• Applied Chemistry for Engineering
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• v.19 no.3
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• pp.270-276
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• 2008

$N_2$ doped $TiO_2$ nano-sized powder was prepared using a DC arc plasma jet and investigated with XRD, BET, SEM, TEM, and photo-catalytic decomposition. Recently the research interest about the nano-sized $TiO_2$ powder has been increased to improve its photo-catalytic activity for the removal of environmental pollutants. Nitrogen gas, reacting gas, and titanium tetrachloride ($TiCl_4$) were used as the raw materials and injected into the plasma reactor to synthesize the $N_2$ doped $TiO_2$ power. The particle size and XRD peaks of the synthesized powder were analyzed as a function of the flow rate of the nitrogen gas. Also, the characteristics of the photo-catalytic decomposition using the prepared powder were studied. For comparing the photo-catalytic decomposition performance of $TiO_2$ powder with that of $TiO_2$ coating, $TiO_2$ thin films were prepared by the spin coating and the pulsed laser deposition. For the results of the acetaldehyde decomposition, the photo-catalytic activity of $TiO_{2-x}N_x$ powder was higher than that of the pure $TiO_2$ powder in the visible light region. For the methylene blue decomposition, the decomposition efficiency of $TiO_2$ powder was also higher than that of $TiO_2$ film.

• Clean Technology
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• v.28 no.3
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• pp.210-217
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• 2022

Boron(B) is a rare resource used for various purposes such as glass, semiconductor materials, gunpowder, rocket fuel, etc. However, Korea depends entirely on imports for boron. Considering the global boron reserves and its current production rate, boron will be depleted on earth in 50 years. Thus, a process including proper adsorbent materials recovering boron from seawater is demanded. This research proposed carbonized nanofibers prepared from electrospun PAN(polyacrylonitrile) mats as promising materials to adsorb boron in aqueous solution. First, the mechanism of boron adsorption on carbonized nanofibers was investigated by DFT(density functional method)-based molecular modeling and the calculated energetics demonstrated that the boron chemisorption on the nitrogen-doped graphene surface by a two-step dehydration is possible with viable activation energies. Then, the electrospun PAN mats were stabilized in air and then carbonized in an argon atmosphere before being immersed in the boric acid aqueous solution. Analytically, SEM(scanning electron microscopy) and Raman measurements were employed to confirm whether the electrospinning and carbonization of PAN mats proceeded successfully. Then, XPS(X-ray photoelectron spectroscopy) peak analysis showed whether the intended nitrogen-doped carbon nanofiber surface was formed and boron was properly adsorbed on nanofibers. Those results demonstrated that the carbonized nanofibers prepared from electrospun PAN mats could be feasible adsorbents for boron recovery in seawater.

• Applied Chemistry for Engineering
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• v.25 no.3
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• pp.292-299
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• 2014

In this study, nitrogen doped carbon felt (CFt) is prepared using thermal oxidation and liquid phase ammonia treatment to improve the efficiency for vanadium redox flow batteries (VRFB). The electrochemical properties of prepared CFt electrodes are investigated using cyclic voltammetry (CV) and charge/discharge test. The XPS result shows that the increase of liquid phase ammonia treatment temperature leads to the increased nitrogen functional group on the CFt surface. Redox reaction characteristics using CV reveal that the liquid phase ammonia treated CFt electrodes are more reversible than the thermally oxidized CFt. When CFt is treated by the liquid phase ammonia at $300^{\circ}C$, VRFB cell energy efficiency, voltage efficiency, and current efficiency are increased about 6.93%, 1.0%, and 4.5%, respectively, compared to those of the thermally oxidized CFt. These results are because nitrogen functional groups on CFt help to improve the electrochemical properties of redox reaction between electrode and electrolyte interface.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.32 no.2
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• pp.55-60
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• 2022

In this study, a heat treatment experiment was conducted to select a new melt composition that can easily control the unintentionally doped nitrogen (N-UID) without degrading the SiC single crystal quality during TSSG process. The experiment was carried out for about 2 hours at a temperature of 1900℃ under Ar atmosphere. The used melt composition is based on either Si-Ti 10 at% or Si-Cr 30 at%, and also Co or Sc transition metals, which are effective for carbon solubility, were added at 3 at%, respectively. After the experiment, the crucible was cross-sectionally cut, and evaluated the Si-C reaction layer on the crucible-melt interface. As a result, with Sc addition, Si-C reaction layers uniformly occurred with a Si-infiltrated layer (~550 ㎛) and a SiC interlayer (~23 ㎛). This result represented that the addition of Sc is an effective transition metal with high carbon solubility and can feed carbon sources into the melt homogeneously. In addition, Sc is well known to have low reactivity energy with nitrogen compared to other transition metals. Therefore, we expect that both growth rate and Nitrogen UID can be controlled by Si-Sc based melt in the TSSG process.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.31 no.1
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• pp.32-36
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• 2021

This study was investigated in carbon diffusion behavior of laser-carburized TiZrN coating layer and the changes of mechanical properties. The carbon paste was deposited on TiZrN coatings, and the laser was irradiated to carburize into the coatings. The XRD peak corresponding to the (111) plane shifted to a lower angle after the carburization, showing the lattice expansion by doped carbon. The decreased grain size implied the compression by the grain boundary diffusion of carbon. The XPS spectra for the bonding states of carbon was analyzed that carbon was substitute to nitrogen atoms in TiZrN, as carbide, through the thermal energy of laser. In addition, the combination of sp2 and sp3 hybridized bonds represented the formation of an amorphous carbon. The cross-sectional TEM image and the inverse FFT of the TiZrN coating after carburizing were observed as the wavy shape, confirming the amorphous phase located in grain boundaries. After the carburization, the hardness increased from 34.57 GPa to 38.24 GPa, and the friction coefficient decreased by 83 %. In particular, the ratio of hardness and elastic modulus (H/E) which is used as an index of the elastic recovery, increased from 0.11 to 0.15 and the wear rate improved by 65 %.

• Journal of the Microelectronics and Packaging Society
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• v.22 no.4
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• pp.111-115
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• 2015

To improve the efficiency of the Si solar cell, high minority carrier life time is required. Therefore, the passivation technology is important to eliminate point defects on the silicon surface, causing the loss of minority carrier recombination. PECVD or post-annealing of thermally-grown $SiO_2$ is commonly used to form the passivation layer, but a high-temperature process and low thermal stability is a critical factor of low minority carrier lifetime. In this study, atomic layer deposition was used to grow the $Al_2O_3$ passivation layer at low temperature process. $Al_2O_3$ was selected as a passivation layer which has a low surface recombination velocity because of the fixed charge density. For the high charge density, an improved minority carrier lifetime, and a low surface recombination, nitrogen was doped in the $Al_2O_3$ thin film and the improvement of passivation was studied.

• Proceedings of the Materials Research Society of Korea Conference
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• 1999.11a
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• pp.76-76
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• 1999

Low resistance ohmic contacts to the Si-doped InGaN(~$\times$10$^{19}$ ㎤) were obtained using the W metallization schemes. Specific contact resistance decreased with increasing annealing temperature. The lowest resistance is obtained after a nitrogen ambient annealing at 95$0^{\circ}C$ for 90s, which results in a specific contact resistance of 2.75$\times$10$^{-8}$ Ω$\textrm{cm}^2$. Interfacial reactions and surface are analyzed using x-ray diffraction, transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The X-ray diffraction results show that the reactions between the W film and the InGaN produce a $\beta$-W$_2$N phase at the interface. TEM results also show that the $\beta$-W$_2$N has a rough interface, which increase contact area. It shows that the morphology of the contacts is stable up to a temperature as high as 95$0^{\circ}C$. Possible mechanisms are proposed to describe the annealing temperature dependence of the specific contact resistance.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.13 no.5
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• pp.205-210
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• 2003

Alexandrite-like cubic zirconia single crystals were grown by skull melting method. The R.F. generator (output power is 35 ㎾) used for skull melting was operated at 2 MHz. The grown crystals were doped with up to 1 or 1.5 wt% and 0.5 or 1 wt% of rare earth metal ion (Pr, Nd) on$ ZrO_2-Y_2O_3$ (12 mol%). The grown crystals were cut for slice (0.25 mm) and round brilliant (12 mm in diameter). The cut stones were heat treated in air and nitrogen at $1000^{\circ}C$ for 2 hours and their optical absorption spectra ($\lambda$ = 400∼700 nm) data were obtained.

• Journal of the Korean Vacuum Society
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• v.6 no.S1
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• pp.47-52
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• 1997

Metastable pseudomorphic GeSi layers grown by vapor phase epitaxy on Si(100) substrates were implanted at room temperature. The implantations were performed with 90 KeV As ions to a dose of $1\times 10^{13}\;\textrm{cm}^2$ for $Ge_{0.08}Si_{0.92}$ layers and 709 keV $BF_2^+$ ions to a dose of $3\times 10^{13}\;\textrm{cm}^2$ for $Ge_{0.06}Si_{0.94}$layers. The samples were subsequently annealed for short 10-40 s durations in a lamp furnace with a nitrogen ambient or for a long 30 min period in a vacuum tube furnace. For $Ge_{0.08}Si_{0.92}$samples annealed for a 30 min-longt duration at $700^{\circ}C$ the dopant activation can only reach 50% without introducing significant strain relaxaion whereas samples annealed for short 40s periods (at $850^{\circ}C$) can achieve more than 90% activation without a loss of strain, For $Ge_{0.06}Si_{0.94}$samples annealed for either 40s or 30min at $800^{\circ}C$ full electrical activation of the boron is exhibited in the GeSi epilayer without losing their strain. However when annealed at $900^{\circ}C$ the strain in both implanted and unimplanted layers is partly relaxed after 30min whereas it is not visibly relaxed after 40s.

• Korean Journal of Crystallography
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• v.11 no.1
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• pp.16-21
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• 2000

(Yb/sub x/Y/sub 1-x/)Ca₄O(BO₃)₃ single crystals where x=0.3,8,15,20% were grown by Czochralski Method. The crystals grown under the optimum conditions were transparent and colorless with good crystal form. Using polarizing microscope, crystal defects such as parasite crystals and bubbles were detected depending on the composition of melts and pulling rates. The optimum growth parameters for high quality of single crystals were 15∼20 rpm of rotation rate and 2mm/h of pulling rate at the flow rate of 2 l/min of Nitrogen gas. The relationship between crystal axes and optical axes was investigated by optical crystallographic method, polarization technique and single crystal X-ray method. From the spectroscopic measurements, it was confirmed that there were strong absorption bands at 900 and 976.4 nm and strong emission band at 976.4 nm in Yb/sup 3+/ ion doped YCa₄O(BO₃)₃ crystal. For the application of second harmonic generation of 1.064 ㎛ laser, non-linear optical devices with θ=32.32° and Ψ=0°, λ/10 of flatness and the size of 6x8x5.73 mm were fabricated from the grown YCa₄O(BO₃)₃ crystal.