• Journal of the Korean Ceramic Society
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• v.56 no.1
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• pp.24-36
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• 2019

Recently, considerable progress and many breakthroughs have been achieved in the growth of two-dimensional materials, especially transition metal dichalcogenides (TMDCs), which attract significant attention owing to their unique properties originating from their atomically thin layered structure. Chemical vapor deposition (CVD) has shown great promise to fabricate large-scale and high-quality TMDC films with exceptional electronic and optical properties. However, the scalable growth of high-quality TMDCs by CVD is yet to meet industrial criteria. Therefore, growth mechanisms should be unveiled for a deeper understanding and further improvement of growth methods are required. This review summarizes the recent progress in the growth methods of TMDCs through CVD and other modified approaches to gain insights into the growth of large-scale and high-quality TMDCs.

• Journal of the Korean Physical Society
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• v.73 no.11
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• pp.1735-1743
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• 2018

Excitons are the most prominent features of the optical properties of monolayer transition-metal dichalcogenides(TMDC). In view of optoelectronics it is very important to understand the decay mechanisms of the excitons of these materials. Auger recombination of excitons are regarded as one of the dominant decay processes. In this paper the Auger constant of recombination is computed based on the approach proposed by Kavoulakis and Baym. We obtain both temperature dependent (from type A, A' processes) and temperature independent (from type B, B' processes) contributions, and a numerical estimate of theoretical result yields the value of constant in the order of $10^{-2}cm^2s^{-1}$, being consistent with existing experimental data. This implies that Auger decay processes severely limit the photoluminescence yield of TMDC-based optoelectronic devices.

• Journal of Sensor Science and Technology
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• v.30 no.2
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• pp.71-75
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• 2021

Recently, transition-metal-based hydroxide materials have attracted significant attention in various electrochemical applications owing to their low cost, high stability, and versatility in composition and morphology. Among these applications, transition-metal-based hydroxides have exhibited significant potential in supercapacitors owing to their multiple redox states that can considerably enhance the supercapacitance performance. In this study, nanostructured Ni-Mn double hydroxide is directly grown on a conductive substrate using an electrodeposition method. Ni-Mn double hydroxide exhibits excellent electrochemical charge-storage properties in a 1 M KOH electrolyte, such as a specific capacitance of 1364 Fg-1 at a current density of 1 mAcm-2 and a capacitance retention of 94% over 3000 charge-discharge cycles at a current density of 10 mAcm-2. The present work demonstrates a scalable, time-saving, and cost-effective approach for the preparation of Ni-Mn double hydroxide with potential application in high-charge-storage kinetics, which can also be extended for other transition-metal-based double hydroxides.

• Proceedings of the Korea Association of Crystal Growth Conference
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• 1998.09a
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• pp.71-71
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• 1998

Transition metal ions, such as Sc, V, Cr and Fe, doped rutile crystals were grown by Floating Zone method. Growth conditions for high quality of crystals depending on the concentration of doped ions were investigated. Grown crystals were cut and polished to thin wafers, and then various types of defects such as homogeneities, low angle grain boundaries, scattering centers, and oxygen vacancies were analyzed. The effects of transition metal ions on defect formation are discussed. Results and discussions on absorption and fluorescence spectra and electrical properties of grown crystals were also reported.

• Applied Microscopy
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• v.50
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• pp.27.1-27.6
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• 2020

Transition metal dichalcogenides (TMD), which is composed of a transition metal atom and chalcogen ion atoms, usually form vacancies based on the knock-on threshold of each atom. In particular, when electron beam is irradiated on a monolayer TMD such as MoS₂ and WS₂, S vacancies are formed preferentially, and they are aligned linearly to constitute line defects. And then, a hole is formed at the point where the successively formed line defects collide, and metal clusters are also formed at the edge of the hole. This study reports a process in which the line defects formed in a monolayer WS₂ sheet expends into holes. Here, the process in which the W cluster, which always occurs at the edge of the formed hole, goes through a uniform intermediate phase is explained based on the line defects and the formation behavior of the hole. Further investigation confirms the atomic structure of the intermediate phase using annular dark field scanning transition electron microscopy (ADF-STEM) and image simulation.

• Proceedings of the Korean Magnestics Society Conference
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• 2003.06a
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• pp.17-17
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• 2003

Semiconductors with ferromagnetism at room temperature has been actively searched for in recent years; a prospect of devices using both charge and spin continuously gives impetus to the activities. Transition metal doped oxide materials have been of particular interest. Co substituted ZnO [1] and TiO$_2$ [2] thin films, for example, were reported to show ferromagnetic properties at room temperature. However, various studies do not seem to converge on a definite picture [3,4,5]. The issue is rather fundamental: whether a system shows ferromagnetic properties at all, and in case it does, whether the system possesses a close coupling between magnetism and transport properties. In this talk, we shall assess the current status of transition metal doped oxide materials as room temperature ferromagnetic semiconductors.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 1998.05a
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• pp.3-3
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• 1998

The atmospheric corrosIOn properties of Zinc (Zn) under wet/dry transition of $H_20$ film were investigated in this study. The atmospheric corrosion of metal is usually occurred as a result of repetitious thickness transition (so called wet/dry transition) of liquid phase which is covering the metal surface. Corrosion potential and the polarization behaviour of Zn during liquid film thickness transition were measured by Kelvin probe method which IS using vibrating reference electrode without touching the liquid film. The oxidized states of Zn as a result of successive wet/dry transition were also investigated by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The results show that the corrosion potential and the corrosIOn rate of Zn both are increasing during drying. However, the corrOSIon rate is decreasing again when the Zn surface is completely dried while the corrosion potential still remains high. This behaviour can be explained by the polarization behaviour change of Zn according to the $H_20$ film thickness change. The completely dried surface is consisted mostly with Zn and ZnO phases. After a number of cycles of wet/dry transition, however, the oxidized Zn phase of ${\varepsilon}-Zn(OH)_2$, which has rather voluminous and defected structure, were found.

• Bulletin of the Korean Chemical Society
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• v.15 no.6
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• pp.436-442
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• 1994

Heterobimetallic complexes have a donor-accepter metal-metal bond in which two electrons from the electron-rich metal moiety are donated to the other electron-deficient one. Based on the competition reactions, Cotton-Kraihanzel force constants, ν(CO)IR band resolution and the relative nucleophilicity comparison of the donor ligands, the following relative ligating ability of the donor ligands toward $M(CO)_5$ (M=Cr, W) is assessed: cis-HW$(CO)_4P(OMe)_3^-$, $HW(CO)_5^-$ > $HCr(CO)_5^-$-$Br^-$ > trans-HFe$(CO)_3P(OMe)_3^-$ > $Mn(CO)_5^-$ > $HFe(CO)_4^-$ > PP$h_3$

• Advances in nano research
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• v.2 no.2
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• pp.77-88
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• 2014

Solvothermal treatment of late transition metal acetylacetonates in a novel medium composed either of pure acetophenone or acetophenone mixtures with amino alcohols offers a general approach to uniform hydrophilic metal nanoparticles with high crystallinity and low degree of aggregation. Both pure metal and mixed-metal particles can be accesses by this approach. The produced materials have been characterized by SEM-EDS, TEM, FTIR in the solid state and by Nanoparticle Tracking Analysis in solutions. The chemical mechanisms of the reactions producing nanoparticles has been followed by NMR. Carrying out the process in pure acetophenone produces palladium metal, copper metal with minor impurity of $Cu_2O$, and NiO. The synthesis starting from the mixtures of Pd and Ni acetylacetonates with up to 20 mol% of Pd, renders in minor yield the palladium-based metal alloy along with nickel oxide as the major phase. Even the synthesis starting from a mixed solution of $Cu(acac)_2$ and $Ni(acac)_2$ produces oxides as major products. The situation is improved when aminoalcohols such as 2-aminoethanol or 2-dimethylamino propanol are added to the synthesis medium. The particles in this case contain metallic elements and pairs of individual metals (not metal alloys) when produced from mixed precursor solutions in this case.

• Particle and aerosol research
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• v.6 no.1
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• pp.29-35
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• 2010

Transition metals such as V, Fe, and Ni were used to synthesize doped zinc oxide nanoparticles from mixed liquid precursors by using the flame spray pyrolysis (FSP). The effects of dopants on the powder properties such as morphology, specific surface area, crystal structure, and light adsorption were analyzed by TEM, BET, XRD, and UV-Vis diffuse reflection spectrum (DRS), respectively. The results showed that hexagonal wurtzite structured ZnO:M (M = V, Fe, Ni) nanoparticles were successfully synthesized by the FSP. The transition metal-doping resulted in the decrease in its particle size and crystallite size. The UV-vis absorption spectra of ZnO:M nanoparticles were also red-shifted. ZnO:V showed the highest MB degradation of 99.4% under the UV irradiation after 3 hrs.