• Korean Journal of Materials Research
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• v.21 no.12
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• pp.639-643
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• 2011

Zinc oxide as an optoelectronic device material was studied to utilize its wide band gap of 3.37 eV and high exciton biding energy of 60 meV. Using anti-site nitrogen to generate p-type zinc oxide has shown a deep acceptor level and low solubility. To increase the nitrogen solubility in zinc oxide, group 13 elements (aluminum, gallium, and indium) was co-added to nitrogen. The effect of aluminum on nitrogen solubility in a $3{\times}3{\times}2$ zinc oxide super cell containing 72 atoms was investigated using density functional theory with hybrid functionals of Heyd, Scuseria, and Ernzerhof (HSE). Aluminum and nitrogen were substituted for zinc and oxygen sites in the super cell, respectively. The band gap of the undoped super cell was calculated to be 3.36 eV from the density of states, and was in good agreement with the experimentally obtained value. Formation energies of a nitrogen molecule and nitric oxide in the zinc oxide super cell in zinc-rich conditions were lower than those in oxygen-rich conditions. When the number of nitrogen molecules near the aluminum increased from one to four in the super cell, their formation energies decreased to approach the valence band maximum to some degree. However, the acceptor level of nitrogen in zinc oxide with the co-incorporation of aluminum was still deep.

• Korean Chemical Engineering Research
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• v.57 no.3
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• pp.408-412
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• 2019

In this study, nitrogen doped carbon felt was prepared by pyrolysis of urea at high temperature and applied as an electrode for vanadium redox flow cell. Urea is easier to handle than ammonia and forms $NH_2$ radicals at higher temperatures, creating a nitrogen functional group on the carbon surface and acting as an active site in the vanadium redox reaction. Therefore, the discharge capacity of activated carbon felt electrodes using urea was 14.9 Ah/L at a current density of $150mA/cm^2$, which is 23% and 187% higher than OGF and GF, respectively. These results show the possibility that activated carbon felt electrode using urea can be used as electrode material for redox flow battery.

• Korean Journal of Materials Research
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• v.31 no.8
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• pp.458-464
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• 2021

Tungsten disulfide (WS₂), a typical 2D layerd structure, has received much attention as a pseudocapacitive material because of its high theoretical specific capacity and excellent ion diffusion kinetics. However, WS₂ has critical limits such as poor long-term cycling stability owing to its large volume expansion during cycling and low electrical conductivity. Therefore, to increase the high-rate performance and cycling stability for pseudocapacitors, well-dispersed WS₂ nanoparticles embedded in carbon nanofibers (WS₂-CNFs), including mesopores and S-doping, are prepared by hydrothermal synthesis and sulfurizaiton. These unique nanocomposite electrodes exhibit a high specific capacity (159.6 F g^-1 at 10 mV s^-1), excellent high-rate performance (81.3 F g^-1 at 300 mV s^-1), and long-term cycling stability (55.9 % after 1,000 cycles at 100 mV s^-1). The increased specific capacity is attributed to well-dispersed WS₂ nanoparticles embedded in CNFs that the enlarge active area; the increased high-rate performance is contributed by reduced ion diffusion pathway due to mesoporous CNFs and improved electrical conductivity due to S-doped CNFs; the long-term cycling stability is attributed to the CNFs matrix including WS₂ nanoparticles, which effectively prevent large volume expansion.

• Journal of the Semiconductor & Display Technology
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• v.21 no.3
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• pp.101-104
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• 2022

Mist-CVD is known to have advantages of low cost and high productivity compared to ALD and PECVD methods. It is capable of reacting to the substrate by misting an aqueous solution using ultrasonic waves under vacuum-free conditions of atmospheric pressure. In particular, Ga₂O₃ is regarded as advanced power semiconductor material because of its high quality of transmittance, and excellent electrical conductivity through N-type doping. In this study, Computational Fluid Dynamics were used to predict the uniformity of the thin film on a large-area substrate. And also the deposition pattern and uniformity were analyzed using the flow velocity and particle tracking method. The uniformity was confirmed by quantifying the deposition cross section with an FIB-SEM, and the consistency of the uniformity prediction was secured through the analysis of the CFD distribution. With the analysis and experimental results, the match rate of deposition area was 80.14% and the match rate of deposition thickness was 55.32%. As the experimental and analysis results were consistent, it was confirmed that it is possible to predict the deposition thickness uniformity of Mist-CVD.

• Journal of Powder Materials
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• v.29 no.5
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• pp.424-431
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• 2022

3Y-TZP ceramics obtained by doping 3 mol.% of Y₂O₃ to ZrO₂ to stabilize the phase transition are widely used in the engineering ceramic industry due to their excellent mechanical properties such as high strength, fracture toughness, and wear resistance. An additional increase in mechanical properties is possible by manufacturing a composite in which a high-hardness material such as oxide or carbide is added to the 3Y-TZP matrix. In this study, composite powder was prepared by dispersing a designated percentage of WC in the 3Y-TZP matrix, and the results were compared after manufacturing the composite using the different processes of spark plasma sintering and HP. The difference between the densification behavior and porosity with the process mechanism was investigated. The correlation between the process conditions and phase formation was examined based on the crystalline phase formation behavior. Changes to the microstructure according to the process conditions were compared using field-emission scanning electron microscopy. The toughness-strengthening mechanism of the composite with densification and phase formation was also investigated.

• Journal of Powder Materials
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• v.29 no.6
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• pp.468-476
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• 2022

Yttria-stabilized zirconia (YSZ) has a low thermal conductivity, high thermal expansion coefficient, and excellent mechanical properties; thus, it is used as a thermal barrier coating material for gas turbines. However, during long-time exposure of YSZ to temperatures of 1200℃ or higher, a phase transformation accompanied by a volume change occurs, causing the YSZ coating layer to peel off. To solve this problem, YSZ has been doped with trivalent and tetravalent oxides to obtain coating materials with low thermal conductivity and suppressed phase transformation of zirconia. In this study, YSZ is doped with trivalent oxides, Nd₂O₃, Yb₂O₃, Al₂O₃, and tetravalent oxide, TiO₂, and the thermal conductivity of the obtained materials is analyzed according to the composition; furthermore, the relative density change, microstructure change, and m-phase formation behavior are analyzed during long-time heat treatment at high temperatures.

• Advances in nano research
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• v.14 no.6
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• pp.507-519
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• 2023

Postsurgical infections are caused by implant-related pathogenic microorganisms that lead to graft rejection. Hence, an intrinsically antibacterial material is required to produce a biocompatible biomaterial with osteogenic properties that could address this major issue. Hence, this current research aims to make strontium-doped hydroxyapatite nanorods (SrHANRs) via an ethylene diamine tetraacetic acid (EDTA)-enable microwave mediated method using Anodontia alba seashells for biomedical applications. This investigation also perceives that EDTA acts as a soft template to accomplish Sr-doping and mesoporous structures in pure hydroxyapatite nanorods (HANRs). The X-ray diffraction (XRD) and transmission electron microscopy (TEM) analysis reveals the crystalline and mesoporous structures, and Brunauer-Emmett-Teller (BET) indicates the surface area of all the samples, including pure HANRs and doped HANRs. In addition, the biocidal ability was tested using various implant-related infectious bacteria pathogens, and it was discovered that Sr-doped HANRs have excellent biocidal properties. Furthermore, toxicity evaluation using zebrafish reports the non-toxic nature of the produced HANRs. Incorporating Sr²⁺ ions into the HAp lattice would enhance biocompatibility, biocidal activity, and osteoconductive properties. As a result, the biocompatible HANRs materials synthesized with Sr-dopants may be effective in bone regeneration and antibacterial in-built implant applications.

• Korean Journal of Materials Research
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• v.33 no.11
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• pp.491-496
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• 2023

As the demand for p-type semiconductors increases, much effort is being put into developing new p-type materials. This demand has led to the development of novel new p-type semiconductors that go beyond existing p-type semiconductors. Copper iodide (CuI) has recently received much attention due to its wide band gap, excellent optical and electrical properties, and low temperature synthesis. However, there are limits to its use as a semiconductor material for thin film transistor devices due to the uncontrolled generation of copper vacancies and excessive hole doping. In this work, p-type CuI semiconductors were fabricated using the chemical vapor deposition (CVD) process for thin-film transistor (TFT) applications. The vacuum process has advantages over conventional solution processes, including conformal coating, large area uniformity, easy thickness control and so on. CuI thin films were fabricated at various deposition temperatures from 150 to 250 ℃ The surface roughness root mean square (RMS) value, which is related to carrier transport, decreases with increasing deposition temperature. Hall effect measurements showed that all fabricated CuI films had p-type behavior and that the Hall mobility decreased with increasing deposition temperature. The CuI TFTs showed no clear on/off because of the high concentration of carriers. By adopting a Zn capping layer, carrier concentrations decreased, leading to clear on and off behavior. Finally, stability tests of the PBS and NBS showed a threshold voltage shift within ±1 V.

• Journal of the Microelectronics and Packaging Society
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• v.30 no.4
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• pp.32-43
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• 2023

Resistive Random Access Memory (RRAM), based on resistive switching characteristics, is emerging as a next-generation memory device capable of efficiently processing large amounts of data through its fast operation speed, simple device structure, and high-density implementation. Interface type resistive switching offer the advantage of low operation currents without the need for a forming process. Especially, for RRAM devices based on transition metal oxides, various studies are underway to enhance the memory characteristics, including precise material composition control and improving the reliability and stability of the device. In this paper, we introduce various methods, such as doping of heterogeneous elements, formation of multilayer films, chemical composition adjustment, and surface treatment to prevent degradation of interface type resistive switching properties and enhance the device characteristics. Through these approaches, we propose the feasibility of implementing high-efficient next-generation non-volatile memory devices based on improved resistive switching properties.

• Clean Technology
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• v.30 no.1
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• pp.23-27
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• 2024

Bismuth is a promising anodic for Li-ion batteries (LIBs) due to its adequate operating voltage and high-volume capacity (3,765 mAh cm^-3). Nevertheless, inevitable volume expansion during Bi alloy reactions leads to severe capacity loss and cell destruction. To address this, a complex of bismuth alloy nanoparticles (Bi@NC) embedded in an N doping-carbon coating is fabricated via a simple pyrolysis method. Nano-sized bismuth alloys can improve the reaction dynamics through a shortened Li⁺-ion diffusion path. In addition, the N-doped carbon coating effectively buffers the volume change of bismuth during the extended alloy/dealloy reaction with Li⁺ ions and maintains an effective conductive network. Based on the Thermogravimetric analysis (TGA) showed high bismuth alloy loading (80.9 wt%) and maintained a high gravimetric capacity of 315 mAh g^-1 up to 100 cycles with high volumetric capacity of 845.6 mAh cm^-3.