires were amorphous crystalline. The best synthesis condition of prepared SiOx nanowire is slightly varied with catalysts and buffer layer. The flow rate of synthesis gas affected diameter of silicon oxide nanowires.