• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.440-440
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• 2012

Nanomaterials have emerged as new building blocks to construct light energy harvesting assemblies. Size dependent properties provide the basis for developing new and effective systems with semiconductor nanoparticles, quantized charging effects in metal nanoparticle or their combinations in 2 and 3 dimensions for expanding the possibility of developing new strategies for photovoltaic system. As top-down approach, we developed a simple and effective method for the large scale formation of self-assembled Cu(In,Ga)$Se_2$ (CIGS) nanostructures by ion beam irradiation. The compositional changes and morphological evolution were observed as a function of the irradiation time. As the ion irradiation time increased, the nano-dots were transformed into a nano-ridge structure due to the difference in the sputtering yields and diffusion rates of each element and the competition between sputtering and diffusion processes during irradiation. As bottom-up approach, we developed the growth of CIGS nanowires using thermal-chemical vapor deposition (CVD) method. Vapor-phase synthesis is probably the most extensively explored approach to the formation of 1D nanostructures such as whiskers, nanorods, and nanowires. However, unlike binary or ternary chalcogenides, the synthesis of quaternary CIGS nanostructures is challenging because of the difficulty in controlling the stoichiometry and phase structure. We introduced a method for synthesis of the single crystalline CIGS nanowires in the form of chalcopyrite using thermal-CVD without catalyst. It was confirmed that the CIGS nanowires are epitaxially grown on a sapphire substrate, having a length ranged from 3 to 100 micrometers and a diameter from 30 to 500 nm.

• Bulletin of the Korean Chemical Society
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• v.29 no.8
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• pp.1491-1494
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• 2008

A novel platinum aminoalkoxide complex, Pt$(dmamp)_2$ has been prepared by the reaction of cis-$(py)_2PtI_2$ with two equivalents of Na(dmamp) (dmamp = 1-dimethylamino-2-methyl-2-propanolate). Single-crystal X-ray crystallographic analysis shows that the Pt(dmamp)2 complex keeps a square planar geometry with each two nitrogen atoms and two oxygen atoms having trans configuration. Platinum films have been deposited on TaN/ Ta/Si substrates by metal organic chemical vapor deposition (MOCVD) using Pt$(dmamp)_2$. As-deposited platinum thin films did not contain any appreciable amounts of impurities except a little carbon. As the deposition temperature was increased, the films resistivity and deposition rate increased. The electrical resistivity (13.6 $\mu\Omega$cm) of Pt film deposited at 400 ${^{\circ}C}$ is a little higher than the bulk value (10.5 $\mu\Omega$cm) at 293 K. The chemical composition, crystalline structure, and morphology of the deposited films were investigated by X-ray photoelectron spectroscopy, X-ray diffraction, and atomic force microscopy.

• Journal of Magnetics
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• v.19 no.1
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• pp.59-63
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• 2014

Nano-sized nickel substituted cobalt ferrite powders, $Ni_xCo_{1-x}Fe_2O_4$ ($0.0{\leq}x{\leq}1.0$), were fabricated by the sol-gel method, and their crystallographic and magnetic properties were studied. All the ferrite powders showed a single spinel structure, and behaved ferrimagnetically. When the nickel substitution was increased, the lattice constants and the sizes of particles of the ferrite powders decreased. The M$\ddot{o}$ssbauer absorption spectra of $Ni_xCo_{1-x}Fe_2O_4$ ferrite powders could be fitted with two six-line subspectra, which were assigned to a tetrahedral A-site and octahedral B-sites of a typical spinel crystal structure. The increase in values of the magnetic hyperfine fields indicated that the superexchange interaction was stronger, with the increased nickel concentration in $Ni_xCo_{1-x}Fe_2O_4$. This could be explained using the cation distribution, which can be written as, $(Co_{0.28-0.28x}Fe_{0.72+0.28x})[Ni_xCo_{0.72-0.72x}Fe_{1.28-0.28x}]O_4$. The two values of the saturation magnetization and the coercivity decreased, as the rate of nickel substitution was increased. These decreases could be explained using the cation distribution, the magnetic moment, and the magneto crystalline anisotropy constant of the substituted ions.

• Korean Journal of Materials Research
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• v.19 no.11
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• pp.631-636
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• 2009

We investigated the NO gas sensing characteristics of ZnO-carbon nanotube (ZnO-CNT) layered composites fabricated by coaxial coating of single-walled CNTs with a thin layer of 1 wt% Al-doped ZnO using rf magnetron sputtering deposition. Morphological studies clearly revealed that the ZnO appeared to form beadshaped crystalline nanoparticles with an average diameter as small as 30 nm, attaching to the surface of the nanotubes. It was found that the NO gas sensing properties of the ZnO-CNT layered composites were dramatically improved over Al-doped ZnO thin films. It is reasoned from these observations that an increase in the surface-to-volume ratio associated with the numerous ZnO “nanobeads” on the surface of the CNTs results in the enhancement of the NO gas sensing properties. The ZnO-CNT layered composite sensors exhibited a maximum sensitivity of 13.7 to 2 ppm NO gas at a temperature of 200${^{\circ}C}$ and a low NO gas detection limit of 0.2 ppm in dry air.

• Journal of the Institute of Electronics Engineers of Korea TE
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• v.39 no.1
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• pp.31-36
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• 2002

Low energy boron ions were implanted into the preamorphized and crystalline silicon substrates to form 0.2${\mu}m$ $p^+-n$ junctions. The rapid thermal annealing(RTA) was used to annihilate the crystal defects due to implantation and to activate the implanted boron ions, and the furnace annealing was employed to reflow the BPSG(bolo-phosphosilicate glass). The implantation conditions for Gepreamorphization were the energy of 45keV and the dose of 3$\times$1014cm-2. BF2 ions employed as a p-type dopant were implanted with the energy of 20keV and the dose of 2$\times$1015cm-2. The thermal conditions of RTA and furnace annealing were $1000^{\circ}C$/10sec and $850^{\circ}C$/40min, respectively. The junction depths were measured by SIMS and ASR techniques, and the 4-point probe was used to measure the sheet resistances. The electrical characteristics were analyzed via the leakage currents of the fabricated diodes. The single thermal processing with RTA produced shallow junctions of good qualities, and the thermal treatment sequence of furnace anneal and RTA yielded better junction characteristics than that of RTA and furnace anneal.

• Journal of the Korean Ceramic Society
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• v.39 no.1
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• pp.74-78
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• 2002

In this study, the solution combustion method was employed to synthesize perovskite PZT ceramics. Multicomponent oxides can be prepared by the solution combustion synthesis using redox exothermic reaction of precursor solutions. The results of DTA/TG showed exothermic peaks in 214$^{\circ}C$ and 350$^{\circ}C$. Those were caused by the differences of the thermal decomposition behavior of oxidizer and fuel. The combustion reaction was completed at 370$^{\circ}C$ during heating procedure, but the product was not transformed into perovskite. The thermal decomposition behavior of both oxidizer and fuel were considered during solution combustion process at 600$^{\circ}C$, which showed tetragonal single phase PZT ceramics with 50 nm crystalline size. The lattice constant a was 3.997 ${\pm}$ 0.001 ${\AA}$ and the lattice constant c was 4.147${\pm}$0.001 ${\AA}$.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.7 no.1
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• pp.47-58
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• 1997

In this study single crystalline corundum ($\alpha$-$Al_2O_3$) powders were prepared from gibbsite using hydrothermal growing processes. Addition of a mineralizer and the characteristics of solid substances were investigated to find their effects on the size distribution and crystalllnity of products. Experimental results showed that as the concentration of potassium hydroxide (KOH), a mineralizer, the particle size of corundum powders became larger at lower reaction temperatures. However, the size of corundum powders became smaller as the concentration of gibbsite increased in the feedstock. The hydrothermal synthetic conditions are also strongly dependent on the properties of hydrothermal solutions. Corundum powders which have the weight mean particle size of 1~10 $\mu\textrm{m}$ with shapes of hexagonal were prepared in this experiment.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.10a
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• pp.30.1-30.1
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• 2011

Silicon is one of useful materials in various industry such as semiconductor, solar cell, and secondary battery. The metallic silicon produces generally melting process for ingot type or chemical vapor deposition (CVD) for thin film type. However, these methods have disadvantages of high cost, complicated process, and consumption of much energy. Electrodeposition has been known as a powerful synthesis method for obtaining metallic species by relatively simple operation with current and voltage control. Unfortunately, the electrodeposition of the silicon is impossible in aqueous electrolyte solution due to its low oxidation-reduction equilibrium potential. Ionic liquids are simply defined as ionic melts with a melting point below $100^{\circ}C$. Characteristics of the ionic liquids are high ionic conductivities, low vapour pressures, chemical stability, and wide electrochemical windows. The ionic liquids enable the electrochemically active elements, such as silicon, titanium, and aluminum, to be reduced to their metallic states without vigorous hydrogen gas evolution. In this study, the electrodeposion of silicon has been investigated in ionic liquid of 1-butyl-3-methylpyrolidinium bis (trifluoromethylsulfonyl) imide ([bmpy]$Tf_2N$) saturated with $SiCl_4$ at room temperature. Also, the effect of electrode materials on the electrodeposition and morphological characteristics of the silicon electrodeposited were analyzed The silicon electrodeposited on gold substrate was composed of the metallic Si with single crystalline size between 100~200nm. The silicon content by XPS analysis was detected in 31.3 wt% and the others were oxygen, gold, and carbon. The oxygen was detected much in edge area of th electrode due to $SiO_2$ from a partial oxidation of the metallic Si.

• Korean Journal of Materials Research
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• v.20 no.4
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• pp.199-203
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• 2010

Hybridization of semiconductor materials with carbon nanotubes (CNTs) is a recent field of interest in which new nanodevice fabrication and applications are expected. In this work, nanowire type GaAs structures are synthesized on porous single-wall carbon nanotubes (SWCNTs) as templates using the molecular beam epitaxy (MBE) technique. The field emission properties of the as-synthesized products were investigated to suggest their potential applications as cold electron sources, as well. The SWCNT template was synthesized by the arc-discharge method. SWCNT samples were heat-treated at $400^{\circ}C$ under an $N_2/O_2$ atmosphere to remove amorphous carbon. After heat treatment, GaAs was grown on the SWCNT template. The growth conditions of the GaAs in the MBE system were set by changing the growth temperatures from $400^{\circ}C$ to $600^{\circ}C$. The morphology of the GaAs synthesized on the SWCNTs strongly depends on the substrate temperature. Namely, nano-crystalline beads of GaAs are formed on the CNTs under $500^{\circ}C$, while nanowire structures begin to form on the beads above $600^{\circ}C$. The crystal qualities of GaAs and SWCNT were examined by X-ray diffraction and Raman spectra. The field emission properties of the synthesized GaAs nanowires were also investigated and a low turn-on field of $2.0\;V/{\mu}m$ was achieved. But, the turn-on field was increased in the second and third measurements. It is thought that arsenic atoms were evaporated during the measurement of the field emission.

• Korean Journal of Materials Research
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• v.18 no.11
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• pp.623-627
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• 2008

For possible applications as luminescent materials for white-light emission using UV-LEDs, $Ba_2Mg(PO_4)_2:Eu^{2+}$ phosphors were prepared by a solid state reaction. The photoluminescence properties of the phosphor were investigated under ultraviolet ray (UV) excitation. The prepared phosphor powders were characterized to from a single phase of a monoclinic crystalline structure by a powder X-ray diffraction analysis. In the photoluminescence spectra, the $Ba_2Mg(PO_4)_2:Eu^{2+}$ phosphor showed an intense emission band centered at the 584 nm wavelength due to the f-d transition of the $Eu^{2+}$ activator. The optimum concentration of $Eu^{2+}$ activator in the $Ba_2Mg(PO_4)_2$ host, indicating the maximum emission intensity under the excitation of a 395 nm wavelength, was 5 at%. In addition, it was confirmed that the $Eu^{2+}$ ions are substituted at both $Ba^{2+}$ sites in the $Ba_2Mg(PO_4)_2$ crystal. On the other hand, the critical distance of energy transfer between $Eu^{2+}$ ions in the $Ba_2Mg(PO_4)_2$ host was evaluated to be approximately 19.3 A. With increasing temperature, the emission intensity of the $Ba_2Mg(PO_4)_2$:Eu phosphor was considerably decreased and the central wavelength of the emission peak was shifted toward a short wavelength.