• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.32 no.5
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• pp.376-381
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• 2019

In this work, we evaluated the structural, electrical and optical properties of $Ge_8Sb_2Te_{11}$ and Cu-doped $Ge_8Sb_2Te_{11}$ thin films prepared by rf-magnetron reactive sputtering. The 200-nm-thick deposited films were annealed in a range of $100{\sim}400^{\circ}C$ using a furnace in an $N_2$ atmosphere. The amorphous-to-crystalline phase changes of the thin films were investigated by X-ray diffraction (XRD), UV-Vis-IR spectrophotometry, a 4-point probe, and a source meter. A one-step phase transformation from amorphous to face-centered-cubic (fcc) and an increase of the crystallization temperature ($T_c$) was observed in the Cu-doped film, which indicates an enhanced thermal stability in the amorphous state. The difference in the optical energy band gap ($E_{op}$) between the amorphous and crystalline phases was relatively large, approximately 0.38~0.41 eV, which is beneficial for reducing the noise in the memory devices. The sheet resistance($R_s$) of the amorphous phase in the Cu-doped film was about 1.5 orders larger than that in undoped film. A large $R_s$ in the amorphous phase will reduce the programming current in the memory device. An increase of threshold voltage ($V_{th}$) was seen in the Cu-doped film, which implied a high thermal efficiency. This suggests that the Cu-doped $Ge_8Sb_2Te_{11}$ thin film is a good candidate for PRAM.

• Korean Journal of Materials Research
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• v.29 no.8
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• pp.491-496
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• 2019

In this study, we prepare pure $WO_3$ inverse opal(IO) film with a thickness of approximately $3{\mu}m$ by electrodeposition, and an ultra-thin $TiO_2$ layer having a thickness of 2 nm is deposited on $WO_3$ IO film by atomic layer deposition. Both sets of photoelectrochemical properties are evaluated after developing dye-sensitized solar cells(DSSCs). In addition, morphological, crystalline and optical properties of the developed films are evaluated through field-emission scanning electron microscopy(FE-SEM), High-resolution transmission electron microscopy(HR-TEM), X-ray diffraction(XRD) and UV/visible/infrared spectrophotometry. In particular, pure $WO_3$ IO based DSSCs show low $V_{OC}$, $J_{SC}$ and fill factor of 0.25 V, $0.89mA/cm^2$ and 18.9 %, achieving an efficiency of 0.04 %, whereas the $TiO_2/WO_3$ IO based DSSCs exhibit $V_{OC}$, $J_{SC}$ and fill factor of 0.57 V, $1.18mA/cm^2$ and 50.1 %, revealing an overall conversion efficiency of 0.34 %, probably attributable to the high dye adsorption and suppressed charge recombination reaction.

• Korean Journal of Metals and Materials
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• v.46 no.2
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• pp.88-96
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• 2008

Thermal evaporated 10 nm-$Ni_{50}Co_{50}$/(70 nm-poly)Si films were deposited to examine the energy saving properties of silicides formed by rapid thermal annealing at temperature ranging from 500 to $1,100^{\circ}C$ for 40 seconds. Thermal evaporated 10 nm-Ni/(70 nm-poly)Si films were also deposited as a reference using the same method for depositing the 10 nm-$Ni_{50}Co_{50}$/(70 nm-poly)Si films. A four-point probe was used to examine the sheet resistance. Transmission electron microscopy (TEM) and X-ray diffraction XRD were used to determine cross sectional microstructure and phase changes, respectively. UV-VIS-NIR and FT-IR (Fourier transform infrared spectroscopy) were used to examine the near-infrared (NIR) and middle-infrared (MIR) absorbance. TEM analysis confirmed that the uniform nickel-cobalt composite silicide layers approximately 21 to 55 nm in thickness had formed on the single and polycrystalline silicon substrates as well as on the 25 to 100 nm thick nickel silicide layers. In particular, nickel-cobalt composite silicides showed a low sheet resistance, even after rapid annealing at $1,100^{\circ}C$. Nickel-cobalt composite silicide and nickel silicide films on the single silicon substrates showed similar absorbance in the near-IR region, while those on the polycrystalline silicon substrates showed excellent absorbance until the 1,750 nm region. Silicides on polycrystalline substrates showed high absorbance in the middle IR region. Nickel-cobalt composite silicides on the poly-Si substrates annealed at $1,000^{\circ}C$ superior IR absorption on both NIR and MIR region. These results suggest that the newly proposed $Ni_{50}Co_{50}$ composite silicides may be suitable for applications of IR absorption coatings.

• Advances in nano research
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• v.10 no.2
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• pp.191-210
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• 2021

To compare the antifungal effect of two nanomaterials (NMs), nanoparticles of zinc oxide were synthesized by a chemical route and zinc oxide-based nanobiohybrids were obtained using green synthesis in an extract of garlic (Allium sativum). The techniques of X-Ray Diffraction (XRD), Infrared (IR) and Ultraviolet Visible (UV-Vis) absorption spectroscopies and Scanning (SEM) and Transmission Electron Microscopies (TEM) were used to determine the characteristics of the nanomaterials synthesized. The results showed that the samples obtained were of nanometric size (< 100 nm). To compare their antifungal capacity, their effect on Cercospora sp. was evaluated. Test results showed that both nanomaterials had an antifungal capacity. The nanobiohybrids (green route) gave an inhibition of fungal growth of ~72.4% while with the ZnO-NPs (chemical route), inhibition was ~87.1%. Microstructural studies using High Resolution Optical Microscopy (HROM) and ultra-structural analysis using TEM carried out on the treated strains demonstrated the effect of the nanofungicides on the vegetative and reproductive structures, as well as on their cell wall. To account for the antifungal effect presented by ZnO-NPs and ZnO nanobiohybrids on the fungi tested, effects reported in the literature related to the action of nanomaterials on biological entities were considered. Specifically, we discuss the electrical interaction of the ZnO-NPs with the cell membrane and the biomolecules (proteins) present in the fungi, taking into account the n-type nature of the ZnO semiconductor and the electrical behavior of the fungal cell membrane and that of the proteins that make up the protein crown.

• Clean Technology
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• v.28 no.2
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• pp.147-154
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• 2022

Titanate nanotubes (TNTs) were synthesized via alkaline hydrothermal treatment using commercial TiO₂ nanoparticles (P25). The TNTs were prepared at various TiO₂/NaOH ratios, hydrothermal temperatures, and hydrothermal times. The synthesized catalysts were characterized by X-ray diffraction, field-emission scanning electron microscopy, N₂ adsorption-desorption isotherms, field-emission transmission electron microscopy, and ultraviolet-visible spectroscopy. TNTs were generated upon a decrease in the TiO₂/NaOH ratio due to the dissolution of TiO₂ in the alkaline solution and the generation of new Ti-O-Ti bonds to form titanate nanoplates and nanotubes. The hydrothermal treatment temperature and time were important factors for promoting the nucleation and growth of TNTs. The TNT catalyst with the largest surface area (389.32 m² g^-1) was obtained with a TiO₂/NaOH ratio of 0.25, a hydrothermal treatment temperature of 130 ℃, and a hydrothermal treatment time of 36 h. Additionally, we investigated the photocatalytic activity of methyl violet 2B (MV) over the TNT catalysts under UV irradiation and found that the degradation efficiencies of the TNTs were higher than that of P25. Among the TNT catalysts, the TNT catalyst that was hydrothermally synthesized for 36 h (TNT 36 h) exhibited a 96.9% degradation efficiency and a degradation rate constant that was 4.8 times higher than P25 due to its large surface area, which allowed for more contact between the MV molecules and TNT surfaces and facilitated rapid electron transfer. Finally, these results were correlated with the specific surface area.

• Proceedings of the Materials Research Society of Korea Conference
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• 2003.11a
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• pp.20-20
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• 2003

We developed 30 ㎽-AlInGaN based violet laser diodes. The fabrication procedures of the laser diodes are described as follows. Firstly, GaN layers having very low defect density were grown on sapphire substrates by lateral epitaxial overgrowth method. The typical dislocation density was about 1-3$\times$10$^{6}$ /$\textrm{cm}^2$ at the wing region. Secondly, AlInGaN laser structures were grown on LEO-GaN/sapphire substrates by MOCVD. UV activation method, instead of conventional annealing, was conducted to achieve good p-type conduction. Thirdly, ridge stripe laser structures were fabricated. The cavity mirrors were formed by cleaving method. Three pairs of SiO$_2$ and TiO$_2$ layers were deposited on the rear facet for mirror coating. Lastly, laser diode chips were mounted on AlN submount wafers by epi-down bonding method. The lifetime of the laser diodes was over 10,000 hrs at room temperature under automatic power controlled condition. We expect the performance of the LDs to be improved by the optimization of the growth and fabrication process. The detailed characteristics and important issues of the laser diodes will be discussed at the conference.

• Nuclear Engineering and Technology
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• v.55 no.5
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• pp.1519-1526
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• 2023

For the first time Aluminium-BariumeZinc oxide nanocomposite (ZABONC) was synthesized by solution combustion method where calcination was carried out at low temperatures (600℃) to study the electromagnetic (EM) (X/γ) radiation shielding properties. Further for characterization purpose standard techniques like PXRD, SEM, UV-VISIBLE, FTIR were used to find phase purity, functional groups, surface morphology, and to do structural analysis and energy band gap determination. The PXRD pattern shows (hkl) planes corresponding to spinel cubic phase of ZnAl₂O4, cubic Ba(NO₃)₂, α and γ phase of Al₂O₃ which clearly confirms the formation of complex nano composite. From SEM histogram mean size of nano particles was calculated and is in the order of 17 nm. Wood and Tauc's relation direct energy band gap calculation gives energy gap of 2.9 eV. In addition, EM (X/γ) shielding properties were measured and compared with the theoretical ones using standard procedures (NaI (Tl) detector and multi channel analyzer MCA). For energy above 356 keV the measured shielding parameters agree well with the theory, while below this value slight deviation is observed, due to the influence of atomic/crystallite size of the ZABONC. Hence synthesized ZABONC can be used as a shielding material in EM (X/γ) radiation shielding.

• Advances in nano research
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• v.15 no.1
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• pp.35-48
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• 2023

Nanoparticles are known for their outstanding properties such as particle size, surface area, optical and electrical properties. These properties have significantly boasted their applications in various surface phenomena. In this work, calcium oxide nanoparticles were synthesized from periwinkle shells as an approach towards waste management through resource recovery. The sol gel method was used for the synthesis. The nanoparticles were characterized using X-Ray diffractometer (XRD), Fourier Transformed Infra-Red Spectrophotometer (FTIR), Brunauer Emmett Teller (BET), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and ultra violet visible spectrophotometer (UV-visible). While DLS and SEM underestimate the particle diameter, the BET analysis reveals surface area of 138.998 m²/g, pore volume = 0.167 m³/g and pore diameter of 2.47 nm. The nanoparticles were also employed as an adsorbent for the purification of dye (methyl orange) contaminated water. The adsorbent showed excellent removal efficiency (up to 97 %) for the dye through the mechanism of physical adsorption. The adsorption of the dye fitted the Langmuir and Temkin models. Analysis of FTIR spectrum after adsorption complemented with computational chemistry modelling to reveal the imine nitrogen group as the site for the adsorption of the dye unto the nanomaterials. The synthesized nanomaterials have an average particle size of 24 nm, showed a unique XRD peak and is thermally and mechanically stable within the investigated temperature range (30 to 70 ℃).

• Journal of Electrochemical Science and Technology
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• v.13 no.2
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• pp.279-291
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• 2022

In this report the thermochemical conversion of Sm₂O₃ to SmCl₃ using AlCl₃ in LiCl-KCl melt at 773 K is discussed. The final product was a mixture of SmCl₃, Al₂O₃, unreacted Sm₂O₃ and AlCl₃ in the chloride melt. The electrochemical attributes of the mixture was analyzed with cyclic voltammetry (CV) and square wave voltammetry (SWV). The crystallographic phases of the mixture were studied with X-ray diffraction (XRD) technique. The major chemical conversion was optimized by varying the effective parameters, such as concentrations of AlCl₃, duration of reaction and the amount of LiCl-KCl salt. The extent of conversion and qualitative assessment of efficiency of the present protocol were evaluated with fluorescence spectroscopy, UV-Vis spectrophotometry and inductively coupled plasma atomic emission spectroscopy (ICP-AES) studies of the mixture. Thus, a critical assessment of the thermochemical conversion efficiency was accomplished by analysing the amount of SmCl₃ in LiCl-KCl melt. In the process, a conversion efficiency of 95% was achieved by doubling the stoichiometric requirement of AlCl₃ in 50 g of LiCl-KCl salt. The conversion reaction was found to be very fast as the reaction reached equilibrium in 15 min.

• Korean Journal of Materials Research
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• v.33 no.7
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• pp.315-322
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• 2023

In the present work, we address the new route for the green synthesis of manganese dioxide (MnO₂) by an innovative method named the solution plasma process (SPP). The reaction mechanism of both colloidal and nanostructured MnO₂ was investigated. Firstly, colloidal MnO₂ was synthesized by plasma discharging in KMnO₄ aqueous solution without any additives such as reducing agents, acids, or base chemicals. As a function of the discharge time, the purple color solution of MnO₄^- (oxidation state +7) was changed to the brown color of MnO₂ (oxidation state +4) and then light yellow of Mn²⁺ (oxidation state +2). Based on the UV-vis analysis we found the optimal discharging time for the synthesis of stable colloidal MnO₂ and also reaction mechanism was verified by optical emission spectroscopy (OES) analysis. Secondly, MnO₂ nanoparticles were synthesized by SPP with a small amount of reducing sugar. The precipitation of brown color was observed after 8 min of plasma discharge and then completely separated into colorless solution and precipitation. It was confirmed layered type of nanoporous birnessite-MnO₂ by X-ray powder diffraction (XRD), fourier-transform infrared spectroscopy (FT-IR), and electron microscopes. The most important merits of this approach are environmentally friendly process within a short time compared to the conventional method. Moreover, the morphology and the microstructure could be controllable by discharge conditions for the appropriate potential applications, such as secondary batteries, supercapacitors, adsorbents, and catalysts.