Ultraclean Interface of Metal Chalcogenides with Metal through Confined Interfacial Chalcogenization.

Acquisition of defect-free transition metal dichalcogenides (TMDs) channels with clean heterojunctions is a critical issue in the production of TMD-based functional electronic devices. Conventional approaches have transferred TMD onto a target substrate, and then apply the typical device fabrication processes. Unfortunately, those processes cause physical and chemical defects in the TMD channels. Here, a novel synthetic process of TMD thin films, named confined interfacial chalcogenization (CIC) is proposed. In the proposed synthesis, a uniform TMDlayer is created at the Au/transition metal (TM) interface by diffusion of chalcogen through the upper Au layer and the reaction of chalcogen with the underlying TM. CIC allows for ultraclean heterojunctions with the metals, synthesis of various homo- and hetero-structured TMDs, and in situ TMD channel formation in the last stage of device fabrication. The mechanism of TMD growth is revealed by the TM-accelerated chalcogen diffusion, epitaxial growth of TMD on Au(111). We demonstrated a wafer-scale TMD-based vertical memristors which exhibit excellent statistical concordance in device performance enabled by the ultraclean heterojunctions and superior uniformity in thickness. CIC proposed in this study represents a breakthrough in in TMD-based electronic device fabrication and marking a substantial step toward practical next-generation integrated electronics.

Saliency as Pseudo-Pixel Supervision for Weakly and Semi-Supervised Semantic Segmentation.

Existing studies on semantic segmentation using image-level weak supervision have several limitations, including sparse object coverage, inaccurate object boundaries, and co-occurring pixels from non-target objects. To overcome these challenges, we propose a novel framework, an improved version of Explicit Pseudo-pixel Supervision (EPS++), which learns from pixel-level feedback by combining two types of weak supervision. Specifically, the image-level label provides the object identity via the localization map, and the saliency map from an off-the-shelf saliency detection model offers rich object boundaries. We devise a joint training strategy to fully utilize the complementary relationship between disparate information. Notably, we suggest an Inconsistent Region Drop (IRD) strategy, which effectively handles errors in saliency maps using fewer hyper-parameters than EPS. Our method can obtain accurate object boundaries and discard co-occurring pixels, significantly improving the quality of pseudo-masks. Experimental results show that EPS++ effectively resolves the key challenges of semantic segmentation using weak supervision, resulting in new state-of-the-art performances on three benchmark datasets in a weakly supervised semantic segmentation setting. Furthermore, we show that the proposed method can be extended to solve the semi-supervised semantic segmentation problem using image-level weak supervision. Surprisingly, the proposed model also achieves new state-of-the-art performances on two popular benchmark datasets.

Development of a preliminary environmental risk assessment system by using text mining for introducing alien crops.

Changes in worldwide crop trends and climate change has increased the introduction of alien crops. However, there are always potential side effect issues related to introduced crops, such as the introduced crop becoming a nuisance at the new country or bringing insect pests or microorganisms with the introduced crops. In this study, we developed a crop introduction risk assessment system using text mining method to prevent this problem. First, we designed the "Preliminary Environmental Impact Assessment Index for Alien Crops" based on ecological researches to assess the risks of introduced crops to the natural environment. The questionaries evaluate the target alien crop with previous cases reporting the target crops' adverse effects on the environment, the potential of target crops' direct or indirect damage on the environment. The index has sixteen questions with allocated scores that are divided into 4 categories. The detailed rationales of the questionaries and the assessment index are discussed in main text. Second, we assessed 67 crop species that were introduced or scheduled to be introduced to South Korea with this Preliminary Assessment Index. The literature and data were collected with JabRef, search engines, and from the documents of six international institutions. Finally, based on the preliminary assessment results of selected species, we developed the protocols and a manual for the preliminary environmental risk assessment of introduced species. Final evaluation scores for risk evaluation for introducing crops are suggested (over 70 total score for 'danger' and over 50 points for 'caution required', and under 50 points for 'low expected impact'). Presented crop introduction risk assessment system is effective to identify potential problem making crop species. The protocols and a manual that we provide in this study could be applied to other countries which have similar climate and environmental conditions, or after being adequately modified to their environmental factors such as climate, neighboring countries, major crops according to eating habits, and major vegetation.

High-Throughput Growth of Wafer-Scale Monolayer Transition Metal Dichalcogenide via Vertical Ostwald Ripening.

For practical device applications, monolayer transition metal dichalcogenide (TMD) films must meet key industry needs for batch processing, including the high-throughput, large-scale production of high-quality, spatially uniform materials, and reliable integration into devices. Here, high-throughput growth, completed in 12 min, of 6-inch wafer-scale monolayer MoS2 and WS2 is reported, which is directly compatible with scalable batch processing and device integration. Specifically, a pulsed metal-organic chemical vapor deposition process is developed, where periodic interruption of the precursor supply drives vertical Ostwald ripening, which prevents secondary nucleation despite high precursor concentrations. The as-grown TMD films show excellent spatial homogeneity and well-stitched grain boundaries, enabling facile transfer to various target substrates without degradation. Using these films, batch fabrication of high-performance field-effect transistor (FET) arrays in wafer-scale is demonstrated, and the FETs show remarkable uniformity. The high-throughput production and wafer-scale automatable transfer will facilitate the integration of TMDs into Si-complementary metal-oxide-semiconductor platforms.

An Atomically Thin Optoelectronic Machine Vision Processor.

2D semiconductors, especially transition metal dichalcogenide (TMD) monolayers, are extensively studied for electronic and optoelectronic applications. Beyond intensive studies on single transistors and photodetectors, the recent advent of large-area synthesis of these atomically thin layers has paved the way for 2D integrated circuits, such as digital logic circuits and image sensors, achieving an integration level of ≈100 devices thus far. Here, a decisive advance in 2D integrated circuits is reported, where the device integration scale is increased by tenfold and the functional complexity of 2D electronics is propelled to an unprecedented level. Concretely, an analog optoelectronic processor inspired by biological vision is developed, where 32 × 32 = 1024 MoS2 photosensitive field-effect transistors manifesting persistent photoconductivity (PPC) effects are arranged in a crossbar array. This optoelectronic processor with PPC memory mimics two core functions of human vision: it captures and stores an optical image into electrical data, like the eye and optic nerve chain, and then recognizes this electrical form of the captured image, like the brain, by executing analog in-memory neural net computing. In the highlight demonstration, the MoS2 FET crossbar array optically images 1000 handwritten digits and electrically recognizes these imaged data with 94% accuracy.

Ultralow-dielectric-constant amorphous boron nitride.

Decrease in processing speed due to increased resistance and capacitance delay is a major obstacle for the down-scaling of electronics1-3. Minimizing the dimensions of interconnects (metal wires that connect different electronic components on a chip) is crucial for the miniaturization of devices. Interconnects are isolated from each other by non-conducting (dielectric) layers. So far, research has mostly focused on decreasing the resistance of scaled interconnects because integration of dielectrics using low-temperature deposition processes compatible with complementary metal-oxide-semiconductors is technically challenging. Interconnect isolation materials must have low relative dielectric constants (κ values), serve as diffusion barriers against the migration of metal into semiconductors, and be thermally, chemically and mechanically stable. Specifically, the International Roadmap for Devices and Systems recommends4 the development of dielectrics with κ values of less than 2 by 2028. Existing low-κ materials (such as silicon oxide derivatives, organic compounds and aerogels) have κ values greater than 2 and poor thermo-mechanical properties5. Here we report three-nanometre-thick amorphous boron nitride films with ultralow κ values of 1.78 and 1.16 (close to that of air, κ = 1) at operation frequencies of 100 kilohertz and 1 megahertz, respectively. The films are mechanically and electrically robust, with a breakdown strength of 7.3 megavolts per centimetre, which exceeds requirements. Cross-sectional imaging reveals that amorphous boron nitride prevents the diffusion of cobalt atoms into silicon under very harsh conditions, in contrast to reference barriers. Our results demonstrate that amorphous boron nitride has excellent low-κ dielectric characteristics for high-performance electronics.

Multi-criteria decision support system of the photovoltaic and solar thermal energy systems using the multi-objective optimization algorithm.

When the photovoltaic (PV) and solar thermal energy (STE) systems, which share the rooftop area, are installed in the same building, a trade-off problem occurs in terms of the energy, economic, and environmental aspects, and thus, steps need to solve this problem. Therefore, this study aimed to develop a multi-criteria decision support system of the PV and STE systems using the multi-objective optimization algorithm. This system was developed in the following six steps: (i) database establishment; (ii) designing the variables of the PV and STE systems; (iii) development of the analysis engine of the PV and STE systems; (iv) environmental and economic assessment from the life cycle perspective; (v) integrated multi-objective optimization (iMOO) with a genetic algorithm; and (vi) establishment of a multi-criteria decision support system. To verify the robustness and reliability of the developed model, an analysis of "D" City Hall and "I" Airport as target facilities was performed. The optimal PV and STE systems that consider the energy, economic, and environmental aspects at the same time were determined with respect to the 1.23 × 1015 and 1.05 × 1016 installation scenarios, respectively, in terms of effectiveness. The iMOO scores of the existing PV and STE systems installed in "D" City Hall and "I" Airport were 0.358 and 0.346, respectively, whereas those of the optimal solutions were 0.249 and 0.280, showing score improvements. In terms of efficiency, the times required for determining the optimal solutions were 20 and 30 min, respectively. The developed model makes the final decision-maker to find the optimal solution in introducing the PV and STE systems in the early design phase at the same time.

Vertical MoS2 Double-Layer Memristor with Electrochemical Metallization as an Atomic-Scale Synapse with Switching Thresholds Approaching 100 mV.

Atomically thin two-dimensional (2D) materials-such as transition metal dichalcogenide (TMD) monolayers and hexagonal boron nitride (hBN)-and their van der Waals layered preparations have been actively researched to build electronic devices such as field-effect transistors, junction diodes, tunneling devices, and, more recently, memristors. Two-dimensional material memristors built in lateral form, with horizontal placement of electrodes and the 2D material layers, have provided an intriguing window into the motions of ions along the atomically thin layers. On the other hand, 2D material memristors built in vertical form with top and bottom electrodes sandwiching 2D material layers may provide opportunities to explore the extreme of the memristive performance with the atomic-scale interelectrode distance. In particular, they may help push the switching voltages to a lower limit, which is an important pursuit in memristor research in general, given their roles in neuromorphic computing. In fact, recently Akinwande et al. performed a pioneering work to demonstrate a vertical memristor that sandwiches a single MoS2 monolayer between two inert Au electrodes, but it could neither attain switching voltages below 1 V nor control the switching polarity, obtaining both unipolar and bipolar switching devices. Here, we report a vertical memristor that sandwiches two MoS2 monolayers between an active Cu top electrode and an inert Au bottom electrode. Cu ions diffuse through the MoS2 double layers to form atomic-scale filaments. The atomic-scale thickness, combined with the electrochemical metallization, lowers switching voltages down to 0.1-0.2 V, on par with the state of the art. Furthermore, our memristor achieves consistent bipolar and analogue switching, and thus exhibits the synapse-like learning behavior such as the spike-timing dependent plasticity (STDP), the very first STDP demonstration among all 2D-material-based vertical memristors. The demonstrated STDP with low switching voltages is promising not only for low-power neuromorphic computing, but also from the point of view that the voltage range approaches the biological action potentials, opening up a possibility for direct interfacing with mammalian neuronal networks.

The effects of filters for an intelligent air pollutant control system considering natural ventilation and the occupants.

Experimental analysis was conducted on the indoor air pollutant concentration using natural ventilation and filters. The study targeted two office rooms each of which was occupied by four people, and with the same outdoor environments. A non-woven fabric filter (room A) and an electrostatic filter (room B) were installed on the window frame, and the indoor air pollutant concentration and indoor climate factors were monitored based on the number of occupants and the occupants' activities. The results are as follows: (i) when the number of occupants in each room increased from 0.03-0.06 to 1.53-1.63, room A showed a 60% average PM10 concentration increase while room B showed an opposite result (10% average PM10 concentration decrease), meaning the electrostatic filter's lower resistance to flow contributed to better ventilation and also decreased the influence of the occupants on the indoor air pollutant concentration. A low correlation (0.323-0.350) between the CO2 concentration and the occupants in room B also proved these results; (ii) while the average PM10 concentration in room A was 9 µg/m3 higher than that in room B, the average PM2.5 concentration in room A was higher by only 0.2 µg/m3, which showing that much of the generated or resuspended indoor particulate matter was PM10; and (iii) due to the more frequent heat transfer from outdoors to indoors, room B consumed 23% more heating energy. The results of this study are expected to be used as bases for the establishment of an appropriate management strategy that considers the indoor air pollutant concentration caused by the number of occupants and occupants' activities by combining natural ventilation and filters.

Two-Dimensional Materials Inserted at the Metal/Semiconductor Interface: Attractive Candidates for Semiconductor Device Contacts.

Metal-semiconductor junctions are indispensable in semiconductor devices, but they have recently become a major limiting factor precluding device performance improvement. Here, we report the modification of a metal/n-type Si Schottky contact barrier by the introduction of two-dimensional (2D) materials of either graphene or hexagonal boron nitride (h-BN) at the interface. We realized the lowest specific contact resistivities (ρc) of 3.30 nΩ cm2 (lightly doped n-type Si, ∼ 1015/cm3) and 1.47 nΩ cm2 (heavily doped n-type Si, ∼ 1021/cm3) via 2D material insertion are approaching the theoretical limit of 1.3 nΩ cm2. We demonstrated the role of the 2D materials at the interface in achieving a low ρc value by the following mechanisms: (a) 2D materials effectively form dipoles at the metal-2D material (M/2D) interface, thereby reducing the metal work function and changing the pinning point, and (b) the fully metalized M/2D system shifts the pinning point toward the Si conduction band, thus decreasing the Schottky barrier. As a result, the fully metalized M/2D system using atomically thin and well-defined 2D materials shows a significantly reduced ρc. The proposed 2D material insertion technique can be used to obtain extremely low contact resistivities in metal/n-type Si systems and will help to achieve major performance improvements in semiconductor technologies.

Mesostructured HfxAlyO2 Thin Films as Reliable and Robust Gate Dielectrics with Tunable Dielectric Constants for High-Performance Graphene-Based Transistors.

We introduce a reliable and robust gate dielectric material with tunable dielectric constants based on a mesostructured HfxAlyO2 film. The ultrathin mesostructured HfxAlyO2 film is deposited on graphene via a physisorbed-precursor-assisted atomic layer deposition process and consists of an intermediate state with small crystallized parts in an amorphous matrix. Crystal phase engineering using Al dopant is employed to achieve HfO2 phase transitions, which produce the crystallized part of the mesostructured HfxAlyO2 film. The effects of various Al doping concentrations are examined, and an enhanced dielectric constant of ∼25 is obtained. Further, the leakage current is suppressed (∼10(-8) A/cm(2)) and the dielectric breakdown properties are enhanced (breakdown field: ∼7 MV/cm) by the partially remaining amorphous matrix. We believe that this contribution is theoretically and practically relevant because excellent gate dielectric performance is obtained. In addition, an array of top-gated metal-insulator-graphene field-effect transistors is fabricated on a 6 in. wafer, yielding a capacitance equivalent oxide thickness of less than 1 nm (0.78 nm). This low capacitance equivalent oxide thickness has important implications for the incorporation of graphene into high-performance silicon-based nanoelectronics.

Change of QT variability index during general anesthesia.

BACKGROUND: The QT variability index (QTVI)-a non-invasive measure of beat-to-beat QT interval (QTI) fluctuations-is related to myocardial repolarization lability. The QTVI represents the relationship between QTI and the RR interval. Elevated QTVI is associated with an increased risk of malignant ventricular arrhythmias and sudden death. We investigated the influence of general anesthesia and tourniquets on the QTVI. METHODS: We studied fifty patients who received total knee replacement arthroplasty under sevoflurane anesthesia. We measured QTI, corrected QTI (QTc), T-wave peak-to-end interval (TPE), QTVI, and heart rate variability. All variables were calculated at baseline (B), 30 min after general anesthesia (A), 30 min (TQ1) and 60 min (TQ2) after tourniquet inflation, and at tourniquet deflation (TQR). RESULTS: Prolongation of QTI was detected at all times, and QTc was significantly prolonged TQR. TPE was unchanged during general anesthesia. The QTVI was significantly decreased and more negative during anesthesia and tourniquet inflation. After deflation of the tourniquet, the QTVI was restored to preanesthetic values. Low frequency (LF) was significantly decreased during general anesthesia, but high frequency (HF) was somewhat maintained, except at TQ2. The LF/HF ratio was significantly decreased at A and TQ2. CONCLUSIONS: Sevoflurane based general anesthesia induced repolarization stability and, more negativity of the QTVI, in patients undergoing total knee replacement arthroplasty.

Thickness scaling of atomic-layer-deposited HfO2 films and their application to wafer-scale graphene tunnelling transistors.

The downscaling of the capacitance equivalent oxide thickness (CET) of a gate dielectric film with a high dielectric constant, such as atomic layer deposited (ALD) HfO2, is a fundamental challenge in achieving high-performance graphene-based transistors with a low gate leakage current. Here, we assess the application of various surface modification methods on monolayer graphene sheets grown by chemical vapour deposition to obtain a uniform and pinhole-free ALD HfO2 film with a substantially small CET at a wafer scale. The effects of various surface modifications, such as N-methyl-2-pyrrolidone treatment and introduction of sputtered ZnO and e-beam-evaporated Hf seed layers on monolayer graphene, and the subsequent HfO2 film formation under identical ALD process parameters were systematically evaluated. The nucleation layer provided by the Hf seed layer (which transforms to the HfO2 layer during ALD) resulted in the uniform and conformal deposition of the HfO2 film without damaging the graphene, which is suitable for downscaling the CET. After verifying the feasibility of scaling down the HfO2 thickness to achieve a CET of ~1.5 nm from an array of top-gated metal-oxide-graphene field-effect transistors, we fabricated graphene heterojunction tunnelling transistors with a record-low subthreshold swing value of <60 mV/dec on an 8" glass wafer.

Involvement of Protein Kinase C-δ in Vascular Permeability in Acute Lung Injury.

Pulmonary edema is a major cause of mortality due to acute lung injury (ALI). The involvement of protein kinase C-δ (PKC-δ) in ALI has been a controversial topic. Here we investigated PKC-δ function in ALI using PKC-δ knockout (KO) mice and PKC inhibitors. Our results indicated that although the ability to produce proinflammatory mediators in response to LPS injury in PKC-δ KO mice was similar to that of control mice, they showed enhanced recruitment of neutrophils to the lung and more severe pulmonary edema. PKC-δ inhibition promoted barrier dysfunction in an endothelial cell layer in vitro, and administration of a PKC-δ-specific inhibitor significantly increased steady state vascular permeability. A neutrophil transmigration assay indicated that the PKC-δ inhibition increased neutrophil transmigration through an endothelial monolayer. This suggests that PKC-δ inhibition induces structural changes in endothelial cells, allowing extravasation of proteins and neutrophils.

A Mask-Free Passivation Process for Low Noise Nanopore Devices.

Solid-state nanopores have been studied widely for the label-free analysis of single biomolecules. The translocation of charged biomolecules through a solid-state nanopore is driven by the applied voltage across a thin membrane. The ionic current changes in response to the translocation of DNA through the nanopore. Solid-state nanopores have many advantages over biological nanopores, such as α-hemolysin and MspA, but the high DNA translocation velocity and the inherent noise in solid-state nanopores have hindered its applications to more precise measurements, such as DNA sequencing. This paper reports a simple and reproducible way of passivating the surface of a nanopore device using an insulating layer, photodefinable PDMS (P-PDMS), to reduce noise and enhance the accuracy of the electrical measurements. This new approach does not require a separate photo-mask or sophisticated micro-alignment equipment to pattern the insulating layer. The pit structure on the back side of the support chip serves as a mask, enabling mask-free photolithography, and the insulating layer only on top of the free-standing silicon nitride membrane can be irradiated selectively by UV and removed by subsequent development in toluene. The resulting nanopore device with a small free standing silicon nitride membrane surrounded by a thick insulating layer showed improved noise characteristics. The root-mean-square noise of the ionic current was reduced to 3.8 pA from 90.8 pA by the formation of a micron-thick insulating layer. The overall performance of the nanopores with an insulating layer was improved significantly when tested with the double-stranded DNA (λ-DNA).

A low-noise solid-state nanopore platform based on a highly insulating substrate.

A solid-state nanopore platform with a low noise level and sufficient sensitivity to discriminate single-strand DNA (ssDNA) homopolymers of poly-A40 and poly-T40 using ionic current blockade sensing is proposed and demonstrated. The key features of this platform are (a) highly insulating dielectric substrates that are used to mitigate the effect of parasitic capacitance elements, which decrease the ionic current RMS noise level to sub-10 pA and (b) ultra-thin silicon nitride membranes with a physical thickness of 5 nm (an effective thickness of 2.4 nm estimated from the ionic current) are used to maximize the signal-to-noise ratio and the spatial depth resolution. The utilization of an ultra-thin membrane and a nanopore diameter as small as 1.5 nm allow the successful discrimination of 40 nucleotide ssDNA poly-A40 and poly-T40. Overall, we demonstrate that this platform overcomes several critical limitations of solid-state nanopores and opens the door to a wide range of applications in single-molecule-based detection and analysis.

Framework for the mapping of the monthly average daily solar radiation using an advanced case-based reasoning and a geostatistical technique.

For the effective photovoltaic (PV) system, it is necessary to accurately determine the monthly average daily solar radiation (MADSR) and to develop an accurate MADSR map, which can simplify the decision-making process for selecting the suitable location of the PV system installation. Therefore, this study aimed to develop a framework for the mapping of the MADSR using an advanced case-based reasoning (CBR) and a geostatistical technique. The proposed framework consists of the following procedures: (i) the geographic scope for the mapping of the MADSR is set, and the measured MADSR and meteorological data in the geographic scope are collected; (ii) using the collected data, the advanced CBR model is developed; (iii) using the advanced CBR model, the MADSR at unmeasured locations is estimated; and (iv) by applying the measured and estimated MADSR data to the geographic information system, the MADSR map is developed. A practical validation was conducted by applying the proposed framework to South Korea. It was determined that the MADSR map developed through the proposed framework has been improved in terms of accuracy. The developed MADSR map can be used for estimating the MADSR at unmeasured locations and for determining the optimal location for the PV system installation.

Estimation of the monthly average daily solar radiation using geographic information system and advanced case-based reasoning.

The photovoltaic (PV) system is considered an unlimited source of clean energy, whose amount of electricity generation changes according to the monthly average daily solar radiation (MADSR). It is revealed that the MADSR distribution in South Korea has very diverse patterns due to the country's climatic and geographical characteristics. This study aimed to develop a MADSR estimation model for the location without the measured MADSR data, using an advanced case based reasoning (CBR) model, which is a hybrid methodology combining CBR with artificial neural network, multiregression analysis, and genetic algorithm. The average prediction accuracy of the advanced CBR model was very high at 95.69%, and the standard deviation of the prediction accuracy was 3.67%, showing a significant improvement in prediction accuracy and consistency. A case study was conducted to verify the proposed model. The proposed model could be useful for owner or construction manager in charge of determining whether or not to introduce the PV system and where to install it. Also, it would benefit contractors in a competitive bidding process to accurately estimate the electricity generation of the PV system in advance and to conduct an economic and environmental feasibility study from the life cycle perspective.

Single-step formation of a graphene-metal hybrid transparent and electrically conductive film.

We report here a rapid (10 s of heating) graphene growth method that can be carried out on any desired substrate, including an insulator, thus negating the need for the transfer from the metal substrate. This technique is based on metal-induced crystallization of amorphous carbon (a-C) to graphene, and involves an ultra-thin metal layer that is less than 10 nm in thickness. Rapid annealing of a bilayer of a-C and metal deposited on the surface leads to the formation of graphene film, and to subsequent breaking-up of the thin metal layer underneath the film, thus resulting in the formation of a graphene­metal hybrid film which is both transparent and electrically conducting. Based on Raman studies, we have also systematically compared ultra-thin metal-induced crystallization behavior with a case of conventional thick metal. Based on the present investigation, it was observed that the dominant growth mechanism in ultra-thin metal-induced crystallization is nucleation controlled.