Polymer-Waveguide-Integrated 2D Semiconductor Heterostructures for Optical Communications.

The demand for high-speed and low-loss interconnects in modern computer architectures is difficult to satisfy by using traditional Si-based electronics. Although optical interconnects offer a promising solution owing to their high bandwidth, low energy dissipation, and high-speed processing, integrating elements such as a light source, detector, and modulator, comprising different materials with optical waveguides, presents many challenges in an integrated platform. Two-dimensional (2D) van der Waals (vdW) semiconductors have attracted considerable attention in vertically stackable optoelectronics and advanced flexible photonics. In this study, optoelectronic components for exciton-based photonic circuits are demonstrated by integrating lithographically patterned poly(methyl methacrylate) (PMMA) waveguides on 2D vdW devices. The excitonic signals generated from the 2D materials by using laser excitation were transmitted through patterned PMMA waveguides. By introducing an external electric field and combining vdW heterostructures, an excitonic switch, phototransistor, and guided-light photovoltaic device on SiO2/Si substrates were demonstrated.

Proximity-Induced Tunable Magnetic Order at the Interface of All-van der Waals-Layered Heterostructures.

Spin-orbit coupling (SOC) plays a crucial role in controlling the spin-charge conversion efficiency, spin torque, and complex magnetic spin structures. In this study, we investigate the interplay between SOC and ferromagnetism in heterostructures of large-SOC and magnetic materials. We highlight the importance of the SOC-proximity effect on magnetic ordering in all-van der Waals-layered heterostructures, specifically Fe3GeTe2(FGT)/monolayer W1-xVxSe2 (x = 0 and 0.05). By increasing the SOC strength, we demonstrate various magnetic orderings induced at the interface of the heterostructure, including spin-flop, spin-flip, and inverted magnetization. Moreover, we show a sharp magnetic switching from antiferromagnetic state to ferromagnetic state in FGT/W0.95V0.05Se2, which is characteristic of the synthetic antiferromagnetic structure. This proof-of-concept result offers the possibility of interface-tailoring spintronics, including two-dimensional magnetoresistive random access memory toggle switching. Our findings provide insight into the design and development of next-generation spintronic devices by exploiting the interplay between SOC and magnetic ordering in all-van der Waals-layered heterostructures.

Probing Interfacial Charge Transfer between Amyloid-ß and Graphene during Amyloid Fibrillization Using Raman Spectroscopy.

Charge transfer plays a key role in the structural transformation of amyloid-ß proteins (Aßs), as it fibrillizes from small monomers to intermediate oligomers and to ordered fibrils. While the protein fibrillization states have been identified using cryo-electron microscopy, X-ray diffraction, Raman, infrared, terahertz spectroscopies, etc., there is little known about the electronic states during the fibrilization of Aß protein. Here, we probe the charge transfer of Aß42 proteins at different aggregation stages adsorbed on monolayer graphene (Gr) and molybdenum disulfide (MoS2) using Raman spectroscopy. Monomers, oligomers, and fibrils prepared in buffer solutions were deposited and dried separately on Gr and MoS2 where well-established characteristic Raman modes (G, 2D for Gr and E2g, A1g for MoS2) were monitored. The shifts in Raman parameters showed that the small Aß monomers withdraw electrons, whereas fibrils donate electrons to Gr and MoS2. Oligomers undergo transient charge states near the neutrality point. This is explained in terms of modulated carrier concentration in Gr and MoS2. This finding provides insight into the electronic properties of Aßs that could be essential to identifying the onset of toxic fibril forms and developing a straightforward, label-free diagnosis using Gr and MoS2.

Internal Thermal Stress-Driven Phase Transformation in Van der Waals Layered Materials.

High pressure or strain is an effective strategy for generating phase transformations in van der Waals (vdW) layered materials without introducing defects, but this approach remains difficult to perform consistently. We present a scalable and facile method for achieving phase transformation in vdW materials, wherein solid vdW materials are subject to internal thermal stress within a molten metal mantle as it undergoes cooling. This internal thermal stress is principally the product of differential thermal expansion between mantle and core and can be tuned by the mantle material and temperature conditions. We validated this approach by achieving phase transformation of red phosphorus to black phosphorus, and metallic 1T'- to semiconducting 2H-MoTe2 crystals. We further demonstrate quantum electronic phase transformation of suppressed charge density wave in TiSe2 by means of electron-phonon coupling using the same system.

Escalating Ferromagnetic Order via Se-Vacancies Near Vanadium in WSe2 Monolayers.

Magnetic order has been proposed to arise from a variety of defects, including vacancies, antisites, and grain boundaries, which are relevant in numerous electronics and spintronics applications. Nevertheless, its magnetism remains controversial due to the lack of structural analysis. The escalation of ferromagnetism in vanadium-doped WSe2 monolayer is herein demonstrated by tailoring complex configurations of Se vacancies (SeVac ) via post heat-treatment. Structural analysis of atomic defects is systematically performed using transmission electron microscopy (TEM), enabled by the monolayer nature. Temperature-dependent magnetoresistance hysteresis ensures enhanced magnetic order after high-temperature heat-treatment, consistent with magnetic domain analysis from magnetic force microscopy (MFM). The vanadium-Se vacancy pairing is a key to promoting ferromagnetism via spin-flip by electron transfer, predicted from density-functional-theory (DFT) calculations. The approach toward nanodefect engineering paves a way to overcome weak magnetic order in diluted magnetic semiconductors (DMSs) for renovating semiconductor spintronics.

Deep Learning-Assisted Quantification of Atomic Dopants and Defects in 2D Materials.

Atomic dopants and defects play a crucial role in creating new functionalities in 2D transition metal dichalcogenides (2D TMDs). Therefore, atomic-scale identification and their quantification warrant precise engineering that widens their application to many fields, ranging from development of optoelectronic devices to magnetic semiconductors. Scanning transmission electron microscopy with a sub-Å probe has provided a facile way to observe local dopants and defects in 2D TMDs. However, manual data analytics of experimental images is a time-consuming task, and often requires subjective decisions to interpret observed signals. Therefore, an approach is required to automate the detection and classification of dopants and defects. In this study, based on a deep learning algorithm, fully convolutional neural network that shows a superior ability of image segmentation, an efficient and automated method for reliable quantification of dopants and defects in TMDs is proposed with single-atom precision. The approach demonstrates that atomic dopants and defects are precisely mapped with a detection limit of ≈1 × 1012 cm-2 , and with a measurement accuracy of ≈98% for most atomic sites. Furthermore, this methodology is applicable to large volume of image data to extract atomic site-specific information, thus providing insights into the formation mechanisms of various defects under stimuli.

Measuring Photoexcited Free Charge Carriers in Mono- to Few-Layer Transition-Metal Dichalcogenides with Steady-State Microwave Conductivity.

Photoinduced generation of mobile charge carriers is the fundamental process underlying many applications, such as solar energy harvesting, solar fuel production, and efficient photodetectors. Monolayer transition-metal dichalcogenides (TMDCs) are an attractive model system for studying photoinduced carrier generation mechanisms in low-dimensional materials because they possess strong direct band gap absorption, large exciton binding energies, and are only a few atoms thick. While a number of studies have observed charge generation in neat TMDCs for photoexcitation at, above, or even below the optical band gap, the role of nonlinear processes (resulting from high photon fluences), defect states, excess charges, and layer interactions remains unclear. In this study, we introduce steady-state microwave conductivity (SSMC) spectroscopy for measuring charge generation action spectra in a model WS2 mono- to few-layer TMDC system at fluences that coincide with the terrestrial solar flux. Despite utilizing photon fluences well below those used in previous pump-probe measurements, the SSMC technique is sensitive enough to easily resolve the photoconductivity spectrum arising in mono- to few-layer WS2. By correlating SSMC with other spectroscopy and microscopy experiments, we find that photoconductivity is observed predominantly for excitation wavelengths resonant with the excitonic transition of the multilayer portions of the sample, the density of which can be controlled by the synthesis conditions. These results highlight the potential of layer engineering as a route toward achieving high yields of photoinduced charge carriers in neat TMDCs, with implications for a broad range of optoelectronic applications.

Prospective comparison of endoscopic bilateral stent-in-stent versus stent-by-stent deployment for inoperable advanced malignant hilar biliary stricture.

BACKGROUND AND AIMS: Although the efficacy of palliative bilateral biliary drainage using self-expandable metal stents has been demonstrated, it is unclear which bilateral method is optimal for advanced malignant hilar biliary strictures (MHSs). This pilot study compared bilateral stent-in-stent (SIS) with stent-by-stent (SBS) deployment for advanced MHSs. METHODS: Patients with inoperable high-grade MHSs were enrolled in this prospective randomized multicenter study. The primary outcome was the rate of adverse events, whereas secondary outcomes were technical and clinical success, reintervention, therapeutic outcomes, stent patency, and survival duration. RESULTS: This study randomized 69 of 74 pathologically diagnosed patients to the SIS (n = 34) or SBS (n = 35) groups. The total adverse event rate after stent deployment did not differ between the 2 groups (23.5% in the SIS group vs 28.6% in the SBS group, P = .633). The primary technical success rate was 100% (34/34) and 91.4% (32/35) in the SIS and SBS groups, respectively (P = .081). The clinical success rate was 94.1% (32/34) and 90.6% (29/32), respectively (P = .668). The stent patency rate at 3 months was 85.3% in the SIS group and 65.7% in the SBS group (P = .059). At 6 months, the stent patency rate was 47.1% and 31.4%, respectively (P = .184). The median cumulative stent patency and survival probability did not differ between the 2 groups. CONCLUSIONS: Efficacy of bilateral SIS and SBS deployment may be similar in terms of total adverse events, technical and clinical success, stent patency, and survival. The stent patency rates at 3 and 6 months was higher in the SIS group without statistical difference. (Clinical trial registration number: NCT01141088.).

Efficacy and safety of daclatasvir plus asunaprevir for Korean patients with HCV genotype Ib infection: a retrospective multi-institutional study.

BACKGROUND/AIMS: The combination of daclatasvir (DCV) and asunaprevir (ASV) has demonstrated a high sustained virologic response at 12 weeks (SVR12) and a low rate of adverse events in previous clinical studies. The purpose of this study was to clarify the results of treatment and side effects in Korean patients with chronic hepatitis C virus (HCV) genotype Ib infection. METHODS: We retrospectively analyzed clinical data from chronic HCV genotype Ib patients treated with DCV+ASV from August 2015 to September 2016 at five hospitals in the Daejeon-Chungcheong area. RESULTS: A total of 152 patients were examined for resistance associated variants (RAVs). Among them, 15 (9.9%) were positive for Y93 and one (0.7%) was positive for L31. Of 126 patients treated with DCV+ASV, 83 patients completed treatment and 76 patients were included in safety and efficacy analysis. Five (6.6%) were positive for Y93 and 12 (15.8%) exhibited cirrhotic change. DCV+ASV was the first-line treatment for 58 (76.3%) patients. Eleven (14.5%) patients relapsed after previous treatment that included interferon and seven (9.2%) of these patients were found to be intolerant of interferon. Adverse events occurred in 10 (13.2%) patients and two patients stopped the medication because of severe itching and skin rash. SVR12 was 89.5% (68/76) in all patients and 91.5% (65/71) in RAV-negative patients. CONCLUSIONS: DCV+ASV showed good efficacy in patients with HCV Ib infection in Korea. Close monitoring is needed for severe adverse events and treatment failure, which were uncommon.

Detection and characterization of primordial germ cells in pheasant (Phasianus colchicus) embryos.

The developmental similarity between the chicken and pheasant (Phasianus colchicus) allows the novel biotechnologies developed in the chicken to be applied to the production of transgenic pheasants and interspecies germline chimeras. To detect pheasant primordial germ cells (PGCs) efficiently, which is important for inducing germline transmission, the ultrastructure of PGCs and their reactivity to several antibodies (2C9, QB2, anti-SSEA-1, and QCR1) and periodic acid-Schiff's solution (PAS) were examined. To obtain PGCs, blood was taken from embryos incubated for 62-72 h or from gonads from embryos incubated for 156-216 h. The PGCs collected from both sources had the typical ultrastructure of pluripotent cells: a large nucleus with a distinct nucleolus, a high ratio of nuclear to cytoplasmic volume, and a distinct cytoplasmic membrane. In comparing the morphology of PGCs collected from different sites, more mitochondria and better-developed membrane microvilli were found in gonadal PGCs than in circulating PGCs. The nucleus of gonadal PGCs was flattened and had a large eccentrically positioned nucleolus. Of the antibodies tested, only QCR1 antibody reacted with an epitope in pheasant PGCs, and no specific signal was detected to other antibodies. The temporal change in the PGC populations in the blood and gonads of embryos was examined. In blood, the population was greater (P < 0.0001) in embryos incubated for 64 h than in embryos incubated for 62 or 66-72 h (31.4 versus 5.6-16.2 microL(-1)). In embryonic gonads, the number of PGCs increased continuously from 156 to 216 h of incubation (193-2,718 cells/embryo), although the ratio of PGCs to total gonadal cells did not change significantly (0.50-0.61%). In conclusion, pheasant PGCs have typical germ cell morphology and possess the QCR1 epitope. Circulating blood and the gonads of embryos incubated for 64 and 216 h, respectively, are good sources of PGCs.