• Ceramist
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• v.22 no.4
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• pp.350-356
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• 2019

Recently, transition metal dichalcogenide (TMDC) monolayers have been the subject of research exploring the physical phenomenon generated by low dimensionality and high symmetry. One of the keys to understanding new physical observations is the electronic band structure of 2D TMDCs. Angle-resolved photoelectron spectroscopy (ARPES) is, to this point, the best technique for obtaining information on the electronic structure of 2D TMDCs. However, through ARPES research, obtaining the long-range well-ordered single crystal samples always proves a challenging and obstacle presenting issue, which has been limiting towards measuring the electronic band structures of samples. This is particularly true in general 2D TMDCs cases. Here, we introduce the approach, with a mathematical framework, to overcome such ARPES limitations by employing the high level of symmetry of 2D TMDCs. Their high symmetry enables measurement of the clear and sharp electronic band dispersion, which is dominated by the band dispersion of single-crystal TMDCs along the two high symmetry directions Γ-K and Γ-M. In addition, we present two important studies and observations for the direct measuring of the exciton binding energy and charge transfer of 2D TMDCs, both being established by the above novel approach.

• Applied Microscopy
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• v.45 no.3
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• pp.119-125
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• 2015

Two-dimensional (2D) transition metal dichalcogenides (TMDCs) have attracted significant attention due to their unique and exotic properties attributed to their low dimensionality. In particular, semiconducting 2D TMDCs such as $MoS_2$, $WS_2$, $MoSe_2$, and $WSe_2$ have been demonstrated to be feasible for various advanced electronic and optical applications. In these regards, process to synthesize high quality 2D TMDCs layers with high reliability, wafer-scale uniformity, controllable layer number and excellent electronic properties is essential in order to use 2D TMDCs in practical applications. Vapor deposition techniques, such as physical vapor deposition, chemical vapor deposition and atomic layer deposition, could be promising processes to produce high quality 2D TMDCs due to high purity, thickness controllability and thickness uniformity. In this article, we briefly review recent research trend on vapor deposition techniques to synthesize 2D TMDCs.

• 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.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.281.1-281.1
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• 2016

Transition metal dichalcogenides (TMDCs) are promising layered structure materials for next-generation nano electronic devices. Many investigation on the FET device using TMDCs channel material have been performed with some integrated approach. To use TMDCs for channel material of top-gate thin film transistor(TFT), the study on high-k dielectrics on TMDCs is necessary. However, uniform growth of atomic-layer-deposited high-k dielectric film on TMDCs is difficult, owing to the lack of dangling bonds and functional groups on TMDC's basal plane. We demonstrate the effect of remote oxygen plasma pretreatment of large area synthesized few-layer MoSe2 on the growth behavior of Al2O3, which were formed by atomic layer deposition (ALD) using tri-methylaluminum (TMA) metal precursors with water oxidant. We investigated uniformity of Al2O3 by Atomic force microscopy (AFM) and Scanning electron microscopy (SEM). Raman features of MoSe2 with remote plasma pretreatment time were obtained to confirm physical plasma damage. In addition, X-ray photoelectron spectroscopy (XPS) was measured to investigate the reaction between MoSe2 and oxygen atom after the remote O2 plasma pretreatment. Finally, we have uniform Al2O3 thin film on the MoSe2 by remote O2 plasma pretreatment before ALD. This study can provide interfacial engineering process to decrease the leakage current and to improve mobility of top-gate TFT much higher.

• 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.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.375-375
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• 2014

Layered semiconductor materials can be a promising candidate for large-area thin film transistors (TFTs) due to their relatively high mobility, low-power switching, mechanically flexibility, optically transparency, and amenability to a low-cost, large-area growth technique like thermal chemical vapor deposition (CVD). Unlike 2D graphene, series of transition metal dichalcogenides (TMDCs), $MX_2$ (M=Ta, Mo, W, X=S, Se, Te), have a finite bandgap (1~2 eV), which makes them highly attractive for electronics switching devices. Recently, 2D $MoS_2$ materials can be expected as next generation high-mobility thin-film transistors for OLED and LCD backplane. In this paper, we investigate in detail the electrical characteristics of 2D layered $MoS_2$ local bottom-gated transistor with the same device structure of the conventional thin film transistor, and expect the feasibility of display application.

• Journal of the Microelectronics and Packaging Society
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• v.27 no.4
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• pp.119-125
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• 2020

Transition metal dichalcogenides (TMDCs), two-dimensional atomic layered materials with direct bandgap in the range of 1.1-2.1 eV, have attracted a lot of research interest due to their high response to light and capability to build new types of artificial heterostructures. However, the large-area synthesis of high-quality and uniform TMDC films with vertical-stacked heterostructure still remains challenge. In this study, we have developed a metal-organic chemical vapor deposition (MOCVD) system for TMDCs and conducted a systematic study on the growth of single-layer TMDCs and their heterostructures. In particular, using a bubbler-type organometallic compound sources, the concentration and flow rate of each source can be precisely controlled to obtain uniformly single-layered MoS2 and WS2 films over the centimeter scale. In addition, the MoS2/WS2 vertical heterostructure was achieved by growing WS2 film directly on the MoS2 film, as confirmed by electron microscopy, UV-visible spectrophotometer, Raman spectroscopy, and photoluminescence spectroscopy.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.332.2-332.2
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• 2016

Two dimensional transition-metal dichalcogenides (TMDs) semiconductors are attractive materials for optoelectric devices because of their direct energy bandgap and transparency. To investigate the feasibility of transparent p-n junctions, we have fabricated a p-n heterojunction consisting of p-type WSe2 and n-type MoS2 flakes since WSe2 and MoS2 with proper electrode metals exhibit p-type and n-type behaviors, respectively. These heterojunctions exhibits gate-tunable rectifying behaviors and photovoltaic effects (ECE ~ 0.2%) indicating that p-n junctions were formed. In addition, photocurrent and photovoltaic effects were observed under light illumination, which were dependent on the gate voltage. In addition, the photocurrent mapping images indicate that the photovoltaic effects comes from the junction area. Possible origins of gate-tunability are discussed.

• Journal of Oral Medicine and Pain
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• v.48 no.3
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• pp.87-95
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• 2023

Purpose: To quantify the relationship between perceived pain intensity and psychological variables in a sample of participants with temporomandibular disorder, with or without central sensitization (CS). Methods: A cross-sectional study with nonprobability convenience sampling was conducted from January 1, 2022, to June 30, 2023. Pain intensity (Numeric Pain Rating Scale), anxiety (State-Trait Anxiety Questionnaire, STAI), catastrophizing (Pain Catastrophizing Scale, PCS), perceived stress (Perceived Stress Scale, PSS), and sleep quality (Pittsburgh Sleep Quality Index, PSQI) were assessed. Statistical analysis was performed using IBM SPSS Statistics for Windows, Version 20.0 (IBM Co.), which included descriptive and normality analyses and the calculation of strength of multiple correlational regression. Results: A total of 52 (n=34 female 65.4%; n=18 male 34.6%) subjects with diagnosis of temporomandibular disorders (TMD) were finally included. A total of 26 participants (n=26, 50.0%) were cases suffered from CS (TMD-CS mean=46.62±11.24) while the remaining participants (n=26, 50.0%) were the controls (TMD-nCS mean=26.77, standard deviation [SD]=8.42). The pain intensity was moderate in both groups TMDCS (mean=7.62, SD=0.83) and TMD-nCS (mean=7.05, SD=0.86), anxiety (TMD-CS STAI mean=53.27, SD=11.54; TMD-nCS STAI mean=49, SD=11.55), catastrophizing (TMD-CS PCS mean=46.27, SD=9.75; TMD-nCS PCS mean=26.69, SD=4.97), perceived stress (TMDCS PSS mean=30.35, SD=4.91; TMD-nCS PSS mean=26.12, SD=6.60) and sleep quality (TMD-CS PSQI mean=15.81, SD=3.65; TMD-nCS PSQI mean=12.77, SD=2.76) levels were measured in both groups. In TMD-CS and TMD-nCS, higher anxiety levels were moderately and significantly associated with greater pain intensity β=0.4467 (t=2.477, p=0.021) and β=0.5087 (t=2.672, p=0.014). Nevertheless, catastrophizing, perceived stress and sleep quality were not associated to pain intensity in neither of group. Conclusions: In both TMD-CS and TMD-nCS patients, elevated anxiety levels were moderately and significantly associated with increased pain intensity. However, heightened levels of pain catastrophizing, perceived stress, and poor sleep quality were not significantly associated with increased pain intensity in either of the two analyzed groups.