Theory of Photoluminescence Spectral Line Shapes of Semiconductor Nanocrystals.

Single-molecule photoluminescence (PL) spectroscopy of semiconductor nanocrystals (NCs) reveals the nature of exciton-phonon interactions in NCs. Understanding the homogeneous spectral line shapes and their temperature dependence remains an open problem. Here, we develop an atomistic model to describe the PL spectrum of NCs, accounting for excitonic effects, phonon dispersion relations, and exciton-phonon couplings. We validate our model using single-NC measurements on CdSe/CdS NCs from T = 4 to 290 K, and we find that the slightly asymmetric main peak at low temperatures is comprised of a narrow zero-phonon line (ZPL) and acoustic phonon sidebands. Furthermore, we identify the specific phonon modes that give rise to the optical phonon sidebands. At temperatures above 200 K, the spectral line width shows a stronger dependence upon the temperature, which we demonstrate to be correlated with higher order exciton-phonon couplings. We also identify the line width dependence upon reorganization energy, NC core sizes, and shell thicknesses.

Rationally Designed Eco-Friendly Solvent System for High-Performance, Large-Area Perovskite Solar Cells and Modules.

The important but remained issue to be addressed to achieve the mass production of perovskite solar modules include a large-area fabrication of high-quality perovskite film with eco-friendly, viable production methods. Although several efforts are made to achieve large-area fabrication of perovskite, the development of eco-friendly solvent system, which is precisely designed to be fit to scale-up methods are still challenging. Herein, this work develops the eco-friendly solvent/co-solvent system to produce a high-quality perovskite layer with a bathing in eco-friendly antisolvent. The new co-solvent/additive, methylsulfonylmethane (MSM), efficiently improves the overall solubility and has a suitable binding strength to the perovskite precursor, resulting in a high-quality perovskite film with antisolvent bathing method in large area. The resultant perovskite solar cells showed high power conversion efficiency of over 24% (in reverse scan), with a good long-term stability under continuous light illumination or damp-heat condition. MSM is also beneficial to produce a perovskite layer at low-temperature or high-humidity. MSM-based solvent system is finally applied to large-area, resulting in highly efficiency perovskite solar modules with PCE of 19.9% (by aperture) or 21.2% (by active area) in reverse scan. These findings contribute to step forward to a mass production of perovskite solar modules with eco-friendly way.

Narrow Intrinsic Line Widths and Electron-Phonon Coupling of InP Colloidal Quantum Dots.

InP quantum dots (QDs) are the material of choice for QD display applications and have been used as active layers in QD light-emitting diodes (QDLEDs) with high efficiency and color purity. Optimizing the color purity of QDs requires understanding mechanisms of spectral broadening. While ensemble-level broadening can be minimized by synthetic tuning to yield monodisperse QD sizes, single QD line widths are broadened by exciton-phonon scattering and fine-structure splitting. Here, using photon-correlation Fourier spectroscopy, we extract average single QD line widths of 50 meV at 293 K for red-emitting InP/ZnSe/ZnS QDs, among the narrowest for colloidal QDs. We measure InP/ZnSe/ZnS single QD emission line shapes at temperatures between 4 and 293 K and model the spectra using a modified independent boson model. We find that inelastic acoustic phonon scattering and fine-structure splitting are the most prominent broadening mechanisms at low temperatures, whereas pure dephasing from elastic acoustic phonon scattering is the primary broadening mechanism at elevated temperatures, and optical phonon scattering contributes minimally across all temperatures. Conversely for CdSe/CdS/ZnS QDs, we find that optical phonon scattering is a larger contributor to the line shape at elevated temperatures, leading to intrinsically broader single-dot line widths than for InP/ZnSe/ZnS. We are able to reconcile narrow low-temperature line widths and broad room-temperature line widths within a self-consistent model that enables parametrization of line width broadening, for different material classes. This can be used for the rational design of more spectrally narrow materials. Our findings reveal that red-emitting InP/ZnSe/ZnS QDs have intrinsically narrower line widths than typically synthesized CdSe QDs, suggesting that these materials could be used to realize QDLEDs with high color purity.

Interfacial Trap-Assisted Triplet Generation in Lead Halide Perovskite Sensitized Solid-State Upconversion.

Photon upconversion via triplet-triplet annihilation (TTA) has promise for overcoming the Shockley-Queisser limit for single-junction solar cells by allowing the utilization of sub-bandgap photons. Recently, bulk perovskites have been employed as sensitizers in solid-state upconversion devices to circumvent poor exciton diffusion in previous nanocrystal (NC)-sensitized devices. However, an in-depth understanding of the underlying photophysics of perovskite-sensitized triplet generation is still lacking due to the difficulty of precisely controlling interfacial properties of fully solution-processed devices. In this study, interfacial properties of upconversion devices are adjusted by a mild surface solvent treatment, specifically altering perovskite surface properties without perturbing the bulk perovskite. Thermal evaporation of the annihilator precludes further solvent contamination. Counterintuitively, devices with more interfacial traps show brighter upconversion. Approximately an order of magnitude difference in upconversion brightness is observed across different interfacial solvent treatments. Sequential charge transfer and interfacial trap-assisted triplet sensitization are demonstrated by comparing upconversion performance, transient photoluminescence dynamics, and magnetic field dependence of the devices. Incomplete triplet conversion from transferred charges and consequent triplet-charge annihilation (TCA) are also observed. The observations highlight the importance of interfacial control and provide guidance for further design and optimization of upconversion devices using perovskites or other semiconductors as sensitizers.

Continuous External Tissue Expansion Closure Technique for Management of Forearm Compartment Syndrome Releases and Simple Upper-Extremity Wounds.

Upper-extremity wounds from various etiologies such as trauma and fasciotomies can prove to be problematic for the upper-extremity surgeon. These defects can result in considerable morbidity often requiring prolonged wound care and the eventual use of skin grafting from a separate painful donor site. Tissue expansion takes advantage of the viscoelastic properties of skin to provide additional tissue for reconstruction. The authors present a technique using a continuous external tissue expansion device for closure of upper-extremity wounds.

Efficient perovskite solar cells via improved carrier management.

Metal halide perovskite solar cells (PSCs) are an emerging photovoltaic technology with the potential to disrupt the mature silicon solar cell market. Great improvements in device performance over the past few years, thanks to the development of fabrication protocols1-3, chemical compositions4,5 and phase stabilization methods6-10, have made PSCs one of the most efficient and low-cost solution-processable photovoltaic technologies. However, the light-harvesting performance of these devices is still limited by excessive charge carrier recombination. Despite much effort, the performance of the best-performing PSCs is capped by relatively low fill factors and high open-circuit voltage deficits (the radiative open-circuit voltage limit minus the high open-circuit voltage)11. Improvements in charge carrier management, which is closely tied to the fill factor and the open-circuit voltage, thus provide a path towards increasing the device performance of PSCs, and reaching their theoretical efficiency limit12. Here we report a holistic approach to improving the performance of PSCs through enhanced charge carrier management. First, we develop an electron transport layer with an ideal film coverage, thickness and composition by tuning the chemical bath deposition of tin dioxide (SnO2). Second, we decouple the passivation strategy between the bulk and the interface, leading to improved properties, while minimizing the bandgap penalty. In forward bias, our devices exhibit an electroluminescence external quantum efficiency of up to 17.2 per cent and an electroluminescence energy conversion efficiency of up to 21.6 per cent. As solar cells, they achieve a certified power conversion efficiency of 25.2 per cent, corresponding to 80.5 per cent of the thermodynamic limit of its bandgap.

The Oculocardiac Reflex: Its Evolution and Management.

INTRODUCTION: The oculocardiac reflex is initiated by a pressure stimulus to the orbit or periorbital structures causing in bradycardia transmitted via the trigeminal-vagus nerve reflex arc. While this most frequently occurs with ophthalmologic surgeries, trauma to the orbit and periorbital structures can result in bradycardia and even in some cases, asystole. The aim of this case report and review of the literature is to identify and examine recent studies of the oculocardiac reflex related to facial trauma and to identify associated patient age, symptoms, and fracture patterns. METHODS: A literature search was performed using the database within PubMed.gov using the term "oculocardiac." Results were reviewed for case reports or series related to facial trauma from the year 2000 to 2019. Studies were then evaluated for fracture pattern, presence of entrapment, patient symptoms, and age. RESULTS: The initial search resulted in 109 articles. A total of 22 articles were case reports or series of trauma patients. Twenty articles met inclusion criteria. Median age was 22 years. Eleven patients sustained orbital floor fractures. Four patients sustained medial wall fractures. Three patients had concomitant orbital floor and zygomatic fractures, and 4 with concomitant orbital floor and medial wall fractures. The most common extracardiac symptom experienced was nausea and vomiting (15/23) followed by diplopia (10/23). Status of entrapment was available in 20 patients of which entrapment was reported in fourteen (14/20). CLINICAL REPORT: A 26-year old male presents after blunt trauma to the face resulting in a left orbital floor, rim, and maxillary fractures. Extraocular movements were initially intact and the patient had no diplopia. He developed bradycardia to 30 to 40 bpm just prior to induction of anesthesia. He was found to have developed entrapment of the inferior rectus muscle. The orbital floor and rim were repaired with complete resolution of bradycardia. CONCLUSION: Patients who sustain maxillofacial trauma involving the orbit are at risk of developing the oculocardiac reflex. Patients tend to be younger. The orbital floor is more commonly the site of traumatic injury. Nausea and vomiting are common encountered symptoms. The oculocardiac reflex, clinicians must recognize, is not static but may evolve over a patient's clinical course as seen in our patient.

Can we increase detection? A nationwide analysis of age-related fractures in child abuse.

PURPOSE: The purpose of this study was to stratify fractures associated with child abuse in relation to the child's age. METHODS: The Kids' Inpatient Database (1997-2012) was queried for all patients (<18 years old) with a diagnosis of fracture and child abuse. The primary outcome was age-related determinants of fracture distribution. Chi-squared analysis was used for statistical analysis where appropriate, with significance set at p < 0.05. RESULTS: More than 39,000 children were admitted for child abuse, and 26% sustained fractures. Most were infants (median age 0 year [IQR 0-1]). 28% sustained multiple fractures, and 27% had skull fractures. By age, infants had the highest rate of multiple fractures (33% vs 16% 1-4 years), and the highest rate of closed skull fractures (33% vs 21% ages 1-4), while adolescents had more facial fractures (43% vs 11% ages 9-12), all p < 0.001. Multiple rib fractures were more commonly seen in infants (28% vs 8% ages 1-4), while children 5-8 years had the highest rates of clavicular fractures (7% vs 3% in infants), all p < 0.001. CONCLUSION: Age-related fracture patterns exist and may be due to changing mechanism of abuse as a child grows. These age-related fracture patterns can help aid in healthcare detection of child abuse in hopes to thwart further abuse. TYPE OF STUDY: Retrospective comparative study. LEVEL OF EVIDENCE: Level III.

Author Correction: How machine learning can help select capping layers to suppress perovskite degradation.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

How machine learning can help select capping layers to suppress perovskite degradation.

Environmental stability of perovskite solar cells (PSCs) has been improved by trial-and-error exploration of thin low-dimensional (LD) perovskite deposited on top of the perovskite absorber, called the capping layer. In this study, a machine-learning framework is presented to optimize this layer. We featurize 21 organic halide salts, apply them as capping layers onto methylammonium lead iodide (MAPbI3) films, age them under accelerated conditions, and determine features governing stability using supervised machine learning and Shapley values. We find that organic molecules' low number of hydrogen-bonding donors and small topological polar surface area correlate with increased MAPbI3 film stability. The top performing organic halide, phenyltriethylammonium iodide (PTEAI), successfully extends the MAPbI3 stability lifetime by 4 ± 2 times over bare MAPbI3 and 1.3 ± 0.3 times over state-of-the-art octylammonium bromide (OABr). Through characterization, we find that this capping layer stabilizes the photoactive layer by changing the surface chemistry and suppressing methylammonium loss.

Accidental Magnetic Resonance Imaging Activation of Carbon Dioxide Tissue Expanders.

Implant-based reconstruction is the most common form of breast reconstruction following mastectomy. It is most often performed in 2 stages using saline-based tissue expanders, which are then exchanged for permanent implants. Serial expansions are performed by accessing a port in the office, an inconvenient and sometimes painful process. A carbon dioxide tissue expander is a device that provides a needle-free, patient-controlled expansion utilizing a remote-controlled CO2 canister. While a patient-controlled expansion offers convenience, given that the CO2 reservoir holds approximately 1500 mL of gas, the potential for malfunction resulting in an uncontrolled expansion in unique to this device. The authors present a case report of a patient with bilateral pre-pectoral tissue expanders who underwent magnetic resonance imaging, resulting in uncontrolled expansion.

Treatment of Rhinophyma With Surgical Excision and Amniotic Membrane.

Rhinophyma is a phenotypic subtype of rosacea affecting the nose. It is characterized by phymatous changes, skin thickening/fibrosis, glandular hyperplasia, and chronic inflammation. Treatment of severe rhinophyma is predominantly surgical excision with closure by secondary intention. Amniotic membrane has been used to promote wound healing, fibrosis, and inflammation. In this case study, the authors present a 63-year-old male with longstanding rhinophyma treated with surgical excision with intraoperative placement of amniotic membrane.

Zinc Thiolate Enables Bright Cu-Deficient Cu-In-S/ZnS Quantum Dots.

Copper indium sulfide (CIS) colloidal quantum dots (QDs) are a promising candidate for commercially viable QD-based optical applications, for example as colloidal photocatalysts or in luminescent solar concentrators (LSCs). CIS QDs with good photoluminescence quantum yields (PLQYs) and tunable emission wavelength via size and composition control are previously reported. However, developing an understanding and control over the growth of electronically passivating inorganic shells would enable further improvements of the photophysical properties of CIS QDs. To improve the optical properties of CIS QDs, the focus is on the growth of inorganic shells via the popular metal-carboxylate/alkane thiol decomposition reaction. 1) The role of Zn-carboxylate and Zn-thiolate on the formation of ZnS shells on Cu-deficient CIS (CDCIS) QDs is studied, 2) this knowledge is leveraged to yield >90% PLQY CDCIS/ZnS core/shell QDs, and 3) a mechanism for ZnS shells grown from zinc-carboxylate/alkane thiol decomposition is proposed.

Alternative Therapies to Fat Grafting in the Craniofacial Region.

Autologous fat grafting is a technique with various applications in the craniofacial region ranging from the treatment of wounds, scars, keloids, and soft tissue deformities. In this review, alternative therapies to fat grafting are discussed. These are composed of established therapies like silicone gel or sheeting, corticosteroids, cryotherapy, and laser therapy. Novel applications of negative pressure wound therapy, botulinum toxin A injection, and biologic agents are also reviewed.

Single Nanocrystal Spectroscopy of Shortwave Infrared Emitters.

Short-wave infrared (SWIR) emitters are at the center of ground-breaking applications in biomedical imaging, next-generation optoelectronic devices, and optical communications. Colloidal nanocrystals based on indium arsenide are some of the most promising SWIR emitters to date. However, the lack of single-particle spectroscopic methods accessible in the SWIR has prevented advances in both nanocrystal synthesis and fundamental characterization of emitters. Here, we demonstrate an implementation of a solution photon correlation Fourier spectroscopy (s-PCFS) experiment utilizing the SWIR sensitivity and time resolution of superconducting nanowire single-photon detectors to extract single-particle emission linewidths from colloidal indium arsenide/cadmium selenide (InAs/CdSe) core/shell nanocrystals emissive from 1.2 to 1.6 µm. We show that the average single InAs/CdSe nanocrystal fluorescence linewidth is, remarkably, as narrow as 52 meV, similar to what has been observed in some of the most narrowband nanostructured emitters in the visible region. Additionally, the single nanocrystal fluorescence linewidth increases with increasing shell thickness, suggesting exciton-phonon coupling as the dominant emission line-broadening mechanism in this system. The development of the SWIR s-PCFS technique has enabled measurements of spectral linewidths of colloidal SWIR-emissive NCs in solution and provides a platform to study the single NC spectral characteristics of SWIR emitters.

Increasing the Collision Rate of Particle Impact Electroanalysis with Magnetically Guided Pt-Decorated Iron Oxide Nanoparticles.

An integrated microfluidic/magnetophoretic methodology was developed for improving signal response time and detection limits for the chronoamperometric observation of discrete nanoparticle/electrode interactions by electrocatalytic amplification. The strategy relied on Pt-decorated iron oxide nanoparticles which exhibit both superparamagnetism and electrocatalytic activity for the oxidation of hydrazine. A wet chemical synthetic approach succeeded in the controlled growth of Pt on the surface of FeO/Fe3O4 core/shell nanocubes, resulting in highly uniform Pt-decorated iron oxide hybrid nanoparticles with good dispersibility in water. The unique mechanism of hybrid nanoparticle formation was investigated by electron microscopy and spectroscopic analysis of isolated nanoparticle intermediates and final products. Discrete hybrid nanoparticle collision events were detected in the presence of hydrazine, an electrochemical indicator probe, using a gold microband electrode integrated into a microfluidic channel. In contrast with related systems, the experimental nanoparticle/electrode collision rate correlates more closely with simple theoretical approximations, primarily due to the accuracy of the nanoparticle tracking analysis method used to quantify nanoparticle concentrations and diffusion coefficients. Further modification of the microfluidic device was made by applying a tightly focused magnetic field to the detection volume to attract the magnetic nanoprobes to the microband working electrode, thereby resulting in a 6-fold increase to the relative frequency of chronoamperometric signals corresponding to discrete nanoparticle impact events.

Direct electrochemical detection of individual collisions between magnetic microbead/silver nanoparticle conjugates and a magnetized ultramicroelectrode.

Here, we report on the electrochemical detection of individual collisions between a conjugate consisting of silver nanoparticles (AgNPs) linked to conductive magnetic microbeads (cMµBs) via DNA hybridization and a magnetized electrode. The important result is that the presence of the magnetic field increases the flux of the conjugate to the electrode surface, and this in turn increases the collision frequency and improves the limit of detection (20 aM). In addition, the magnitude of the charge associated with the collisions is greatly enhanced in the presence of the magnetic field. The integration of DNA into the detection protocol potentially provides a means for using electrochemical collisions for applications in biological and chemical sensing.

Electrochemical detection of insulating beads at subattomolar concentration via magnetic enrichment in a microfluidic device.

We report electrochemical detection of collisions between individual magnetic microbeads, present at subattomolar concentrations, and electrode surfaces. This limit of detection is 4 orders of magnitude lower than has been reported previously, and it is enabled by using a magnetic field to preconcentrate the microbeads prior to detection in a microfluidic electrochemical cell. Importantly, the frequency of collisions between the microbeads and the electrode is not compromised by the low concentration of microbeads. These findings represent an unusual case of detecting individual electrochemical events at very low analyte concentration. In addition to experiments supporting these claims, finite-element simulations provide additional insights into the nature of the interactions between flowing microbeads and their influence on electrochemical processes.