Ambipolar charge-transfer graphene plasmonic cavities.

Plasmon polaritons in van der Waals materials hold promise for various photonics applications1-4. The deterministic imprinting of spatial patterns of high carrier density in plasmonic cavities and nanoscale circuitry can enable the realization of advanced nonlinear nanophotonic5 and strong light-matter interaction platforms6. Here we demonstrate an oxidation-activated charge transfer strategy to program ambipolar low-loss graphene plasmonic structures. By covering graphene with transition-metal dichalcogenides and subsequently oxidizing the transition-metal dichalcogenides into transition-metal oxides, we activate charge transfer rooted in the dissimilar work functions between transition-metal oxides and graphene. Nano-infrared imaging reveals ambipolar low-loss plasmon polaritons at the transition-metal-oxide/graphene interfaces. Further, by inserting dielectric van der Waals spacers, we can precisely control the electron and hole densities induced by oxidation-activated charge transfer and achieve plasmons with a near-intrinsic quality factor. Using this strategy, we imprint plasmonic cavities with laterally abrupt doping profiles with nanoscale precision and demonstrate plasmonic whispering-gallery resonators based on suspended graphene encapsulated in transition-metal oxides.

Nonlinear nanoelectrodynamics of a Weyl metal.

Chiral Weyl fermions with linear energy-momentum dispersion in the bulk accompanied by Fermi-arc states on the surfaces prompt a host of enticing optical effects. While new Weyl semimetal materials keep emerging, the available optical probes are limited. In particular, isolating bulk and surface electrodynamics in Weyl conductors remains a challenge. We devised an approach to the problem based on near-field photocurrent imaging at the nanoscale and applied this technique to a prototypical Weyl semimetal TaIrTe4 As a first step, we visualized nano-photocurrent patterns in real space and demonstrated their connection to bulk nonlinear conductivity tensors through extensive modeling augmented with density functional theory calculations. Notably, our nanoscale probe gives access to not only the in-plane but also the out-of-plane electric fields so that it is feasible to interrogate all allowed nonlinear tensors including those that remained dormant in conventional far-field optics. Surface- and bulk-related nonlinear contributions are distinguished through their "symmetry fingerprints" in the photocurrent maps. Robust photocurrents also appear at mirror-symmetry breaking edges of TaIrTe4 single crystals that we assign to nonlinear conductivity tensors forbidden in the bulk. Nano-photocurrent spectroscopy at the boundary reveals a strong resonance structure absent in the interior of the sample, providing evidence for elusive surface states.

Quenched Excitons in WSe2/α-RuCl3 Heterostructures Revealed by Multimessenger Nanoscopy.

We investigate heterostructures composed of monolayer WSe2 stacked on α-RuCl3 using a combination of Terahertz (THz) and infrared (IR) nanospectroscopy and imaging, scanning tunneling spectroscopy (STS), and photoluminescence (PL). Our observations reveal itinerant carriers in the heterostructure prompted by charge transfer across the WSe2/α-RuCl3 interface. Local STS measurements show the Fermi level is shifted to the valence band edge of WSe2 which is consistent with p-type doping and verified by density functional theory (DFT) calculations. We observe prominent resonances in near-IR nano-optical and PL spectra, which are associated with the A-exciton of WSe2. We identify a concomitant, near total, quenching of the A-exciton resonance in the WSe2/α-RuCl3 heterostructure. Our nano-optical measurements show that the charge-transfer doping vanishes while excitonic resonances exhibit near-total recovery in "nanobubbles", where WSe2 and α-RuCl3 are separated by nanometer distances. Our broadband nanoinfrared inquiry elucidates local electrodynamics of excitons and an electron-hole plasma in the WSe2/α-RuCl3 system.

Efficient Avalanche Photodiodes with a WSe2/MoS2 Heterostructure via Two-Photon Absorption.

Two-dimensional (2D) materials-based photodetectors in the infrared range hold the key to enabling a wide range of optoelectronics applications including infrared imaging and optical communications. While there exist 2D materials with a narrow bandgap sensitive to infrared photons, a two-photon absorption (TPA) process can also enable infrared photodetection in well-established 2D materials with large bandgaps such as WSe2 and MoS2. However, most of the TPA photodetectors suffer from low responsivity, preventing this method from being widely adopted for infrared photodetection. Herein, we experimentally demonstrate 2D materials-based TPA avalanche photodiodes achieving an ultrahigh responsivity. The WSe2/MoS2 heterostructure absorbs infrared photons with an energy smaller than the material bandgaps via a low-efficiency TPA process. The significant avalanche effect with a gain of ∼1300 improves the responsivity, resulting in the record-high responsivity of 88 µA/W. We believe that this work paves the way toward building practical and high-efficiency 2D materials-based infrared photodetectors.

Clinical course in patients with chronic undifferentiated arthritis of the elbow after arthroscopic synovectomy.

BACKGROUND: Surgical treatment can be considered for patients with undifferentiated arthritis (UA) limited to the elbow joint. The purpose of this study was to analyze the clinical outcomes of arthroscopic synovectomy. METHODS: Nineteen patients who underwent arthroscopic synovectomy for chronic UA of the elbow between 2006 and 2019 were enrolled in this study. One patient was excluded because of evidence of tuberculosis in the biopsy. Chronic UA of the elbow was defined as (1) localized synovitis diagnosed by magnetic resonance imaging, (2) no specific cause, and (3) no response to conservative treatment for >3 months. We compared baseline characteristics and clinical outcomes between the remission and disease progression groups. RESULTS: Postoperatively, synovitis was controlled in 13 patients. In 5 patients, the symptoms disappeared after surgery without any medical treatment. Four patients discontinued disease-modifying antirheumatic drugs. Nine patients were classified as in remission. The disease progression group had a longer symptom duration, elevated rheumatoid markers, and higher Larsen grading. However, the difference was not statistically significant. CONCLUSIONS: Arthroscopic synovectomy achieved remission in approximately 47% of patients with chronic UA of the elbow. Although arthroscopic synovectomy did not prevent RA, it can be considered for rapid resolution of synovitis and diagnostic purposes.

Evaluation of analgesic efficacy and opioid sparing effect of pregabalin after arthroscopic rotator cuff repair surgery: A retrospective cohort study.

BACKGROUND: Considering the adverse effects of opioids, it is essential to minimize their consumption for postoperative pain control. Studies have reported the opioid sparing effects of pregabalin, with conflicting results. Evidence for administering pregabalin in a multimodal regimen after arthroscopic rotator cuff repair surgery is limited. METHODS: A total of 64 patients who underwent arthroscopic rotator cuff repair were enrolled in the cohort, and their data were retrospectively analyzed to evaluate the ability of pregabalin for postoperative analgesia and opioid sparing. The pregabalin group (n = 32) received additional pregabalin 75 mg for 2 weeks from the day before the surgery with the standard pain medications; in contrast, the control group (n = 32) was prescribed the standard pain medications alone. The total volume of patient-controlled anesthesia, doses of oral oxycodone and intravenous morphine as rescue analgesics, number of adverse events, and patient satisfaction based on the numeric rating scale (0-10) were assessed. Further, we used the visual analog scale for evaluating pain and function for 6 months in each group. RESULTS: Total patient-controlled anesthesia volume, number of patient-controlled anesthesia attempts on the day of surgery, and total oral oxycodone consumption were significantly lower in the pregabalin group. Visual analog scale scores for pain and function showed no significant differences. Although the total number of adverse effects (nausea, vomiting, dizziness, dry mouth, urinary retention, itching sense, or constipation) was higher in the pregabalin group than in the control group, the difference was not statistically significant. CONCLUSION: Our multimodal regimen with pregabalin significantly reduced opioid consumption with similar adverse effects. However, there was no significant difference in the pain score. We recommend pregabalin as an additional analgesic for arthroscopic rotator cuff repairs, especially for medium to large sized tears.

Disorder in van der Waals heterostructures of 2D materials.

Realizing the full potential of any materials system requires understanding and controlling disorder, which can obscure intrinsic properties and hinder device performance. Here we examine both intrinsic and extrinsic disorder in two-dimensional (2D) materials, in particular graphene and transition metal dichalcogenides (TMDs). Minimizing disorder is crucial for realizing desired properties in 2D materials and improving device performance and repeatability for practical applications. We discuss the progress in disorder control for graphene and TMDs, as well as in van der Waals heterostructures realized by combining these materials with hexagonal boron nitride. Furthermore, we showcase how atomic defects or disorder can also be harnessed to provide useful electronic, optical, chemical and magnetic functions.

Probing graphene grain boundaries with optical microscopy.

Grain boundaries in graphene are formed by the joining of islands during the initial growth stage, and these boundaries govern transport properties and related device performance. Although information on the atomic rearrangement at graphene grain boundaries can be obtained using transmission electron microscopy and scanning tunnelling microscopy, large-scale information regarding the distribution of graphene grain boundaries is not easily accessible. Here we use optical microscopy to observe the grain boundaries of large-area graphene (grown on copper foil) directly, without transfer of the graphene. This imaging technique was realized by selectively oxidizing the underlying copper foil through graphene grain boundaries functionalized with O and OH radicals generated by ultraviolet irradiation under moisture-rich ambient conditions: selective diffusion of oxygen radicals through OH-functionalized defect sites was demonstrated by density functional calculations. The sheet resistance of large-area graphene decreased as the graphene grain sizes increased, but no strong correlation with the grain size of the copper was revealed, in contrast to a previous report. Furthermore, the influence of graphene grain boundaries on crack propagation (initialized by bending) and termination was clearly visualized using our technique. Our approach can be used as a simple protocol for evaluating the grain boundaries of other two-dimensional layered structures, such as boron nitride and exfoliated clays.

Low-Temperature Ohmic Contact to Monolayer MoS2 by van der Waals Bonded Co/h-BN Electrodes.

Monolayer MoS2, among many other transition metal dichalcogenides, holds great promise for future applications in nanoelectronics and optoelectronics due to its ultrathin nature, flexibility, sizable band gap, and unique spin-valley coupled physics. However, careful study of these properties at low temperature has been hindered by an inability to achieve low-temperature Ohmic contacts to monolayer MoS2, particularly at low carrier densities. In this work, we report a new contact scheme that utilizes cobalt (Co) with a monolayer of hexagonal boron nitride (h-BN) that has the following two functions: modifies the work function of Co and acts as a tunneling barrier. We measure a flat-band Schottky barrier of 16 meV, which makes thin tunnel barriers upon doping the channels, and thus achieve low-T contact resistance of 3 kΩ.µm at a carrier density of 5.3 × 1012/cm2. This further allows us to observe Shubnikov-de Haas oscillations in monolayer MoS2 at much lower carrier densities compared to previous work.

Reverse Sural Artery Island Flap With Skin Extension Along the Pedicle.

The distally based sural flap is an efficient flap for reconstruction of soft tissues defects of lower limb. The unstable vascular pedicle, however, is prone to compression by the subcutaneous tunnel, especially when a long pedicle covers the distal area of the foot. The aim of the present study was to introduce a modified surgical technique that leaves the skin extension over the pedicle and to report the clinical results of this modification. A total of 25 consecutive patients with a mean age of 51.7 ± 14.7 years underwent surgery. We modified the conventional sural flap technique by leaving a skin extension over the entire length of the pedicle, creating a fasciocutaneous vascular pedicle. The postoperative flap survival rates, complications, and the characteristics of the flaps such as flap size, pedicle length, and the most distal area that could be covered with this modification, were reviewed. At the last clinical follow-up examination, all the flaps survived, although partial necrosis was observed in 2 (8%) cases. Four cases of venous congestion developed but healed without additional complications. The mean flap size was 5.9 ± 1.8 × 9.2 ± 2.7 cm. With this modification, the sural flap could cover the defect located in extreme distal areas, such as the medial forefoot and dorsum of the first metatarsophalangeal joint, with a longer pedicle (≤27 cm) in 7 patients (28%). A skin extension along the pedicle achieved the favorable survival rate of the sural flap and successfully extended the surgical indications to more distal areas.

The sagittal plane angle and tunnel-related complications in double-bundle anterior cruciate ligament reconstruction using the transportal technique: an in vivo imaging study.

PURPOSE: To evaluate the relation between the tunnel angle in the 3 orthogonal planes, especially the sagittal plane, which can be influenced by knee flexion during drilling, and the incidence of complications from the transportal technique using in vivo imaging data. METHODS: Fifty-one patients who underwent anatomic double-bundle anterior cruciate ligament reconstruction by the transportal technique were evaluated retrospectively. A 3-dimensional surface model was made using an axial computed tomography scan obtained after anterior cruciate ligament reconstruction. The tunnel length, posterior cortical damage, proximity between the outer orifice of the tunnel and lateral collateral ligament (LCL) origin, and medial femoral condyle cartilage damage were evaluated on a 3-dimensional computed tomography scan and 3-T magnetic resonance imaging. Correlations between those parameters and the tunnel angle in the coronal, axial, and sagittal planes were analyzed. RESULTS: A tunnel length of less than 30 mm developed in 4 cases (8%) in the anteromedial tunnel and in 1 case (2%) in the posterolateral (PL) tunnel. Posterior cortical damage developed in 12 cases (23%). A distance from the outer orifice of the tunnel to the LCL origin of less than 3 mm occurred in 18 cases (35.2%) in the PL tunnel. Medial femoral condyle cartilage damage was detected in 3 cases (6%). A positive correlation was observed between the sagittal angle and anteromedial tunnel length (P = .002, r = 0.547). The sagittal angle in the group with posterior cortical damage was lower than that in the group with no posterior cortical damage (P = .002). A negative correlation was observed between the distance from the outer orifice of the PL tunnel to the LCL origin and the sagittal angle (P = .002, r = -0.55). CONCLUSIONS: Drilling at a higher angle in the sagittal plane decreased the incidence of posterior cortical damage and a short anteromedial tunnel. However, drilling at a higher angle shortened the distance to the LCL origin for the PL tunnel. LEVEL OF EVIDENCE: Level IV, therapeutic case series.

Transferred wrinkled Al2O3 for highly stretchable and transparent graphene-carbon nanotube transistors.

Despite recent progress in producing transparent and bendable thin-film transistors using graphene and carbon nanotubes, the development of stretchable devices remains limited either by fragile inorganic oxides or polymer dielectrics with high leakage current. Here we report the fabrication of highly stretchable and transparent field-effect transistors combining graphene/single-walled carbon nanotube (SWCNT) electrodes and a SWCNT-network channel with a geometrically wrinkled inorganic dielectric layer. The wrinkled Al2O3 layer contained effective built-in air gaps with a small gate leakage current of 10(-13) A. The resulting devices exhibited an excellent on/off ratio of ~10(5), a high mobility of ~40 cm(2) V(-1) s(-1) and a low operating voltage of less than 1 V. Importantly, because of the wrinkled dielectric layer, the transistors retained performance under strains as high as 20% without appreciable leakage current increases or physical degradation. No significant performance loss was observed after stretching and releasing the devices for over 1,000 times. The sustainability and performance advances demonstrated here are promising for the adoption of stretchable electronics in a wide variety of future applications.

Advances and Applications of Oxidized van der Waals Transition Metal Dichalcogenides.

The surface oxidation of 2D transition metal dichalcogenides (TMDs) has recently gained tremendous technological and fundamental interest owing to the multi-functional properties that the surface oxidized layer opens up. In particular, when integrated into other 2D materials in the form of van der Waals heterostructures, oxidized TMDs enable designer properties, including novel electronic states, engineered light-matter interactions, and exceptional-point singularities, among many others. Here, the evolving landscapes of the state-of-the-art surface engineering technologies that enable controlled oxidation of TMDs down to the monolayer-by-monolayer limit are reviewed. Next, the use of oxidized TMDs in van der Waals heterostructures for different electronic and photonic device platforms, materials growth processes, engineering concepts, and synthesizing new condensed matter phenomena is discussed. Finally, challenges and outlook for future impact of oxidized TMDs in driving rapid advancements across various application fronts is discussed.

Unzipping hBN with ultrashort mid-infrared pulses.

Manipulating the nanostructure of materials is critical for numerous applications in electronics, magnetics, and photonics. However, conventional methods such as lithography and laser writing require cleanroom facilities or leave residue. We describe an approach to creating atomically sharp line defects in hexagonal boron nitride (hBN) at room temperature by direct optical phonon excitation with a mid-infrared pulsed laser from free space. We term this phenomenon "unzipping" to describe the rapid formation and growth of a crack tens of nanometers wide from a point within the laser-driven region. Formation of these features is attributed to the large atomic displacement and high local bond strain produced by strongly driving the crystal at a natural resonance. This process occurs only via coherent phonon excitation and is highly sensitive to the relative orientation of the crystal axes and the laser polarization. Its cleanliness, directionality, and sharpness enable applications such as polariton cavities, phonon-wave coupling, and in situ flake cleaving.

Extraordinary Enhancement of Nonlinear Optical Interaction in NbOBr2 Microcavities.

2D materials are burgeoning as promising candidates for investigating nonlinear optical effects due to high nonlinear susceptibilities, broadband optical response, and tunable nonlinearity. However, most 2D materials suffer from poor nonlinear conversion efficiencies, resulting from reduced light-matter interactions and lack of phase matching at atomic thicknesses. Herein, a new 2D nonlinear material, niobium oxide dibromide (NbOBr2) is reported, featuring strong and anisotropic optical nonlinearities with scalable nonlinear intensity. Furthermore, Fabry-Pérot (F-P) microcavities are constructed by coupling NbOBr2 with air holes in silicon. Remarkable enhancement factors of ≈630 times in second harmonic generation (SHG) and 210 times in third harmonic generation (THG) are achieved on cavity at the resonance wavelength of 1500 nm. Notably, the cavity enhancement effect exhibits strong anisotropic feature tunable with pump wavelength, owing to the robust optical birefringence of NbOBr2. The ratio of the enhancement factor along the b- and c-axis of NbOBr2 reaches 2.43 and 5.27 for SHG and THG at 1500 nm pump, respectively, which leads to an extraordinarily high SHG anisotropic ratio of 17.82 and a 10° rotation of THG polarization. The research presents a feasible and practical strategy for developing high-efficiency and low-power-pumped on-chip nonlinear optical devices with tunable anisotropy.

Phonon-enhanced nonlinearities in hexagonal boron nitride.

Polar crystals can be driven into collective oscillations by optical fields tuned to precise resonance frequencies. As the amplitude of the excited phonon modes increases, novel processes scaling non-linearly with the applied fields begin to contribute to the dynamics of the atomic system. Here we show two such optical nonlinearities that are induced and enhanced by the strong phonon resonance in the van der Waals crystal hexagonal boron nitride (hBN). We predict and observe large sub-picosecond duration signals due to four-wave mixing (FWM) during resonant excitation. The resulting FWM signal allows for time-resolved observation of the crystal motion. In addition, we observe enhancements of third-harmonic generation with resonant pumping at the hBN transverse optical phonon. Phonon-induced nonlinear enhancements are also predicted to yield large increases in high-harmonic efficiencies beyond the third.

A two-dimensional mid-infrared optoelectronic retina enabling simultaneous perception and encoding.

Infrared machine vision system for object perception and recognition is becoming increasingly important in the Internet of Things era. However, the current system suffers from bulkiness and inefficiency as compared to the human retina with the intelligent and compact neural architecture. Here, we present a retina-inspired mid-infrared (MIR) optoelectronic device based on a two-dimensional (2D) heterostructure for simultaneous data perception and encoding. A single device can perceive the illumination intensity of a MIR stimulus signal, while encoding the intensity into a spike train based on a rate encoding algorithm for subsequent neuromorphic computing with the assistance of an all-optical excitation mechanism, a stochastic near-infrared (NIR) sampling terminal. The device features wide dynamic working range, high encoding precision, and flexible adaption ability to the MIR intensity. Moreover, an inference accuracy more than 96% to MIR MNIST data set encoded by the device is achieved using a trained spiking neural network (SNN).

Toward tunable band gap and tunable dirac point in bilayer graphene with molecular doping.

The bilayer graphene has attracted considerable attention for potential applications in future electronics and optoelectronics because of the feasibility to tune its band gap with a vertical displacement field to break the inversion symmetry. Surface chemical doping in bilayer graphene can induce an additional offset voltage to fundamentally affect the vertical displacement field and the band gap opening in bilayer graphene. In this study, we investigate the effect of chemical molecular doping on band gap opening in bilayer graphene devices with single or dual gate modulation. Chemical doping with benzyl viologen molecules modulates the displacement field to allow the opening of a transport band gap and the increase of the on/off ratio in the bilayer graphene transistors. Additionally, Fermi energy level in the opened gap can be rationally controlled by the amount of molecular doping to obtain bilayer graphene transistors with tunable Dirac points, which can be readily configured into functional devices, such as complementary inverters.

Small hysteresis nanocarbon-based integrated circuits on flexible and transparent plastic substrate.

We report small hysteresis integrated circuits by introducing monolayer graphene for the electrodes and a single-walled carbon nanotube network for the channel. Small hysteresis of the device originates from a defect-free graphene surface, where hysteresis was modulated by oxidation. This uniquely combined nanocarbon material device with transparent and flexible properties shows remarkable device performance; subthreshold voltage of 220 mV decade(-1), operation voltage of less than 5 V, on/off ratio of approximately 10(4), mobility of 81 cm(2) V(-1) s(-1), transparency of 83.8% including substrate, no significant transconductance changes in 1000 times of bending test, and only 36% resistance decrease at a tensile strain of 50%. Furthermore, because of the nearly Ohmic contact nature between the graphene and carbon nanotubes, this device demonstrated a contact resistance 100 times lower and a mobility 20 times higher, when compared to an Au electrode.

Infrared plasmons propagate through a hyperbolic nodal metal.

Metals are canonical plasmonic media at infrared and optical wavelengths, allowing one to guide and manipulate light at the nanoscale. A special form of optical waveguiding is afforded by highly anisotropic crystals revealing the opposite signs of the dielectric functions along orthogonal directions. These media are classified as hyperbolic and include crystalline insulators, semiconductors, and artificial metamaterials. Layered anisotropic metals are also anticipated to support hyperbolic waveguiding. However, this behavior remains elusive, primarily because interband losses arrest the propagation of infrared modes. Here, we report on the observation of propagating hyperbolic waves in a prototypical layered nodal-line semimetal ZrSiSe. The observed waveguiding originates from polaritonic hybridization between near-infrared light and nodal-line plasmons. Unique nodal electronic structures simultaneously suppress interband loss and boost the plasmonic response, ultimately enabling the propagation of infrared modes through the bulk of the crystal.