75 research outputs found
Defect-induced modification of low-lying excitons and valley selectivity in monolayer transition metal dichalcogenides
We study the effect of point-defect chalcogen vacancies on the optical
properties of monolayer transition metal dichalcogenides using ab initio GW and
Bethe-Salpeter equation calculations. We find that chalcogen vacancies
introduce unoccupied in-gap states and occupied resonant defect states within
the quasiparticle continuum of the valence band. These defect states give rise
to a number of strongly-bound defect excitons and hybridize with excitons of
the pristine system, reducing the valley-selective circular dichroism. Our
results suggest a pathway to tune spin-valley polarization and other optical
properties through defect engineering
Identifying substitutional oxygen as a prolific point defect in monolayer transition metal dichalcogenides with experiment and theory
Chalcogen vacancies are considered to be the most abundant point defects in
two-dimensional (2D) transition-metal dichalcogenide (TMD) semiconductors, and
predicted to result in deep in-gap states (IGS). As a result, important
features in the optical response of 2D-TMDs have typically been attributed to
chalcogen vacancies, with indirect support from Transmission Electron
Microscopy (TEM) and Scanning Tunneling Microscopy (STM) images. However, TEM
imaging measurements do not provide direct access to the electronic structure
of individual defects; and while Scanning Tunneling Spectroscopy (STS) is a
direct probe of local electronic structure, the interpretation of the chemical
nature of atomically-resolved STM images of point defects in 2D-TMDs can be
ambiguous. As a result, the assignment of point defects as vacancies or
substitutional atoms of different kinds in 2D-TMDs, and their influence on
their electronic properties, has been inconsistent and lacks consensus. Here,
we combine low-temperature non-contact atomic force microscopy (nc-AFM), STS,
and state-of-the-art ab initio density functional theory (DFT) and GW
calculations to determine both the structure and electronic properties of the
most abundant individual chalcogen-site defects common to 2D-TMDs.
Surprisingly, we observe no IGS for any of the chalcogen defects probed. Our
results and analysis strongly suggest that the common chalcogen defects in our
2D-TMDs, prepared and measured in standard environments, are substitutional
oxygen rather than vacancies
Diaphragm plication following phrenic nerve injury: a comparison of paediatric and adult patients
Background: A study was undertaken to evaluate whether adults differ from children in the indications and outcome of diaphragmatic plication following phrenic nerve injury. Methods: A retrospective study was performed of 21 patients, 10 below the age of 5 and 11 older than 37 years. The indication for surgery for all the children was failure to wean from ventilatory support. The indications for surgery in the adult group were ventilator dependency (n=4) and symptomatic dyspnoea (n=7). All patients had at least one imaging study confirming diaphragmatic paralysis. The American Thoracic Society (ATS) dyspnoea scale, pulmonary function tests, and quantitative pulmonary perfusion scans were used as evaluation parameters. At surgery the diaphragm was centrally plicated. Results: One child died immediately after surgery due to irreversible heart failure and two children died within 2 months of surgery from ongoing complications of their original condition. These three patients were considered as selection failures. Seven children were weaned from ventilatory support within a median of 4 days (range 2–140). Only one of four ventilated adults was successfully weaned. Seven adults who underwent surgery for chronic symptoms had a marked subjective improvement of 2–3 levels in the ATS dyspnoea scale. Pulmonary function studies in the seven symptomatic adults showed a 40% improvement above baseline. Severely asymmetrical perfusion scans reverted to a normal pattern after plication. Conclusions: Diaphragmatic plication offers a significant benefit to children with diaphragmatic paralysis and should be performed early to facilitate weaning from mechanical ventilation. While plication is of limited benefit in weaning ventilated adults, it results in significant subjective and objective lifetime improvement in non-ventilated symptomatic adults
Ultrasound-guided serratus anterior plane block for analgesia after thoracic surgery
Michael Semyonov,1,* Ekaterina Fedorina,1,* Julia Grinshpun,2 Michael Dubilet,1 Yael Refaely,3 Leonid Ruderman,3 Leonid Koyfman,1 Michael Friger,2 Alexander Zlotnik,1 Moti Klein,1 Evgeni Brotfain1 1Department of Anesthesiology and Critical Care, General Intensive Care Unit, Soroka Medical Center, Ben-Gurion University of the Negev, Beer Sheva, Israel; 2Department of Public Health, Faculty of Health Sciences, Ben-Gurion University of the Negev, Beer Sheva, Israel; 3Department of Cardiothoracic Surgery, Soroka Medical Center, Ben‑Gurion University of the Negev, Beer Sheva, Israel *These authors contributed equally to this work Background: Patients who undergo surgical procedures that impair the integrity of the chest wall frequently experience extremely severe postoperative pain. Opiates and weaker analgesics, such as nonsteroidal anti-inflammatory drugs (NSAIDs), are not sufficiently effective in achieving control of severe pain and might cause respiratory and gastrointestinal complications. In the past decade, there has been an increased interest in the use of regional nerve blocks for post-thoracoscopy and post-thoracotomy analgesia. Methods: This is a prospective, randomized, double-blind and single-center study. We recruited 104 patients who underwent elective thoracoscopy. Prior to surgery, the participating patients were randomized into one of two study groups: Group 1- the “standard control group” that received standard postoperative pain control with intravenous opioids, NSAIDs and acetaminophen (paracetamol) and Group 2- the “block group” that was treated by ultrasound-guided serratus anterior plane (SAP) block (a single injection of 0.25% bupivacaine hydrochloride 2 mg/kg plus dexamethasone 8 mg) with standard postoperative pain control regimen. We compared the clinical, laboratory, and postoperative pain assessment data of both groups. Results: Patients in the SAP block Group 2 reported significantly lower levels of pain after thoracic surgery as assessed by their visual analog scale scores, as compared to the patients in the standard pain control Group 1 (P<0.001). The total dosage of morphine and tramadol required for pain relief during the first hours after surgery was significantly lower in the patients who received SAP block. Also, the incidence of vomiting after surgery was significantly lower among the patients who received SAP block than among the patients who received standard pain control. Conclusion: The results of the present study suggest that SAP block is an effective adjuvant treatment option for post-thoracic surgery analgesia. Compared to the current methods used for post-thoracic surgery pain relief, SAP block has some significant merits, particularly its ease of use and its low potential for side effects. Keywords: serratus anterior plane block, thoracic surgery, thoracoscopy, post-thoracic surgery pain relief, ultrasound-guided regional anesthesia, post-thoracotomy analgesi
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