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.

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.

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).

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.

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.

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.

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.

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.

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.

Clinical outcome of ultrasound-guided atelocollagen injection for patients with partial rotator cuff tear in an outpatient clinic: a preliminary study.

BACKGROUND: Atelocollagen has been studied for restoration of rotator cuff tendon. In this study, we attempted to evaluate the clinical outcome of ultrasound-guided atelocollagen injection in an outpatient clinic for patients with partial rotator cuff tear. METHODS: We recruited 42 outpatients who visited our hospital from May 2019 to September 2019. Atelocollagen injection was performed in patients with partial rotator cuff tear diagnosed by magnetic resonance imaging and ultrasound. American Shoulder and Elbow Surgeons (ASES), Constant, Korean Shoulder Score (KSS) and Simple Shoulder Test (SST) scores, and range of motion were assessed before injection and after 2 months. Statistically, we analyzed the clinical results using the Wilcoxon signed-rank test. RESULTS: Finally, 15 patients were enrolled for analysis. There was no significant difference between pre- and post-injection in terms of range of motion, ASES (57.0 vs. 60.4), Constant (56.4 vs. 58.9), KSS (64.6 vs. 68.5), and pain-visual analog scale (4.2 vs. 3.7), except function-visual analog scale (F-VAS; 6.3 vs. 7.1) and SST (6.6 vs. 6.9). A significant difference was found in SST (P=0.046) and F-VAS (P=0.009). According to the ultrasound results at 2 months, we found hyperechoic materials in three of seven patients. The most common complication of atelocollagen injection was post-injection pain (53%, 8/15). CONCLUSIONS: Ultrasound-guided atelocollagen injection for partial rotator cuff tear showed no significant change in terms of clinical outcomes, except for F-vas and SST score. Tendon regeneration was not clear due to the remnants of atelocollagen present at 2-month follow-up ultrasound. There seems to be alarming post-injection pain for 2 to 3 days in the patients who received atelocollagen injection in an outpatient clinic.

Hidden Long Head of the Biceps Tendon Instability and Concealed Intratendinous Subscapularis Tears.

BACKGROUND: Few studies have described the characteristics of a concealed intratendinous subscapularis tear (CIST), and there is a lack of research on the preoperative predictability of such lesions. PURPOSE: To describe the characteristics of a CIST as seen on magnetic resonance imaging (MRI) and intraoperatively and to develop a scoring system for predicting such lesions. STUDY DESIGN: Case series; Level of evidence, 4. METHODS: Retrospectively, we identified 43 patients with CISTs among 442 consecutive patients who had undergone rotator cuff repair from July 2014 to June 2016. Range of motion, visual analog scale results for pain and function, and patient-reported outcome scores were evaluated preoperatively and at 1 and 2 years postoperatively. CISTs were classified arthroscopically as small (<5 mm), medium (5-10 mm), and large (>10 mm). We performed repair (≥50%) or debridement (<50%) depending on the total subscapularis tendon tear size including the CIST. Preoperative MRI findings were analyzed by 2 observers and were correlated with the arthroscopic findings. A 10-point scoring system was developed based on characteristics during the physical examination (anterior tenderness, bear hug sign), MRI (biceps tendon displacement and subluxation, subscapularis signal change just lateral to the lesser tuberosity), and arthroscopic surgery (medial biceps tendon lesion, combined subscapularis tendon tear), with a cutoff value of ≥7 predicting a CIST. After the retrospective study, we prospectively enrolled 95 patients to validate the 10-point CIST scoring system. RESULTS: All 43 patients diagnosed with a CIST during the retrospective study improved both range of motion and functional scores at 1 year postoperatively. The interrater agreement of the 2 observers was substantial for the evaluation of all parameters except for subscapularis tear classification, which was moderate. On arthroscopic surgery, 11 small, 19 medium, and 13 large CISTs were detected. The preliminary prospective study showed a sensitivity of 61.9%, specificity of 94.3%, positive predictive value of 89.0%, negative predictive value of 75.7%, and accuracy of 80.0% when the cutoff value was set at ≥7 on the CIST scoring system. CONCLUSION: A CIST can be suspected using a combination of preoperative MRI and intra-articular diagnostic arthroscopic findings, but a definitive diagnosis requires an arthroscopic view. On the 10-point CIST scoring system, a score of ≥5 can be suggestive of a CIST, and a score of ≥7 is most likely to predict a CIST.

Development and Clinical Evaluation of a Web-Based Upper Limb Home Rehabilitation System Using a Smartwatch and Machine Learning Model for Chronic Stroke Survivors: Prospective Comparative Study.

BACKGROUND: Recent advancements in wearable sensor technology have shown the feasibility of remote physical therapy at home. In particular, the current COVID-19 pandemic has revealed the need and opportunity of internet-based wearable technology in future health care systems. Previous research has shown the feasibility of human activity recognition technologies for monitoring rehabilitation activities in home environments; however, few comprehensive studies ranging from development to clinical evaluation exist. OBJECTIVE: This study aimed to (1) develop a home-based rehabilitation (HBR) system that can recognize and record the type and frequency of rehabilitation exercises conducted by the user using a smartwatch and smartphone app equipped with a machine learning (ML) algorithm and (2) evaluate the efficacy of the home-based rehabilitation system through a prospective comparative study with chronic stroke survivors. METHODS: The HBR system involves an off-the-shelf smartwatch, a smartphone, and custom-developed apps. A convolutional neural network was used to train the ML algorithm for detecting home exercises. To determine the most accurate way for detecting the type of home exercise, we compared accuracy results with the data sets of personal or total data and accelerometer, gyroscope, or accelerometer combined with gyroscope data. From March 2018 to February 2019, we conducted a clinical study with two groups of stroke survivors. In total, 17 and 6 participants were enrolled for statistical analysis in the HBR group and control group, respectively. To measure clinical outcomes, we performed the Wolf Motor Function Test (WMFT), Fugl-Meyer Assessment of Upper Extremity, grip power test, Beck Depression Inventory, and range of motion (ROM) assessment of the shoulder joint at 0, 6, and 12 months, and at a follow-up assessment 6 weeks after retrieving the HBR system. RESULTS: The ML model created with personal data involving accelerometer combined with gyroscope data (5590/5601, 99.80%) was the most accurate compared with accelerometer (5496/5601, 98.13%) or gyroscope data (5381/5601, 96.07%). In the comparative study, the drop-out rates in the control and HBR groups were 40% (4/10) and 22% (5/22) at 12 weeks and 100% (10/10) and 45% (10/22) at 18 weeks, respectively. The HBR group (n=17) showed a significant improvement in the mean WMFT score (P=.02) and ROM of flexion (P=.004) and internal rotation (P=.001). The control group (n=6) showed a significant change only in shoulder internal rotation (P=.03). CONCLUSIONS: This study found that a home care system using a commercial smartwatch and ML model can facilitate participation in home training and improve the functional score of the WMFT and shoulder ROM of flexion and internal rotation in the treatment of patients with chronic stroke. This strategy can possibly be a cost-effective tool for the home care treatment of stroke survivors in the future. TRIAL REGISTRATION: Clinical Research Information Service KCT0004818; https://tinyurl.com/y92w978t.

Disassembling 2D van der Waals crystals into macroscopic monolayers and reassembling into artificial lattices.

Two-dimensional materials from layered van der Waals (vdW) crystals hold great promise for electronic, optoelectronic, and quantum devices, but technological implementation will be hampered by the lack of high-throughput techniques for exfoliating single-crystal monolayers with sufficient size and high quality. Here, we report a facile method to disassemble vdW single crystals layer by layer into monolayers with near-unity yield and with dimensions limited only by bulk crystal sizes. The macroscopic monolayers are comparable in quality to microscopic monolayers from conventional Scotch tape exfoliation. The monolayers can be assembled into macroscopic artificial structures, including transition metal dichalcogenide multilayers with broken inversion symmetry and substantially enhanced nonlinear optical response. This approach takes us one step closer to mass production of macroscopic monolayers and bulk-like artificial materials with controllable properties.

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.

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.

Sorting centimetre-long single-walled carbon nanotubes.

While several approaches have been developed for sorting metallic (m) or semiconducting (s) single-walled carbon nanotubes (SWCNTs), the length of SWCNTs is limited within a micrometer, which restricts excellent electrical performances of SWCNTs for macro-scale applications. Here, we demonstrate a simple sorting method of centimetre-long aligned m- and s-SWCNTs. Ni particles were selectively and uniformly coated along the 1-cm-long m-SWCNTs by applying positive gate bias during electrochemical deposition with continuous electrolyte injection. To sort s-SWCNTs, the Ni coating was oxidized to form insulator outer for blocking of current flow through inner m-SWCNTs. Sorting of m-SWCNTs were demonstrated by selective etching of s-SWCNTs via oxygen plasma, while the protected m-SWCNTs by Ni coating remained intact. The series of source-drain pairs were patterned along the 1-cm-long sorted SWCNTs, which confirmed high on/off ratio of 10(4)-10(8) for s-SWCNTs and nearly 1 for m-SWCNTs.

Oxidation Effect in Octahedral Hafnium Disulfide Thin Film.

Atomically smooth van der Waals materials are structurally stable in a monolayer and a few layers but are susceptible to oxygen-rich environments. In particular, recently emerging materials such as black phosphorus and perovskite have revealed stronger environmental sensitivity than other two-dimensional layered materials, often obscuring the interesting intrinsic electronic and optical properties. Unleashing the true potential of these materials requires oxidation-free sample preparation that protects thin flakes from air exposure. Here, we fabricated few-layer hafnium disulfide (HfS2) field effect transistors (FETs) using an integrated vacuum cluster system and study their electronic properties and stability under ambient conditions. By performing all the device fabrication and characterization procedure under an oxygen- and moisture-free environment, we found that few-layer AA-stacking HfS2-FETs display excellent field effect responses (Ion/Ioff ≈ 10(7)) with reduced hysteresis compared to the FETs prepared under ambient conditions. Oxidation of HfS2 occurs uniformly over the entire area, increasing the film thickness by 250% at a prolonged oxidation time of >120 h, while defects on the surface are the preferential initial oxidation sites. We further demonstrated that the stability of the device in air is significantly improved by passivating FETs with BN in a vacuum cluster.

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.