Semiconducting ink based on 2D single‐crystal flakes with dangling‐bond‐free surfaces enables the implementation of high‐performance devices on form‐free substrates by cost‐effective and scalable ...printing processes. However, the lack of solution‐processed p‐type 2D semiconducting inks with high mobility is an obstacle to the development of complementary integrated circuits. Here, a versatile strategy of doping with Br2 is reported to enhance the hole mobility by orders of magnitude for p‐type transistors with 2D layered materials. Br2‐doped WSe2 transistors show a field‐effect hole mobility of more than 27 cm2 V−1 s−1, and a high on/off current ratio of ≈107, and exhibits excellent operational stability during the on‐off switching, cycling, and bias stressing testing. Moreover, complementary inverters composed of patterned p‐type WSe2 and n‐type MoS2 layered films are demonstrated with an ultra‐high gain of 1280 under a driving voltage (VDD) of 7 V. This work unveils the high potential of solution‐processed 2D semiconductors with low‐temperature processability for flexible devices and monolithic circuitry.
Solution‐processed high‐performance p‐type WSe2 thin‐film transistor is successfully fabricated by Br2‐doping with a field‐effect hole mobility of more than 27 cm2 V−1 s−1, and a high on/off current ratio of ≈107. The resulting complementary inverters with patterned p‐type WSe2 and n‐type MoS2 layered films reaches an ultra‐high gain of 1280 under a driving voltage (VDD) of 7 V.
Advances in large‐area and high‐quality 2D transition metal dichalcogenides (TMDCs) growth are essential for semiconductor applications. Here, the gas‐phase alkali metal‐assisted metal‐organic ...chemical vapor deposition (GAA‐MOCVD) of 2D TMDCs is reported. It is determined that sodium propionate (SP) is an ideal gas‐phase alkali‐metal additive for nucleation control in the MOCVD of 2D TMDCs. The grain size of MoS2 in the GAA‐MOCVD process is larger than that in the conventional MOCVD process. This method can be applied to the growth of various TMDCs (MoS2, MoSe2, WSe2, and WSe2) and the generation of large‐scale continuous films. Furthermore, the growth behaviors of MoS2 under different SP and oxygen injection time conditions are systematically investigated to determine the effects of SP and oxygen on nucleation control in the GAA‐MOCVD process. It is found that the combination of SP and oxygen increases the grain size and nucleation suppression of MoS2. Thus, the GAA‐MOCVD with a precise and controllable supply of a gas‐phase alkali metal and oxygen allows achievement of optimum growth conditions that maximizes the grain size of MoS2. It is expected that GAA‐MOCVD can provide a way for batch fabrication of large‐scale atomically thin electronic devices based on 2D semiconductors.
The gas‐phase alkali metal‐assisted MOCVD (GAA‐MOCVD) for 2D semiconductors with advanced nucleation control realizes the grain size enhancement and generation of MoS2 continuous films with large‐scale spatial homogeneity. In addition, this method enables the grain size enhancement to be maximized as a result of precise and controllable feeding of gas‐phase precursors.
Van der Waals (vdW) heterostructures have drawn much interest over the last decade owing to their absence of dangling bonds and their intriguing low‐dimensional properties. The emergence of 2D ...materials has enabled the achievement of significant progress in both the discovery of physical phenomena and the realization of superior devices. In this work, the group IV metal chalcogenide 2D‐layered Ge4Se9 is introduced as a new selection of insulating vdW material. 2D‐layered Ge4Se9 is synthesized with a rectangular shape using the metalcorganic chemical vapor deposition system using a liquid germanium precursor at 240 °C. By stacking the Ge4Se9 and MoS2, vdW heterostructure devices are fabricated with a giant memory window of 129 V by sweeping back gate range of ±80 V. The gate‐independent decay time reveals that the large hysteresis is induced by the interfacial charge transfer, which originates from the low band offset. Moreover, repeatable conductance changes are observed over the 2250 pulses with low non‐linearity values of 0.26 and 0.95 for potentiation and depression curves, respectively. The energy consumption of the MoS2/Ge4Se9 device is about 15 fJ for operating energy and the learning accuracy of image classification reaches 88.3%, which further proves the great potential of artificial synapses.
Ge4Se9, a new insulating 2D‐layered material, is synthesized using metal–organic chemical vapor deposition at 240 °C with low‐reactive precursors. The 2D‐layered Ge4Se9 forms a low band offset with MoS2, exhibiting a large memory window with linear gate‐tunability. As an artificial synapse, the MoS2/Ge4Se9 heterostructure exhibits synaptic updates with low non‐linearity of 0.26 and low energy consumption of 15 fJ.
2D MoS2 has gained attention for the post‐silicon material owing to its atomically thin nature and dangling bond‐free surface. The bi‐layer MoS2 is considered a promising material for electronic ...devices due to its better electrical properties than monolayer MoS2. However, the uniform growth of bi‐layer MoS2 is still challenging. Herein, the uniform growth of bi‐layer MoS2 is demonstrated using gas‐phase alkali metal‐assisted metal–organic chemical vapor deposition (GAA‐MOCVD). Thanks to enhanced metal reactant diffusion length in GAA‐MOCVD, the uniform growth of bi‐layer MoS2 film is achieved even at fast nucleation kinetics for a shorter growth time compared to previously reported MOCVD. The bi‐layer MoS2 field‐effect transistors (FETs) show superior electrical properties such as sheet conductance and electron mobility than monolayer MoS2 FETs. The electron mobility of bi‐layer MoS2 FETs with bismuth contacts reaches a maximum of 92.35 cm2 V−1 s−1. Using the partially grown epitaxial bi‐layer (PGEB) MoS2, it is demonstrated that a photodetector showed a near‐infrared photoresponse with a low dark current that is advantageous for both monolayer and bi‐layer applications. The potential expansion of the growth technique to layer‐by‐layer growth can result in boosted performance across a wide spectrum of electronic and optoelectronic devices employing MoS2.
The GAA‐MOCVD is introduced to realize the epitaxial growth of one additional layer on monolayer MoS2, resulting in bi‐layer MoS2 film with spatial homogeneity and high‐quality, which is challenging to achieve in conventional MOCVD techniques using powder alkali metals. The FETs fabricated by bi‐layer MoS2 films exhibit superior electrical properties including sheet conductance, electron mobility, and on/off ratio.
Multi-step traffic forecasting has always been extremely challenging due to constantly changing traffic conditions. Advanced Graph Convolutional Networks (GCNs) are widely used to extract spatial ...information from traffic networks. Existing GCNs for traffic forecasting are usually shallow networks that only aggregate two- or three-order node neighbor information. Because of aggregating deeper neighborhood information, an over-smoothing phenomenon occurs, thus leading to the degradation of model forecast performance. In addition, most existing traffic forecasting graph networks are based on fixed nodes and therefore need more flexibility. Based on the current problem, we propose Dynamic Adaptive Deeper Spatio-Temporal Graph Convolutional Networks (ADSTGCN), a new traffic forecasting model. The model addresses over-smoothing due to network deepening by using dynamic hidden layer connections and adaptively adjusting the hidden layer weights to reduce model degradation. Furthermore, the model can adaptively learn the spatial dependencies in the traffic graph by building the parameter-sharing adaptive matrix, and it can also adaptively adjust the network structure to discover the unknown dynamic changes in the traffic network. We evaluated ADSTGCN using real-world traffic data from the highway and urban road networks, and it shows good performance.
Layered materials that do not form a covalent bond in a vertical direction can be prepared in a few atoms to one atom thickness without dangling bonds. This distinctive characteristic of limiting ...thickness around the sub-nanometer level allowed scientists to explore various physical phenomena in the quantum realm. In addition to the contribution to fundamental science, various applications were proposed. Representatively, they were suggested as a promising material for future electronics. This is because (i) the dangling-bond-free nature inhibits surface scattering, thus carrier mobility can be maintained at sub-nanometer range; (ii) the ultrathin nature allows the short-channel effect to be overcome. In order to establish fundamental discoveries and utilize them in practical applications, appropriate preparation methods are required. On the other hand, adjusting properties to fit the desired application properly is another critical issue. Hence, in this review, we first describe the preparation method of layered materials. Proper growth techniques for target applications and the growth of emerging materials at the beginning stage will be extensively discussed. In addition, we suggest interlayer engineering via intercalation as a method for the development of artificial crystal. Since infinite combinations of the host–intercalant combination are possible, it is expected to expand the material system from the current compound system. Finally, inevitable factors that layered materials must face to be used as electronic applications will be introduced with possible solutions. Emerging electronic devices realized by layered materials are also discussed.
In recent years, the awareness of the seriousness of the damage caused by fugitive dust and the need to manage it have increased. In particular, construction sites comprise 84% of business places ...that have reported fugitive dust generation, and they are required to have inspection and management to prevent the occurrence of fugitive dust at construction sites. However, the number of complaints in the construction industry due to fugitive dust has increased. The reason for this increase is the fact that existing control measures are defined based on emission processes rather than construction work types, which makes it difficult to apply fugitive dust control measures to construction sites. Therefore, this research evaluated the effectiveness of fugitive dust control measures for construction sites in Korea through a Delphi study. This Delphi study was conducted in two rounds with 12 experts in an on-site panel, and the factors that were determined to be effective control measures were convergence, the content validity ratio (CVR), and stability. This study’s results will be utilized to direct the establishment of future guidelines for fugitive dust control measures based on types of construction work.
•Epidemiologic features of the second and third waves of the coronavirus disease 2019 (COVID-19) pandemic in South Korea were compared.•Strengthening of social distancing policies was delayed in the ...third wave compared with the second wave.•The third wave persisted longer than the second wave, and had a higher case fatality rate.•Early public health intervention is important to control the COVID-19 pandemic.
To compare epidemiologic features of the second and third waves of the coronavirus disease 2019 (COVID-19) pandemic in South Korea.
Nationwide COVID-19 data were collected between 6 May and 30 December 2020. The degree of social activity was estimated using an Internet search trend analysis program for leisure-related keywords, including ‘eating-out’, ‘trip’ and ‘get directions’ (transportation). Demographics, transmission chains, case fatality rates, social activity levels and public health responses were compared between the second (13 August–18 September 2020) and third (4 November 2020–present) waves.
In comparison with the second wave, the third wave was characterized by delayed strengthening of social distancing policies (3 vs. 15 days), longer duration (36 vs. >56 days) and a higher case fatality rate (0.91% vs. 1.26%). There were significant differences in transmission chains between the second and third waves (P < 0.01). In comparison with the second wave, the proportion of local clusters (24.8% vs. 45.7%) was lower in the third wave, and personal contact transmission (38.5% vs. 25.9%) and unknown routes of transmission (23.5% vs. 20.8%) were higher in the third wave.
Early and timely interventions with strengthened social distancing policies should be implemented to suppress and control the COVID-19 pandemic effectively.
The advanced patterning process is the basis of integration technology to realize the development of next-generation high-speed, low-power consumption devices. Recently, area-selective atomic layer ...deposition (AS-ALD), which allows the direct deposition of target materials on the desired area using a deposition barrier, has emerged as an alternative patterning process. However, the AS-ALD process remains challenging to use for the improvement of patterning resolution and selectivity. In this study, we report a superlattice-based AS-ALD (SAS-ALD) process using a two-dimensional (2D) MoS
-MoSe
lateral superlattice as a pre-defining template. We achieved a minimum half pitch size of a sub-10 nm scale for the resulting AS-ALD on the 2D superlattice template by controlling the duration time of chemical vapor deposition (CVD) precursors. SAS-ALD introduces a mechanism that enables selectivity through the adsorption and diffusion processes of ALD precursors, distinctly different from conventional AS-ALD method. This technique facilitates selective deposition even on small pattern sizes and is compatible with the use of highly reactive precursors like trimethyl aluminum. Moreover, it allows for the selective deposition of a variety of materials, including Al
O
, HfO
, Ru, Te, and Sb
Se
.
Cyclodextrins (CDs) have beneficial characteristics for drug delivery, including hydrophobic interior surfaces. Nanocarriers with
-CD ligands have been prepared with simple surface modifications as ...drug delivery vehicles. In this study, we synthesized
-CD derivatives on an Ag-embedded silica nanoparticle (NP) (SiO₂@Ag NP) structure to load and release doxorubicin (DOX). Cysteinyl-
-CD and ethylenediamine-
-CD (EDA-
-CD) were immobilized on the surface of SiO₂@Ag NPs, as confirmed by transmission electron microscopy (TEM), ultraviolet-visible (UV-Vis) spectrophotometry, and Fourier transform infrared (FTIR) spectroscopy. DOX was introduced into the
-CD on the SiO₂@Ag NPs and then successfully released. Neither cysteinyl-
-CD and EDA-
-CD showed cytotoxicity, while DOX-loaded cysteinyl-
-CD and EDA-
-CD showed a significant decrease in cell viability in cancer cells. The SiO₂@Ag NPs with
-CD provide a strategy for designing a nanocarrier that can deliver a drug with controlled release from modified chemical types.
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