Two-Step Conversion of Metal and Metal Oxide Precursor Films to 2D Transition Metal Dichalcogenides and Heterostructures.

The widely studied class of two-dimensional (2D) materials known as transition metal dichalcogenides (TMDs) are now well-poised to be employed in real-world applications ranging from electronic logic and memory devices to gas and biological sensors. Several scalable thin film synthesis techniques have demonstrated nanoscale control of TMD material thickness, morphology, structure, and chemistry and correlated these properties with high-performing, application-specific device metrics. In this review, the particularly versatile two-step conversion (2SC) method of TMD film synthesis is highlighted. The 2SC technique relies on deposition of a solid metal or metal oxide precursor material, followed by a reaction with a chalcogen vapor at an elevated temperature, converting the precursor film to a crystalline TMD. Herein, the variables at each step of the 2SC process including the impact of the precursor film material and deposition technique, the influence of gas composition and temperature during conversion, as well as other factors controlling high-quality 2D TMD synthesis are considered. The specific advantages of the 2SC approach including deposition on diverse substrates, low-temperature processing, orientation control, and heterostructure synthesis, among others, are featured. Finally, emergent opportunities that take advantage of the 2SC approach are discussed to include next-generation electronics, sensing, and optoelectronic devices, as well as catalysis for energy-related applications.

Orientation and morphology control in acid-catalyzed covalent organic framework thin films.

As thin films of semiconducting covalent organic frameworks (COFs) are demonstrating utility for ambipolar electronics, channel materials in organic electrochemical transistors (OECTs), and broadband photodetectors, control and modulation of their thin film properties is paramount. In this work, an interfacial growth technique is utilized to synthesize imine TAPB-PDA COF films at both the liquid-liquid interface as well as at the liquid-solid interface on a Si/SiO2 substrate. The concentration of acetic acid catalyst in the aqueous phase is shown to significantly influence the thin film morphology of the liquid-solid growth, with concentrations below 1 M resulting in no film nucleation, concentrations of 1-4 M enabling smooth film formation, and concentrations greater than 4 M resulting in films with a higher density of particulates on the surface. Importantly, while the films grown at the liquid-liquid interface are mixed-orientation, those grown directly at the liquid-solid interface on the Si/SiO2 surface have highly oriented COF layers aligned parallel to the substrate surface. Moreover, this liquid-solid growth process affords TAPB-PDA COF thin films with p-type charge transport having a transconductance of 10 µS at a gate voltage of -0.9 V in an OECT device structure.

Laser-Fabricated 2D Molybdenum Disulfide Electronic Sensor Arrays for Rapid, Low-Cost, Ultrasensitive Detection of Influenza A and SARS-Cov-2.

Multiplex electronic antigen sensors for detection of SARS-Cov-2 spike glycoproteins and hemagglutinin from influenza A are fabricated using scalable processes for straightforward transition to economical mass-production. The sensors utilize the sensitivity and surface chemistry of a 2D MoS2 transducer for attachment of antibody fragments in a conformation favorable for antigen binding with no need for additional linker molecules. To make the devices, ultra-thin layers (3 nm) of amorphous MoS2 are sputtered over pre-patterned metal electrical contacts on a glass chip at room temperature. The amorphous MoS2 is then laser annealed to create an array of semiconducting 2H-MoS2 transducer regions between metal contacts. The semiconducting crystalline MoS2 region is functionalized with monoclonal antibody fragments complementary to either SARS-CoV-2 S1 spike protein or influenza A hemagglutinin. Quartz crystal microbalance experiments indicate strong binding and maintenance of antigen avidity for antibody fragments bound to MoS2. Electrical resistance measurements of sensors exposed to antigen concentrations ranging from 2-20 000 pg mL-1 reveal selective responses. Sensor architecture is adjusted to produce an array of sensors on a single chip suited for detection of analyte concentrations spanning six orders of magnitude from pg mL-1 to µg mL-1.

Light-matter coupling in large-area van der Waals superlattices.

Two-dimensional (2D) crystals have renewed opportunities in design and assembly of artificial lattices without the constraints of epitaxy. However, the lack of thickness control in exfoliated van der Waals (vdW) layers prevents realization of repeat units with high fidelity. Recent availability of uniform, wafer-scale samples permits engineering of both electronic and optical dispersions in stacks of disparate 2D layers with multiple repeating units. Here we present optical dispersion engineering in a superlattice structure comprising alternating layers of 2D excitonic chalcogenides and dielectric insulators. By carefully designing the unit cell parameters, we demonstrate greater than 90% narrow band absorption in less than 4 nm of active layer excitonic absorber medium at room temperature, concurrently with enhanced photoluminescence in square-centimetre samples. These superlattices show evidence of strong light-matter coupling and exciton-polariton formation with geometry-tuneable coupling constants. Our results demonstrate proof of concept structures with engineered optical properties and pave the way for a broad class of scalable, designer optical metamaterials from atomically thin layers.

Direct Optoelectronic Imaging of 2D Semiconductor-3D Metal Buried Interfaces.

The semiconductor-metal junction is one of the most critical factors for high-performance electronic devices. In two-dimensional (2D) semiconductor devices, minimizing the voltage drop at this junction is particularly challenging and important. Despite numerous studies concerning contact resistance in 2D semiconductors, the exact nature of the buried interface under a three-dimensional (3D) metal remains unclear. Herein, we report the direct measurement of electrical and optical responses of 2D semiconductor-metal buried interfaces using a recently developed metal-assisted transfer technique to expose the buried interface, which is then directly investigated using scanning probe techniques. We characterize the spatially varying electronic and optical properties of this buried interface with <20 nm resolution. To be specific, potential, conductance, and photoluminescence at the buried metal/MoS2 interface are correlated as a function of a variety of metal deposition conditions as well as the type of metal contacts. We observe that direct evaporation of Au on MoS2 induces a large strain of ∼5% in the MoS2 which, coupled with charge transfer, leads to degenerate doping of the MoS2 underneath the contact. These factors lead to improvement of contact resistance to record values of 138 kΩ µm, as measured using local conductance probes. This approach was adopted to characterize MoS2-In/Au alloy interfaces, demonstrating contact resistance as low as 63 kΩ µm. Our results highlight that the MoS2/metal interface is sensitive to device fabrication methods and provide a universal strategy to characterize buried contact interfaces involving 2D semiconductors.

Transferrable AlGaN/GaN High-Electron Mobility Transistors to Arbitrary Substrates via a Two-Dimensional Boron Nitride Release Layer.

Mechanical transfer of high-performing thin-film devices onto arbitrary substrates represents an exciting opportunity to improve device performance, explore nontraditional manufacturing approaches, and paves the way for soft, conformal, and flexible electronics. Using a two-dimensional boron nitride release layer, we demonstrate the transfer of AlGaN/GaN high-electron mobility transistors (HEMTs) to arbitrary substrates through both direct van der Waals bonding and with a polymer adhesive interlayer. No device degradation was observed because of the transfer process, and a significant reduction in device temperature (327-132 °C at 600 mW) was observed when directly bonded to a silicon carbide (SiC) wafer relative to the starting wafer. With the use of a benzocyclobutene (BCB) adhesion interlayer, devices were easily transferred and characterized on Kapton and ceramic films, representing an exciting opportunity for integration onto arbitrary substrates. Upon reduction of this polymer adhesive layer thickness, the AlGaN/GaN HEMTs transferred onto a BCB/SiC substrate resulted in comparable peak temperatures during operation at powers as high as 600 mW to the as-grown wafer, revealing that by optimizing interlayer characteristics such as thickness and thermal conductivity, transferrable devices on polymer layers can still improve performance outputs.

Two-Dimensional Materials in Biosensing and Healthcare: From In Vitro Diagnostics to Optogenetics and Beyond.

Since the isolation of graphene in 2004, there has been an exponentially growing number of reports on layered two-dimensional (2D) materials for applications ranging from protective coatings to biochemical sensing. Due to the exceptional, and often tunable, electrical, optical, electrochemical, and physical properties of these materials, they can serve as the active sensing element or a supporting substrate for diverse healthcare applications. In this review, we provide a survey of the recent reports on the applications of 2D materials in biosensing and other emerging healthcare areas, ranging from wearable technologies to optogenetics to neural interfacing. Specifically, this review provides (i) a holistic evaluation of relevant material properties across a wide range of 2D systems, (ii) a comparison of 2D material-based biosensors to the state-of-the-art, (iii) relevant material synthesis approaches specifically reported for healthcare applications, and (iv) the technological considerations to facilitate mass production and commercialization.

Photonic crystallization of two-dimensional MoS2 for stretchable photodetectors.

Low temperature synthesis of high quality two-dimensional (2D) materials directly on flexible substrates remains a fundamental limitation towards scalable realization of robust flexible electronics possessing the unique physical properties of atomically thin structures. Herein, we describe room temperature sputtering of uniform, stoichiometric amorphous MoS2 and subsequent large area (>6.25 cm2) photonic crystallization of 5 nm 2H-MoS2 films in air to enable direct, scalable fabrication of ultrathin 2D photodetectors on stretchable polydimethylsiloxane (PDMS) substrates. The lateral photodetector devices demonstrate an average responsivity of 2.52 µW A-1 and a minimum response time of 120 ms under 515.6 nm illumination. Additionally, the surface wrinkled, or buckled, PDMS substrate with conformal MoS2 retained the photoconductive behavior at tensile strains as high as 5.72% and over 1000 stretching cycles. The results indicate that the photonic crystallization method provides a significant advancement in incorporating high quality semiconducting 2D materials applied directly on polymer substrates for wearable and flexible electronic systems.

Examining the role of extracorporeal membrane oxygenation in patients following suspected or confirmed suicide attempts: A case series.

The decision to offer extracorporeal membrane oxygenation (ECMO) is based on a risk/benefit assessment and the likelihood of a treatable underlying condition or the feasibility of destination therapy (durable mechanical support or thoracic organ transplantation) should heart-lung function fail to improve. Patients who present following suspected suicide attempts who fail medical therapy may pose a dilemma for clinicians. An assessment to determine if a patient has a high likelihood of psychiatric recovery such that bridging with ECMO or ultimately destination therapy could or should be offered is not always feasible in the setting of critical illness. This case series reviews our institution's experience with ECMO in the management of five patients who presented following suspected or confirmed suicide attempts. All five patients survived to hospital discharge. Two had subsequent psychiatric admissions, one following a repeat suicide attempt. A discussion of these cases demonstrates the effectiveness of ECMO in supporting this group of patients in the short-term. The self-limited natural history of many psychiatric episodes, poisonings and traumatic injuries makes the use of ECMO a potentially reasonable support strategy. However, careful consideration must be given to psychiatric history and follow-up given the substantial commitment of resources, potential for complications and for stranding patients on extracorporeal therapy without definitive destination therapy.

M1 Macrophage-Induced Endothelial-to-Mesenchymal Transition Promotes Infantile Hemangioma Regression.

Infantile hemangiomas are benign tumors of vascular endothelial cells (ECs), characterized by three distinct stages: proliferating phase, involuting phase, and involuted phase. The mechanisms that trigger involution of hemangioma into fibro-fatty tissue remain unknown. We report a novel mechanism by which M1-polarized macrophages induce endothelial-to-mesenchymal transition (EndMT) and promote hemangioma regression. M1- but not M2-polarized macrophages induced EndMT in ECs. Tumor necrosis factor-α and, to a lesser extent, IL-1ß and interferon-γ were the most potent cytokines produced by the M1 macrophages that induce in vitro EndMT. Western blot analysis and gene expression profiling showed that ECs treated with M1 macrophages, tumor necrosis factor-α, or IL-1ß decreased the expression of endothelial markers, whereas mesenchymal markers increased concomitantly. Immunohistochemical staining of patient samples revealed that a significant perivascular infiltration of M1, but not M2, macrophages coincides with endothelial expression of the critical EndMT transcription factors Snail/Slug in involuting hemangiomas. Most strikingly, M1 macrophage-treated ECs isolated from patient hemangiomas (HemECs) but not untreated HemECs readily differentiated into adipocytes on adipogenic induction. Thus, in vitro EndMT and adipogenesis of HemECs have, in part, recapitulated the natural history of hemangioma regression. In conclusion, our findings indicate that EndMT induced by M1 macrophages promotes infantile hemangioma regression and may lead to novel therapeutic treatments for this vascular tumor.

Nonoperative treatment of acute appendicitis in children: A feasibility study.

PURPOSE: Nonoperative treatment of acute appendicitis appears to be feasible in adults. It is unclear whether the same is true for children. METHODS: Children 5-18 years with <48 h symptoms of acute appendicitis were offered nonoperative treatment: 2 doses of piperacillin IV, then ampicillin/clavulanate ×1 week. Treatment failure (worsening on therapy) and recurrence (after completion of therapy) were noted. Patients who declined enrollment were asked to participate as controls. Cost-utility analysis was performed using Pediatric Quality of Life Scale (PedsQL®) to calculate quality-adjusted life month (QALM) for study and control patients. RESULTS: Twenty-four patients agreed to undergo nonoperative management, and 50 acted as controls. At a mean follow-up of 14 months, three of the 24 failed on therapy, and 2/21 returned with recurrent appendicitis at 43 and 52 days, respectively. Two patients elected to undergo an interval appendectomy despite absence of symptoms. Appendectomy-free rate at one year was therefore 71% (C.I. 50-87%). No patient developed perforation or other complications. Cost-utility analysis shows a 0.007-0.03 QALM increase and a $1359 savings from $4130 to $2771 per nonoperatively treated patient. CONCLUSION: Despite occasional late recurrences, antibiotic-only treatment of early appendicitis in children is feasible, safe, cost-effective and is experienced more favorably by patients and parents.

Enterovirus D68 and Panton-Valentine Leukocidin-Positive Staphylococcus aureus Respiratory Coinfection with Fatal Outcome.

A previously healthy 10-year-old girl with a 2-day history of upper respiratory illness and fever rapidly developed respiratory failure and sepsis with leukopenia, and expired despite attempts at resuscitation. Postmortem examination revealed bilateral necrotizing pneumonia and evidence of disseminated intravascular coagulation. Nasopharyngeal swabs and lung tissue submitted to the Centers for Disease Control and Prevention (CDC) were positive for Enterovirus D68 (EV-D68). Blood and lung cultures were positive for methicillin-resistant Staphylococcus aureus (MRSA). The isolates were submitted to the CDC and were found to be positive for the toxin Panton-Valentine leukocidin. We describe a fatality related to invasive toxin-mediated MRSA associated with EV-D68 coinfection, along with the clinical, laboratory, and autopsy findings, which provided important clues, prompting further investigation at the CDC to arrive at the correct diagnosis.

Iatrogenic Preterm Premature Rupture of Membranes after Fetoscopic Laser Ablative Surgery.

INTRODUCTION: To describe the incidence and risk factors for iatrogenic premature preterm rupture of membranes (iPPROM) after fetoscopic laser surgery for the twin-to-twin-transfusion syndrome. MATERIALS AND METHODS: This is a retrospective review of all patients who have undergone fetoscopic laser surgery at a single fetal treatment center since 2000. We defined iPPROM as spontaneous rupture of membranes before the onset of labor prior to 34 weeks of gestation. The iPPROM cohort was compared to the cohort without iPPROM for several preoperative, operative, and delivery characteristics. RESULTS: Ninety-two consecutive patients were reviewed. The overall rate of iPPROM was 18.5% (n = 17). The rates of iPPROM within 1 and 4 weeks were 5.4 and 10.9%, respectively. The median interval from surgery to delivery was significantly shorter in the iPPROM group (21 vs. 62 days, p = 0.01). The mean gestational age at delivery (27.0 vs. 31.1 weeks, p = 0.02) was lower in the iPPROM group. No other characteristics studied differed significantly between the groups. DISCUSSION: The incidence of iPPROM was substantially lower than in recent multicenter reports; however, no risk factors of iPPROM could be identified. Whether this is related to variations in surgical or anesthetic management will require further investigation.

Extracorporeal life support in critically ill adults.

Extracorporeal life support (ECLS) has become increasingly popular as a salvage strategy for critically ill adults. Major advances in technology and the severe acute respiratory distress syndrome that characterized the 2009 influenza A(H1N1) pandemic have stimulated renewed interest in the use of venovenous extracorporeal membrane oxygenation (ECMO) and extracorporeal carbon dioxide removal to support the respiratory system. Theoretical advantages of ECLS for respiratory failure include the ability to rest the lungs by avoiding injurious mechanical ventilator settings and the potential to facilitate early mobilization, which may be advantageous for bridging to recovery or to lung transplantation. The use of venoarterial ECMO has been expanded and applied to critically ill adults with hemodynamic compromise from a variety of etiologies, beyond postcardiotomy failure. Although technology and general care of the ECLS patient have evolved, ECLS is not without potentially serious complications and remains unproven as a treatment modality. The therapy is now being tested in clinical trials, although numerous questions remain about the application of ECLS and its impact on outcomes in critically ill adults.

Maternal and fetal safety of fluid-restrictive general anesthesia for endoscopic fetal surgery in monochorionic twin gestations.

STUDY OBJECTIVE: To review our experience with general anesthesia in endoscopic fetal surgery for twin-to-twin transfusion syndrome (TTTS), and to compare fetomaternal outcome before and after protocol implementation. DESIGN: Retrospective impact study. SETTING: University-affiliated medical center. MEASUREMENTS: Data from 85 consecutive patients who underwent endoscopic laser ablation of placenta vessels for severe TTTS were studied. Outcomes were compared in patients before (2000-2007) and after (2008-2012) a change to strict intraoperative intravenous (IV) fluid and liberal vasopressor management. Perioperative parameters (IV fluid administration, vasopressor use, maternal hemoglobin [Hb] concentration); maternal complication rate (respiratory, hemorrhagic); pregnancy outcome; and fetal and neonatal survival were recorded. MAIN RESULTS: Patients in the early group (2000-2007; n = 55) received 1634 ± 949 mL of crystalloid fluid intraoperatively, compared with 485 ± 238 mL (P < 0.001; Student's t test) given to the late group (2008-2012; n = 30). Maternal pulmonary edema and any respiratory distress were seen in 5.5% and 12.7% of patients in the early group, respectively, and in none of the late group patients (P < 0.05; Chi-square analysis). CONCLUSIONS: A significant risk of maternal respiratory complications exists after general anesthesia for endoscopic fetal surgery. Judicious fluid management significantly decreases this risk.

Photo-sensitivity of large area physical vapor deposited mono and bilayer MoS2.

We present photosensitivity in large area physical vapour deposited mono and bi-layer MoS2 films. Photo-voltaic effect was observed in single layer MoS2 without any apparent rectifying junctions, making device fabrication straightforward. For bi-layers, no such effect was present, suggesting strong size effect in light-matter interaction. The photo-voltaic effect was observed to highly direction dependent in the film plane, which suggests that the oblique deposition configuration plays a key role in developing the rectifying potential gradient. To the best of our knowledge, this is the first report of any large area and transfer free MoS2 photo device with performance comparable to their exfoliated counterparts.