• Journal of Industrial and Engineering Chemistry
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• v.67
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• pp.28-51
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• 2018

Graphitic carbon nitride ($g-C_3N_4$) as a fascinating visible light active semiconductor photocatalyst has medium band gap, non-toxic nature, stable chemical structure and high thermal stability. Recently, intensive researches are focused on photocatalytic activity of $g-C_3N_4$ for wastewater treatment. This review demonstrates latest progress in fabrication of graphitic carbon nitride $C_3N_4$ incorporated nanocomposite to explore photocatalytic ability for water purification. The $g-C_3N_4$-based nanocomposites were categorized as $g-C_3N_4$ metal-free nanocomposite, noble metals/$g-C_3N_4$ heterojunction, non-metal doped $g-C_3N_4$, transition and post transition metal based $g-C_3N_4$ nanocomposite. Apart from fabrication methods, we emphasized on elaborating the mechanism of activity enhancement during photocatalytic process.

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.63.1-63.1
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• 2015

The next generation electronics need to not only be smaller but also be more flexible. To meet such demands, van der Waals (vdW) heterostructures using two dimensional (2D) atomic crystals such as graphene, hexagonal boron nitride (h-BN) and transition metal dichalcogenides (TMDCs) have been attracted intensely. In particular, for high performance of vdW heterostructures device, ultraclean interface between stacked 2D atomic crystals should be guaranteed. In this talk, I will present fabrication and characterization of the vdW field effect transistors toward performance enhancement by employing TMDCs channel, h-BN insulating layer and graphene electrode. Furthermore, it will also be introduced the characterization and surface engineering of graphene for gas molecule sensor.

• Journal of Powder Materials
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• v.28 no.2
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• pp.150-163
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• 2021

Interest in eco-friendly materials with high efficiencies is increasing significantly as science and technology undergo a paradigm shift toward environment-friendly and sustainable development. MXenes, a class of two-dimensional inorganic compounds, are generally defined as transition metal carbides or nitrides composed of few-atoms-thick layers with functional groups. Recently MXenes, because of their desirable electrical, thermal, and mechanical properties that emerge from conductive layered structures with tunable surface terminations, have garnered significant attention as promising candidates for energy storage applications (e.g., supercapacitors and electrode materials for Li-ion batteries), water purification, and gas sensors. In this review, we introduce MXenes and describe their properties and research trends by classifying them into two main categories: transition metal carbides and nitrides, including Ti-based MXenes, Mo-based MXenes, and Nb-based MXenes.

• Vacuum Magazine
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• v.5 no.2
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• pp.18-22
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• 2018

wo dimensional (2D) van der Waals (vdW) nanosheet semiconductors have recently attracted much attention from researchers because of their potentials as active device materials toward future nano-electronics and -optoelectronics. This review mainly focuses on the features and applications of state-of-the-art vdW 2D material devices which use transition metal dichalcogenides, graphene, hexagonal boron nitride (h-BN), and black phosphorous: field effect transistors (FETs), complementary metal oxide semiconductor (CMOS) inverters, Schottky diode, and PN diode. In a closing remark, important remaining issues of 2D vdW devices are also introduced as requests for future electronics and photonics applications.

• 한국신재생에너지학회:학술대회논문집
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• 2009.06a
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• pp.781-781
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• 2009

We demonstrate that trasition metal catalyst nanoparticle (NP) attached to carbon nitride nanotubes (CNNTs) show selective catalytic activities on hydrogen generation from the water solution including chemical hydride negative ions. The natural bonding orbitals (NBO) obtained from the first-principle calculations shows that the catalysts attached on CNNTs are quite differently polarized when they play for hydrogen generation from chemical hydride ions and hydrogen of water. For Co and Ni nanoparticles attached on CNNTs, their charges are more positively polarized when they interact with $BH_4^-Na^+$ and $H_2O$ while Pt atoms are less positively charged. In this matter, the increased positive charges on catlyst nanoparticles are proven to be more efficient in attracting hydride negative ions, thus improving hydrogen generate rates. Consequently, this result implies that these different charge polarization leads to selective catalytic activities of NPs-CNNTs. In the hydrogen generation experiments, Co-CNNTs shows the highest hydrogen generation rate when the similar amounts of catalyst nanoparticles (Co, Ni, and Pt) are dispersed on the sidewalls of CNNTs.

• Journal of Powder Materials
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• v.31 no.1
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• pp.57-76
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• 2024

Recent advancements in electronic devices and wireless communication technologies, particularly the rise of 5G, have raised concerns about the escalating electromagnetic pollution and its potential adverse impacts on human health and electronics. As a result, the demand for effective electromagnetic interference (EMI) shielding materials has grown significantly. Traditional materials face limitations in providing optimal solutions owing to inadequacy and low performance due to small thickness. MXene-based composite materials have emerged as promising candidates in this context owing to their exceptional electrical properties, high conductivity, and superior EMI shielding efficiency across a broad frequency range. This review examines the recent developments and advantages of MXene-based composite materials in EMI shielding applications, emphasizing their potential to address the challenges posed by electromagnetic pollution and to foster advancements in modern electronics systems and vital technologies.

• Resources Recycling
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• v.31 no.1
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• pp.46-55
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• 2022

The recycling of coated cemented carbide scraps is becoming increasingly significant for the recovery of rare metals. However, coatings consisting of Group IV and V transition metal nitrides are one of the challenging factors in obtaining high-purity materials. We investigated the structural, elastic, and mechanical properties of Group IV and V transition-metal nitrides (TiN, VN, ZrN, NbN, HfN, and TaN) using first-principle calculations. Convergence tests were performed to obtain reliable calculated results. The equilibrium structures of the nitrides were in good agreement with those of a previous study, indicating the reliability of the data. Group IV transition metal nitrides show a higher covalent bonding nature. Thus, they exhibit a higher degree of brittleness than that of Group V transition metal nitrides. In contrast, Group V transition metal nitrides show weaker resistance to shear loading and more ductile behavior than Group IV transition metal nitrides because of the metallic bonds characterized by valence electron concentration. The results of the crystal orbital Hamilton population analysis showed good agreement with the shear resistance tendencies of all transition metal nitrides.

• Progress in Superconductivity and Cryogenics
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• v.20 no.4
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• pp.20-25
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• 2018

Niobium nitride (NbN) superconducting thin films with the thickness of 100 and 400 nm have been deposited on the surfaces of silicon oxide/silicon substrates using a sputtering method. Their superconducting properties have been evaluated in terms of the transition temperature, critical magnetic field, and critical current density. In addition, the NbN films were patterned in a line with a width of $10{\mu}m$ by a reactive ion etching (RIE) process for their characterization. This study proves the applicability of the standard complementary metal-oxide-semiconductor (CMOS) process in the fabrication of superconducting thin films without considerable degradation of superconducting properties.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.270-270
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• 2011

전이금속(transition metal) 질화물(nitride)은 높은 경도, 내마모성, 부식 저항성 그리고 내열성 등과 같은 우수한 기계적 물성 때문에 많은 연구가 되어 왔다. 이 중 질화 티타늄은 높은 경도, 내식 및 내마모의 우수한 기계적 특성으로 공구(tool)와 같은 제품의 수명 향상을 위한 표면 코팅소재로 사용되어 왔으며, 금(gold)색의 미려한 색상을 이용한 제품의 외관 표면처리와 인체에 무해한 특성을 활용한 정형외과 및 치과용 보형물의 수명 및 안정성 향상 등 다양한 분야에 응용 되고 있다. 본 연구에서는 아크방전을 이용한 경사 코팅법으로 질화 티타늄을 합성하였으며, 경사 코팅에 따른 단층 및 다층 박막(2~3 layer)의 미세조직 변화와 그 물성을 평가하였다. 아크 소스에 장착된 타겟은 120 $mm{\Phi}$, 99.5%의 Ti 타겟을 사용하였고, 시편과 타겟 간의 거리는 약 30 cm이며, 시편은 냉연강판과 SUS를 사용하였다. 시편을 진공용기에 장착하고 ~10-6 Torr까지 진공배기를 실시하고, Ar 가스를 진공용기 내로 공급하여 ~10-4 Torr에서 시편에 bias (Pulse : 400 V)를 인가한 후 아크를 발생시켜 약 5분간 청정을 실시하였다. 플라즈마 청정이 끝나면 시편에 인가된 bias를 차단하고 코팅하였다. 경사 코팅을 위한 시편의 회전각은 45$^{\circ}$, -45$^{\circ}$이며, 질화 티타늄의 두께는 약 3 ${\mu}m$로 동일하게 코팅 하였다. 45$^{\circ}$ 단일층의 경우 0$^{\circ}$ 단일층보다 경도가 감소하나 zigzag 구조의 다층으로 갈수록 45$^{\circ}$ 단일층과 비교하여 확연히 경도가 증가함을 볼 수 있었다. 다층 질화 티타늄의 경사 코팅을 통해 박막의 미세조직 변화를 SEM 이미지를 통해 확인하였으며 증착 방식에 따라 경도, 조도, 반사도 등의 물성 변화가 나타났다. 본 연구에서 얻어진 결과를 이용하여 다양한 형태의 박막구조 제어를 통한 물성변화가 가능할 것으로 예상된다.

• Korean Journal of Materials Research
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• v.22 no.5
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• pp.243-248
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• 2012

ZrN nanoparticles were prepared by an exothermic reduction of $ZrCl_4$ with $NaN_3$ in the presence of NaCl flux in a nitrogen atmosphere. Using a solid-state combustion approach, we have demonstrated that the zirconium nitride nanoparticles synthesis process can be completed in only several minutes compared with a few hours for previous synthesis approaches. The chemistry of the combustion process is not complex and is based on a metathesis reaction between $ZrCl_4$ and $NaN_3$. Because of the low melting and boiling points of the raw materials it was possible to synthesize the ZrN phase at low combustion temperatures. It was shown that the combustion temperature and the size of the particles can be readily controlled by tuning the concentration of the NaCl flux. The results show that an increase in the NaCl concentration (from 2 to 13 M) results in a temperature decrease from 1280 to $750^{\circ}C$. ZrN nanoparticles have a high surface area (50-70 $m^2/g$), narrow pore size distribution, and nano-particle size between 10 and 30 nm. The activation energy, which can be extracted from the experimental combustion temperature data, is: E = 20 kcal/mol. The method reported here is self-sustaining, rapid, and can be scaled up for a large scale production of a transition metal nitride nanoparticle system (TiN, TaN, HfN, etc.) with suitable halide salts and alkali metal azide.