Abstract
Most chemical vapor deposition methods for transition metal dichalcogenides use an extremely small amount of precursor to render large single-crystal flakes, which usually causes low ...coverage of the materials on the substrate. In this study, a self-capping vapor-liquid-solid reaction is proposed to fabricate large-grain, continuous MoS
2
films. An intermediate liquid phase-Na
2
Mo
2
O
7
is formed through a eutectic reaction of MoO
3
and NaF, followed by being sulfurized into MoS
2
. The as-formed MoS
2
seeds function as a capping layer that reduces the nucleation density and promotes lateral growth. By tuning the driving force of the reaction, large mono/bilayer (1.1 mm/200 μm) flakes or full-coverage films (with a record-high average grain size of 450 μm) can be grown on centimeter-scale substrates. The field-effect transistors fabricated from the full-coverage films show high mobility (33 and 49 cm
2
V
−1
s
−1
for the mono and bilayer regions) and on/off ratio (1 ~ 5 × 10
8
) across a 1.5 cm × 1.5 cm region.
In search of high-performance field-effect transistors (FETs) made of atomic thin semiconductors, indium selenide (InSe) has held great promise because of its high intrinsic mobility and moderate ...electronic band gap (1.26 eV). Yet the performance of InSe FETs is decisively determined by the surface oxidation of InSe taking place spontaneously in ambient conditions, setting up a mobility ceiling and causing an uncontrollable current hysteresis. Encapsulation by hexagonal boron nitride (h-BN) has been currently used to cope with this deterioration. Here, we provide insights into the role of surface oxides played in device performance and introduce a dry-oxidation process that forms a dense capping layer on top, where InSe FETs exhibit a record-high two-probe mobility of 423 cm2/V·s at room temperature and 1006 cm2/V·s at liquid nitrogen temperature without the use of h-BN encapsulation or high-κ dielectric screening. Ultrahigh on/off current ratio of >108 and current density of 365 μA/μm can be readily achieved without elaborate engineering of drain/source contacts or gating technique. Thickness-dependent device properties are also studied, with optimized performance shown in FETs comprising of 13 nm thick InSe. The high performance of InSe FETs with ultrathin dry oxide is attributed to the effective unpinning of the Fermi level at the metal contacts, resulting in a low Schottky barrier height of 40 meV in an optimized channel thickness.
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Recently, perovskite (PV) oxides with ABO3 structures have attracted considerable interest from scientists owing to their functionality. In this study, CaFeOx is introduced to reveal the resistive ...switching properties and mechanism of oxygen vacancy transition in PV and brownmillerite (BM) structures. BM‐CaFeO2.5 is grown on an Nb‐STO conductive substrate epitaxially. CaFeOx exhibits excellent endurance and reliability. In addition, the CaFeOx also demonstrates an electroforming‐free characteristic and multilevel resistance properties. To construct the switching mechanism, high‐resolution transmission electron microscopy is used to observe the topotactic phase change in CaFeOx. In addition, scanning TEM and electron energy loss spectroscopy show the structural evolution and valence state variation of CaFeOx after the switching behavior. This study not only reveals the switching mechanism of CaFeOx, but also provides a PV oxide option for the dielectric material in resistive random‐access memory (RRAM) devices.
A complex oxide CaFeOx (CFO) is introduced as the dielectric layer in resistive random‐access memory (RRAM), demonstrating excellent RRAM properties, such as electroforming‐free and multilevel data storage. This study provides not only the switching mechanism of the CFO RRAM devices, but also the novel aspect for the RRAM dielectric materials.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
The Forming phenomenon is observed via in situ transmission electron microscopy in the Ag/Ta2O5/Pt system. The device is switched to a low‐resistance state as the dual filament is connected to the ...electrodes. The results of energy dispersive spectrometer and electron energy loss spectroscopy analyses demonstrate that the filament is composed by a stack of oxygen vacancies and Ag metal.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Resistive random access memory (ReRAM) has been considered the most promising next-generation nonvolatile memory. In recent years, the switching behavior has been widely reported, and understanding ...the switching mechanism can improve the stability and scalability of devices. We designed an innovative sample structure for in situ transmission electron microscopy (TEM) to observe the formation of conductive filaments in the Pt/ZnO/Pt structure in real time. The corresponding current–voltage measurements help us to understand the switching mechanism of ZnO film. In addition, high-resolution transmission electron microscopy (HRTEM) and electron energy loss spectroscopy (EELS) have been used to identify the atomic structure and components of the filament/disrupted region, determining that the conducting paths are caused by the conglomeration of zinc atoms. The behavior of resistive switching is due to the migration of oxygen ions, leading to transformation between Zn-dominated ZnO1–x and ZnO.
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Abstract
Biohybrid neural interfaces (BHNIs) are a new class of neuromodulating devices that integrate neural microelectrode arrays (MEAs) and cell transplantation to improve treatment of nerve ...injuries and disorders. However, current BHNI devices are made from abiotic materials that are usually bio‐passive, non‐biodisintegratable, or rigid, which restricts encapsulated cell activity and host nerve reconstruction and frequently leads to local tissue inflammation. Herein, the first MEA composed of all disintegratable hydrogel tissue scaffold materials with synergistic performances of tissue conformal adhesiveness, MEA technologies, tissue scaffolding and stem cell therapy on a time scale appropriate for nerve tissue repair is proposed. In particular, the MEA conductive tracks are made from extracellular matrix (ECM)‐based double‐cross‐linked dual‐electrically conductive hydrogel (ECH) systems with robust tissue‐mimicking chemical/physical properties, electrical conductivity, and an affinity for neural progenitor stem cells. Meanwhile, the MEA hydrogel substrate prepared from transglutaminase‐incorporated gelatin/silk precursors simultaneously promotes gelation and interfacial adhesion between all MEA stacks, leading to rapid and scalable device integration. When the full hydrogel MEA is subjected to various mechanical stimuli and moisture, it is structurally stable with a low impedance (4 ± 3 kΩ) comparable to a recently reported benchmark. With seamless lamination around peripheral nerve fibers, the device permits successive neural signal monitoring for wound condition evaluation, while demonstrating synergistic effects of spatiotemporally controlled electrical stimulation and cell transplantation to accelerate restoration of motor function. This BHNI is completely degraded by 1 month thus eliminating the need for surgical retrieval to stably remain, interact, and further fuse with host tissues, successfully exhibiting compatible integration of biology and an implanted electrical system.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Stevens–Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN) are life‐threatening cutaneous conditions. However, studies of pediatric SJS/TEN are limited. To investigate the causes, clinical ...course, outcomes and complications of SJS and TEN in children. This retrospective study included 47 pediatric patients (aged < 18 years) with SJS, SJS/TEN, or TEN treated at Chang Gung Memorial Hospital, Taiwan, between January 2009 and December 2019. ALDEN scores and serological tests were used to assess causes and SCORTEN scores were applied to evaluate disease severity. Forty‐seven patients, including 30 with SJS, 6 with SJS/TEN, and 11 with TEN were included. Median age was 8 years (range 1–17 years); 51.1% were male. Thirty‐three cases (70.2%) were caused by drugs and infectious pathogens were suspected in 14 cases (29.8%). Oxcarbazepine (5/47, 10.6%) and amoxicillin (5/47, 10.6%) were the most often‐implicated drugs, and Mycoplasma infection (9/47, 19.1%) was the predominant infectious cause. Only one TENS patient died (mortality rate 1/47, 2.1%) due to septic shock with ARDS, acute renal failure and cardiopulmonary shock. Median hospital stay was 15.5 (3–42) days. Pulmonary involvement (2/39, 5.1%), including pneumonia and ARDS, was noted in acute stage. Long‐term sequelae were ocular involvement (6/39, 15.4%), nail dystrophy (4/39, 10.3%) and post‐inflammatory hypo‐/hyperpigmentation (3/39, 7.7%). In the present study, pediatric patients with SJS, SJS/TEN, or TEN have good outcomes with few long‐term complications and low mortality. Mycoplasma is the most common infectious cause in pediatric SJS/TEN. Ocular discomfort, nail dystrophy and skin dyschromia are common long‐term sequelae requiring regular follow‐up.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Understanding the magnetic and ferroelectric ordering of magnetoelectric multiferroic materials at the nanoscale necessitates a versatile imaging method with high spatial resolution. Here, soft X‐ray ...ptychography is employed to simultaneously image the ferroelectric and antiferromagnetic domains in an 80 nm thin freestanding film of the room‐temperature multiferroic BiFeO3 (BFO). The antiferromagnetic spin cycloid of period 64 nm is resolved by reconstructing the corresponding resonant elastic X‐ray scattering in real space and visualized together with mosaic‐like ferroelectric domains in a linear dichroic contrast image at the Fe L3 edge. The measurements reveal a near perfect coupling between the antiferromagnetic and ferroelectric ordering by which the propagation direction of the spin cycloid is locked orthogonally to the ferroelectric polarization. In addition, the study evinces both a preference for in‐plane propagation of the spin cycloid and changes of the ferroelectric polarization by 71° between multiferroic domains in the epitaxial strain‐free, freestanding BFO film. The results provide a direct visualization of the strong magnetoelectric coupling in BFO and of its fine multiferroic domain structure, emphasizing the potential of ptychographic imaging for the study of multiferroics and non‐collinear magnetic materials with soft X‐rays.
The ferroelectric and magnetic structure of a freestanding thin film of multiferroic bismuth ferrite are imaged with soft x‐ray ptychography at the Fe L‐edge. This scanning coherent diffractive imaging technique directly visualizes the strong magnetoelectric coupling between the antiferromagnetic spin cycloid and ferroelectric domains on the nanoscale.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Developing efficient bifunctional electrocatalysts in neutral media to avoid the deterioration of electrodes or catalysts under harsh environments has become the ultimate goal in electrochemical ...water splitting. This work demonstrates the fabrication of an on-chip bifunctional two-dimensional (2D) monolayer (ML) WSe2/graphene heterojunction microreactor for efficient overall water splitting in a neutral medium (pH = 7). Through the synergistic atomic growth of the metallic Cr dopant and graphene stitching contact on the 2D ML WSe2, the bifunctional WSe2/graphene heterojunction microreactor consisting of a full-cell configuration demonstrates excellent performance for overall water splitting in a neutral medium. Atomic doping of metallic Cr atoms onto the 2D ML WSe2 effectively facilitates the charge transfer at the solid–liquid interface. In addition, the direct growth of the self-stitching graphene contact with the 2D WSe2 catalyst largely reduces the contact resistance of the microreactor and further improves the overall water splitting efficiency. A significant reduction of the overpotential of nearly 1000 mV at 10 mA cm–2 at the Cr-doped WSe2/graphene heterojunction microreactor compared to the ML pristine WSe2 counterpart is achieved. The bifunctional WSe2/graphene self-stitching heterojunction microreactor is an ideal platform to investigate the fundamental mechanism of emerging bifunctional 2D catalysts for overall water splitting in a neutral medium.
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