• Bulletin of the Korean Chemical Society
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• v.31 no.1
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• pp.112-115
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• 2010

Transparent conducting undoped and Al impurity doped ZnO films were deposited on glass substrate by spin coat technique using 24 days aged ZnO precursor solution with solution of ethanol and diethanolamine. The films were characterized by UV-Visible spectroscopy, X-ray diffraction (XRD), scanning electron microscope (SEM), electrical resistivity ($\rho$), carrier concentration (n), and hall mobility ($\mu$) measurements. XRD data show that the deposited film shows polycrystalline nature with hexagonal wurtzite structure with preferential orientation along (002) crystal plane. The SEM images show that surface morphology, porosity and grain sizes are affected by doping concentration. The Al doped samples show high transmittance and better resistivity. With increasing Al concentration only mild change in optical band gap is observed. Optical properties are not affected by aging of parent solution. A lowest resistivity ($8.5 \times 10^{-2}$ ohm cm) is observed at 2 atomic percent (at.%) Al. With further increase in Al concentration, the resistivity started to increase significantly. The decrease resistivity with increasing Al concentration can be attributed to increase in both carrier concentration and hall mobility.

• Bulletin of the Korean Chemical Society
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• v.35 no.10
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• pp.2974-2978
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• 2014

$Mn_3O_4$/multi-walled carbon nanotube (MWCNT) composites are prepared by chemically synthesizing $Mn_3O_4$ nanoparticles on a MWCNT film at room temperature. Structural and morphological characterization has been carried out using X-ray diffraction (XRD) and scanning and transmission electron microscopies (SEM and TEM). These reveal that polycrystalline $Mn_3O_4$ nanoparticles, with sizes of about 10-20 nm, aggregate to form larger nanoparticles (50-200 nm), and the $Mn_3O_4$ nanoparticles are attached inhomogeneously on MWCNTs. The electrochemical behavior of the composites is analyzed by cyclic voltammetry experiment. The $Mn_3O_4$/MWCNT composite exhibits a specific capacitance of $257Fg^{-1}$ at a scan rate of $5mVs^{-1}$, which is about 3.5 times higher than that of the pure $Mn_3O_4$. Cycle-life tests show that the specific capacitance of the $Mn_3O_4$/MWCNT composite is stable up to 1000 cycles with about 85% capacitance retention, which is better than the pure $Mn_3O_4$ electrode. The improved supercapacitive performance of the $Mn_3O_4$/MWCNT composite electrode can be attributed to the synergistic effects of the $Mn_3O_4$ nanoparticles and the MWCNTs, which arises not only from the combination of pseudocapacitance from $Mn_3O_4$ nanoparticles and electric double layer capacitance from the MWCNTs but also from the increased surface area, pore volume and conducting property of the MWCNT network.

• Korean Journal of Materials Research
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• v.22 no.11
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• pp.609-614
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• 2012

We report on the NO gas sensing properties of non-directional ZnO nanofibers synthesized using a typical electrospinning technique. These non-directional ZnO nanofibers were electrospun on an $SiO_2$/Si substrate from a solution containing poly vinyl alcohol (PVA) and zinc nitrate hexahydrate dissolved in distilled water. Calcination processing of the ZnO/PVA composite nanofibers resulted in a random network of polycrystalline ZnO nanofibers of 50 nm to 100 nm in diameter. The diameter of the nanofibers was found to depend primarily on the solution viscosity; a proper viscosity was maintained by adding PVA to fabricate uniform ZnO nanofibers. Microstructural measurements using scanning electron microscopy revealed that our synthesized ZnO nanofibers after calcination had coarser surface morphology than those before calcination, indicating that the calcination processing was sufficient to remove organic contents. From the gas sensing response measurements for various NO gas concentrations in dry air at several working temperatures, it was found that gas sensors based on electrospun ZnO nanofibers showed quite good responses, exhibiting a maximum sensitivity to NO gas in dry air at an operating temperature of $200^{\circ}C$. In particular, the non-directional electrospun ZnO nanofiber gas sensors were found to have a good NO gas detection limit of sub-ppm levels in dry air. These results illustrate that non-directional electrospun ZnO nanofibers are promising for use in low-cost, high-performance practical NO gas sensors.

• Korean Journal of Materials Research
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• v.20 no.8
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• pp.444-449
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• 2010

Transparent ceramics are used in new technology because of their excellent mechanical properties over glasses. Transparent ceramics are nowadays widely used in armor, laser windows, and in high temperature applications. Silicon nitride ceramics have excellent mechanical properties and if transparent silicon nitride is fabricated, it can be widely used. h-BN has a lubricating property and is ductile. Therefore, adding h-BN to silicon nitride ceramics gives a lubricating property and is also machinable. Translucent silicon nitride was fabricated by hot-press sintering (HPS) and 57% transmittance was observed in the near infrared region. A higher wt. % of h-BN in silicon nitride ceramics does not favor transparency. The optical, mechanical, and tribological properties of BN dispersed polycrystalline $Si_3N_4$ ceramics were affected by the density, ${\alpha}:{\beta}$-phase ratio, and content of h-BN in sintered ceramics. The hot pressed samples were prepared from the mixture of $\alpha-Si_3N_4$, AlN, MgO, and h-BN at $1850^{\circ}C$. The composite contained from 0.25 to 2 wt. % BN powder with sintering aids (9% AlN + 3% MgO). A maximum transmittance of 57% was achieved for the 0.25 wt. % BN doped $Si_3N_4$ ceramics. Fracture toughness increased and wear volume and the friction coefficient decreased with an increase in BN content. The properties such as transmittance, density, hardness, and flexural strength decreased with an increase in content of h-BN in silicon nitride ceramics.

• Journal of Magnetics
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• v.4 no.1
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• pp.33-37
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• 1999

Unidirectional magnetic anisotropy field ($H_an$) was investigated for thin films of $CdCr{2-2x}In_{2X}Se_4 (0$\leq$x$\leq$0.2). This anisotropy originates from the microscopic anisotropic Dzyaloshinskii-Moriya (DM) interaction which arise from the spin-orbit scattering of the conduction electrons by the nonmagnetic impurities. This interaction maintains the remanent magnetization in the direction of the initial applied field. Then the single easy direction of the magnetization is parallel to the direction of the magnetic field. The anisotropy produced by field cooling is unidirectional I.e. the spins system deeps some memory of the cooling field direction. The chalcogenide spinel of$ CdCr_{2-2x}In){2X}Se_4$belongs to the class of the magnetic semiconductors. The magnetic disordered state is obtained when ferromagnetic structure is diluted by In. Then we have the mixed phase characterised by coexistence the magnetic long range ordering (IFN-infinite ferromagnetic network) and the spin glass order (Fc-finite clusters). The total magnetic anisotropy energy depends on the state of magnetic ordering. In our study we concentrated on the magnetic state with reentrant transition and spin glass state. The polycrystalline $ CdCr_{2-2x}In){2X}Se_4$ thin films were obtained by rf sputtering technique. We applied the ferromagnetic resonance (FMR) and M-H loop techniques for determining the temperature composition dependencies of Han. From the experimental data, we have found that Han decreases almost linearly when temperature is increased and in the low temperature is about three times bigger at SG state with comparison to the state with REE.

• Transactions of Materials Processing
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• v.27 no.1
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• pp.48-53
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• 2018

Aluminum nitride (AlN) is used by the semiconductor industry that has requirements for high thermal conductivity. The theoretical thermal conductivity of single crystal AlN is 320W/mK. Whereas, the values measured for polycrystalline AlN ceramics range from 20 W/mK to 280 W/mK. The variability is strongly dependent upon the purity of the starting materials and non-uniform dispersibility of the sintering additive. The conventional AlN sintering additive used yttria ($Y_2O_3$), but the dispersibility of the powder in the mixing process was important. In this study, we investigated the mechanical and thermal conductivity of yttrium nitrate ($Y(NO_3)_3{\cdot}6H_2O$), as a sintering additive in order to improve the dispersibility of $Y_2O_3$. The sintering additives content was in the range of 2 to 4.5wt.%. The density of AlN gradually increased with increasing contents of sintering additive and the flexural strength gradually increased as well. The flexural strength of the sintered body containing 4 wt% of $Y_2O_3$ and $Y(NO_3)_3{\cdot}6H_2O$ was 334.1 MPa and 378.2 MPa, respectively. The thermal conductivities were 189.7W/mK and 209.4W/mK, respectively. In the case of hardness, there was only a slight difference and the average value was about 10 GPa. Therefore, densification, density and strength values were found to be proportional to its content. It was confirmed that AlN using $Y(NO_3)_3{\cdot}6H_2O$ displayed relatively higher thermal conductivity and mechanical properties than the $Y_2O_3$.

• Korean Journal of Materials Research
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• v.8 no.2
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• pp.147-153
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• 1998

Tungsten nitride is very attractive as absorber for X-ray lithographic mask and as a diffusion barrier for interconnecting metallization in Si VLSI technology. Microstructure of tungsten nitride films prepared by RF magnetron sputtering has been investigated as a function of deposition parameter. The crystal structure of sputtered films on silicon nitride membrane depends strongly on the NJAr gas flow ratio(0~18%1, gas pressure(l0~43mTorr). RF power (60~150W), target-substrate distance(4~8cm). Tungsten nitride films deposited at the $N_2/Ar$ gas flow ratio(- 10%). gas pressure(~10mmTorr), RF power(~150W) and target-substrate distance(6cm) are amorphous, but at other conditions are almost rough -surfaced polycrystalline. Amorphous films are very smooth($3.1\AA$ rms) and expected to be excellent absorber for X-ray mask.

• Journal of Microbiology and Biotechnology
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• v.28 no.8
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• pp.1367-1375
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• 2018

Silver nanoparticles have been widely applied for biomedical areas owing to their potent antiviral and antibacterial activities. Synthesis of silver nanoparticles using biomacromolecules is more efficient, environment-friendly, and cost-saving compared with the traditional approach. In this paper, a novel approach was developed to establish a reaction system with $Ag^+-BH4^--sericin$ to synthesize silver nanoparticles conjugated to sericin (AgNPs-Sericin). Sericin could be as a good dispersant and stabilizing agent, which is able to modify nanoscaled AgNPs, the average diameter of which was only $3.78{\pm}1.14nm$ prepared in a 0.3 mg/ml sericin solution. The characterizations of the AgNPs-Sericin were determined by FTIR, thermogravimetry, and XRD analyses. The results showed that the synthesized AgNPs conjugated with sericin as organic phase. Via SAED and XRD analysis, we showed that these AgNPs formed polycrystalline powder with a face-centered cubic structure of bulk metals. Moreover, we investigated the antiviral and antibacterial activities of AgNPs-Sericin, and the results showed that AgNPs-Sericin exhibited potent anti-HIV-1 activity against CCR5-tropic and CXCR4-tropic strains, but no significant cytotoxicity was found toward human genital epithelial cells compared with free silver ions, which are accepted as a commonly used potent antimicrobial agent. Moreover, its antibacterial activity was determined via flow cytometry. The results showed that AgNPs-Sericin could suppress gram-negative (E. coli) and gram-positive (S. aureus) bacteria, but more was potent for the gram-negative one. We concluded that our AgNPs-Sericin could be a potential candidate as a microbicide or antimicrobial agent to prevent sexually transmitted infections.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.9 no.3
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• pp.280-285
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• 1999

$\alpha$-$Fe_2O_3$ thin film gas sensors were deposited at various temperature by CVD method. Polycrystalline $\alpha$-$Fe_2O_3$ thin films were deposited at $175^{\circ}C$ and $200^{\circ}C$. $\gamma$-$\alpha$-$Fe_2O_3$ phase was obtained when the deposition temperature was higher than $250^{\circ}C$. The crystallite size of $\alpha$-$Fe_2O_3$ was affected by the deposition and annealing temperature. The specimen deposited at $175^{\circ}C$ showed maximum sensitivity. In this condition, the sensitivity of $\alpha$-$Fe_2O_3$ thin film for NO gas (at 250 ppm) was 3.2 and response time (at 100ppm) was 12 second.

• Journal of the Korean Chemical Society
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• v.31 no.1
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• pp.102-109
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• 1987

Some characteristics of $SnO_2$ film which was deposited on a slide glass substrate, using dibutyl tin diacetate and oxygen, by the chemical vapor deposition were observed. The optimum condition for the preparation of the film was found to be at 420$^{\circ}C$ of substrate temperature for 20 min of deposition. Important optical, electrical, and structural features of the film were examined. It was found that the typical $SnO_2$ film on the untreated substrate was 4000${\AA}$ in thickness, transmitted 90% of the visible liglit, and provided 5800 ohms/${\square}$ of the sheet resistance. It was also found that the surface treatments of the slide glass by acid leaching were beneficial. The film structure was found to be a mixture of polycrystalline tetragonal stannic oxide confirmed by the X-ray diffraction and to be spherical fine grains concluded by the scanning electron microscopy.