Transformation of K2Sb8Q13 and KSb5Q8 Bulk Crystals to Sb2Q3 (Q = S, Se) Nanofibers by Acid-Base Solution Chemistry

The ability to manipulate crystal structures using kinetic control is of broad interest because it enables the design of materials with structures, compositions, and morphologies that may otherwise be unattainable. Herein, we report the low-temperature structural transformation of bulk inorganic crystals driven by hard-soft acid-base (HSAB) chemistry. We show that the three-dimensional framework K₂Sb₈Q₁₃ and layered KSb₅Q₈ (Q = S, Se, and Se/S solid solutions) compounds transform to one-dimensional Sb₂Q₃ nano/microfibers in N₂H₄·H₂O solution by releasing Q^2- and K⁺ ions. At 100 °C and ambient pressure, a transformation process takes place that leads to significant structural changes in the materials, including the formation and breakage of covalent bonds between Sb and Q. Despite the insolubility of the starting crystals in N₂H₄·H₂O under the given conditions, the mechanism of this transformation can be rationalized by applying the HSAB principle. By adjusting factors such as the reactants' acid/base properties, temperature, and pressure, the process can be controlled, allowing for the achievement of a wide range of optical band gaps (ranging from 1.14 to 1.59 eV) while maintaining the solid solution nature of the anion sublattice in the Sb₂Q₃ nanofibers.

Plainly fixing crystal lattices

A thermoelectric alloy achieves high performance in electronic cooling.

Electronic Structure Manipulation of the Mott Insulator RuCl3 via Single-Crystal to Single-Crystal Topotactic Transformation

The core task for Mott insulators includes how rigid distributions of electrons evolve and how these induce exotic physical phenomena. However, it is highly challenging to chemically dope Mott insulators to tune properties. Herein, we report how to tailor electronic structures of the honeycomb Mott insulator RuCl₃ employing a facile and reversible single-crystal to single-crystal intercalation process. The resulting product (NH₄ )_0.5 RuCl₃ ⋅1.5 H₂ O forms a new hybrid superlattice of alternating RuCl₃ monolayers with NH₄ ⁺ and H₂ O molecules. Its manipulated electronic structure markedly shrinks the Mott-Hubbard gap from 1.2 to 0.7 eV. Its electrical conductivity increases by more than 10³ folds. This arises from concurrently enhanced carrier concentration and mobility in contrary to the general physics rule of their inverse proportionality. We show topotactic and topochemical intercalation chemistry to control Mott insulators, escalating the prospect of discovering exotic physical phenomena.

Atomic Level Defect Structure Engineering for Unusually High Average Thermoelectric Figure of Merit in n-Type PbSe Rivalling PbTe

Realizing high average thermoelectric figure of merit (ZT_ave ) and power factor (PF_ave ) has been the utmost task in thermoelectrics. Here the new strategy to independently improve constituent factors in ZT is reported, giving exceptionally high ZT_ave and PF_ave in n-type PbSe. The nonstoichiometric, alloyed composition and resulting defect structures in new Pb_{1+ x} Se_0.8 Te_0.2 (x = 0-0.125) system is key to this achievement. First, incorporating excess Pb unusually increases carrier mobility (µ_H ) and concentration (n_H ) simultaneously in contrast to the general physics rule, thereby raising electrical conductivity (σ). Second, modifying charge scattering mechanism by the authors' synthesis process boosts a magnitude of Seebeck coefficient (S) above theoretical expectations. Detouring the innate inverse proportionality between n_H and µ_H ; and σ and S enables independent control over them and change the typical trend of PF to temperature, giving remarkably high PF_ave ≈20 µW cm^-1 K^-2 from 300 to 823 K. The dual incorporation of Te and excess Pb generates unusual antisite Pb at the anionic site and displaced Pb from the ideal position, consequently suppressing lattice thermal conductivity. The best composition exhibits a ZT_ave of ≈1.2 from 400 to 823 K, one of the highest reported for all n-type PbQ (Q = chalcogens) materials.

Evaluation of prognostic risk models for postoperative pulmonary complications in adult patients undergoing major abdominal surgery: a systematic review and international external validation cohort study

BACKGROUND

Stratifying risk of postoperative pulmonary complications after major abdominal surgery allows clinicians to modify risk through targeted interventions and enhanced monitoring. In this study, we aimed to identify and validate prognostic models against a new consensus definition of postoperative pulmonary complications.

METHODS

We did a systematic review and international external validation cohort study. The systematic review was done in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. We searched MEDLINE and Embase on March 1, 2020, for articles published in English that reported on risk prediction models for postoperative pulmonary complications following abdominal surgery. External validation of existing models was done within a prospective international cohort study of adult patients (≥18 years) undergoing major abdominal surgery. Data were collected between Jan 1, 2019, and April 30, 2019, in the UK, Ireland, and Australia. Discriminative ability and prognostic accuracy summary statistics were compared between models for the 30-day postoperative pulmonary complication rate as defined by the Standardised Endpoints in Perioperative Medicine Core Outcome Measures in Perioperative and Anaesthetic Care (StEP-COMPAC). Model performance was compared using the area under the receiver operating characteristic curve (AUROCC).

FINDINGS

In total, we identified 2903 records from our literature search; of which, 2514 (86·6%) unique records were screened, 121 (4·8%) of 2514 full texts were assessed for eligibility, and 29 unique prognostic models were identified. Nine (31·0%) of 29 models had score development reported only, 19 (65·5%) had undergone internal validation, and only four (13·8%) had been externally validated. Data to validate six eligible models were collected in the international external validation cohort study. Data from 11 591 patients were available, with an overall postoperative pulmonary complication rate of 7·8% (n=903). None of the six models showed good discrimination (defined as AUROCC ≥0·70) for identifying postoperative pulmonary complications, with the Assess Respiratory Risk in Surgical Patients in Catalonia score showing the best discrimination (AUROCC 0·700 [95% CI 0·683-0·717]).

INTERPRETATION

In the pre-COVID-19 pandemic data, variability in the risk of pulmonary complications (StEP-COMPAC definition) following major abdominal surgery was poorly described by existing prognostication tools. To improve surgical safety during the COVID-19 pandemic recovery and beyond, novel risk stratification tools are required.

FUNDING

British Journal of Surgery Society.

Effect of smoking on prognosis in patients with non-ischaemic cardiomyopathy

Funding Acknowledgements

Type of funding sources: None.

Background

Cigarette Smoking is a well-known risk factor for increased cardiovascular morbidity and mortality, by causing inflammation, thrombosis, oxidation of low-density lipoprotein cholesterol, and is associated with increased myocardial fibrosis as late gadolinium enhancement on cardiac MRI. Myocardial fibrosis is a powerful factor for predicting arrhythmic deaths and mortality in heart failure patients. Little data is available on effect of smoking on non-ischaemic cardiomyopathy (NICMP). We hypothesize that smoking has an adverse effect on prognosis of patients with NICMP.

Methods

This study included 447 patients with heart failure and reduced left ventricular ejection fraction (LVEF <40%) due to non-ischemic cardiomyopathy, all have coronary angiogram to exclude significant coronary artery disease (>70% stenosis). Mean follow-up duration of 6.34 ± 4.16 years. Composite endpoints include death, ventricular arrhythmia (VA) or hospitalisations for heart failure.

Data were analysed using STATA version 16.0. Cox regression was used to explore the relationships between smoking and composite endpoints. Statistical significance was denoted as p<0.05.

Results

Mean age 63.07 ± 14.19 years, male patients 314 (72%). Mean LVEF 22.89 ± 8.50%. Patients with diabetes mellitus 38%, hypertension 76%, atrial fibrillation 38%, stroke 9%. LDL 2.78 ± 1.04 mmol/l, HbA1c 6.56 ± 1.62%. Patients taking ivabradine 9%, b-blocker 88%, Angiotensin inhibitors/Angiotensin Receptor Blocker 66%, Sacubitrial/ Valsartan 26%, spironolactone 57%, SGLT-2 inhibitor 9%. 40 patients (9%) received device therapy (AICD and Cardiac resynchronization therapy), 19% secondary prevention, 81% for primary prevention.

Smoking (100 cigarette pack year) increased the hazards for composite endpoint by 2.39, [HR (95% CI): 1.074, 5.325; p = 0.033].

Conclusion

Smoking increases the hazards for composite endpoints in patients with NICMP and smoking cessation is recommended.

Bulk Metamaterials Exhibiting Chemically Tunable Hyperbolic Responses

Extraordinary properties of traditional hyperbolic metamaterials, not found in nature, arise from their man-made subwavelength structures causing unique light-matter interactions. However, their preparation requiring nanofabrication processes is highly challenging and merely provides nanoscale two-dimensional structures. Stabilizing their bulk forms via scalable procedures has been a sought-goal for broad applications of this technology. Herein, we report a new strategy of designing and realizing bulk metamaterials with finely tunable hyperbolic responses. We develop a facile two-step process: (1) self-assembly to obtain heterostructured nanohybrids of building blocks and (2) consolidation to convert nanohybrid powders to dense bulk pellets. Our samples have centimeter-scale dimensions typically, readily further scalable. Importantly, the thickness of building blocks and their relative concentration in bulk materials serve as a delicate means of controlling hyperbolic responses. The resulting new bulk heterostructured material system consists of the alternating h-BN and graphite/graphene nanolayers and exhibits significant modulation in both type-I and type-II hyperbolic resonance modes. It is the first example of real bulk hyperbolic metamaterials, consequently displaying the capability of tuning their responses along both in-plane and out-of-plane directions of the materials for the first time. It also distinctly interacts with unpolarized and polarized transverse magnetic and electronic beams to give unique hyperbolic responses. Our achievement can be a new platform to create various bulk metamaterials without complicated nanofabrication techniques. Our facile synthesis method using common laboratory techniques can open doors to broad-range researchers for active interdisciplinary studies for this otherwise hardly accessible technology.

Polycrystalline SnSe with a thermoelectric figure of merit greater than the single crystal

Thermoelectric materials generate electric energy from waste heat, with conversion efficiency governed by the dimensionless figure of merit, ZT. Single-crystal tin selenide (SnSe) was discovered to exhibit a high ZT of roughly 2.2-2.6 at 913 K, but more practical and deployable polycrystal versions of the same compound suffer from much poorer overall ZT, thereby thwarting prospects for cost-effective lead-free thermoelectrics. The poor polycrystal bulk performance is attributed to traces of tin oxides covering the surface of SnSe powders, which increases thermal conductivity, reduces electrical conductivity and thereby reduces ZT. Here, we report that hole-doped SnSe polycrystalline samples with reagents carefully purified and tin oxides removed exhibit an ZT of roughly 3.1 at 783 K. Its lattice thermal conductivity is ultralow at roughly 0.07 W m^-1 K^-1 at 783 K, lower than the single crystals. The path to ultrahigh thermoelectric performance in polycrystalline samples is the proper removal of the deleterious thermally conductive oxides from the surface of SnSe grains. These results could open an era of high-performance practical thermoelectrics from this high-performance material.

A Facile and Effective Ozone Exposure Method for Wettability and Energy-Level Tuning of Hole-Transporting Layers in Lead-Free Tin Perovskite Solar Cells

Lead-free perovskite solar cells (PSCs) have attracted interest among scientists searching for eco-friendly energy harvesting devices. Herein, the effects of ozone exposure on poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) in lead-free tin halide PSCs as a facile and low-cost process for improving device performance are analyzed. Two types of tin-based PSCs and one typical lead-based PSC were fabricated. The ozone exposure on PEDOT:PSS increases the short-circuit current density (J_SC) and the fill factor (FF) of PSCs in all cases with perovskite grain enlargement and hole-mobility enhancement of the devices, respectively. For open-circuit voltage (V_OC), the outcome depends on the band gap and the energy levels of the perovskite films. While ozone exposure treatment is favorable for PEA_0.15FA_0.85SnI₃-based tin PSCs, V_OC decreases with ozone exposure in the case of Ge:EDA_0.01FA_0.98SnI₃-based tin PSCs because of a misalignment of the energy levels. Regardless, the efficiency of PEA_0.15FA_0.85SnI₃-based tin PSCs increases from 8.7 to 10.1% when measured inside a glovebox upon ozone exposure of PEDOT:PSS. The efficiency of Ge:EDA_0.01FA_0.98SnI₃-based tin PSCs increases from 6.8 to 8.1%, and the devices retain an efficiency of 5.0% even after 50 days in air.

Usefulness of Goldberger"s triad to select dilated cardiomyopathy

Funding Acknowledgements

Type of funding sources: None.

Background

Background: In 1982, Goldberger described an electrocardiographic triad (SV1 or SV2 +RV5 or RV6 ≥3.5mV, total QRS amplitude in limb leads ≤0.8mV, and R/S ratio < 1 in lead V4) that was 70% sensitive and >90% specific for detecting severe left ventricular (LV) dysfunction. The pathophysiology of this highly specific ECG triad probably relates to a number of mechanical and vectorial factors associated with congestive heart failure of a variety of etiologies. Left ventricular enlargement causes increased precordial voltage. The horizontal plane vector shifts posteriorly, orthogonal to the frontal plane, causing poor R wave progression and low limb lead voltage. Finally, increased extracellular fluid may preferentially attenuates QRS voltage in the limb leads.

Objective

To test the sensitivity of this triad in patients with non-ischaemic cardiomyopathy and severe left ventricular systolic dysfunction

Methods

Methods: 386 patients mean age 62.45 ± 13.96 years, male 72%, NYHA II-IV, with non-ischaemic cardiomyopathy, 70 had bundle branch block (18%) and mean left ventricular ejection fraction(EF) 22.57 ± 8.62%. 76% hypertension, 39% diabetes mellitus, 32% atrial fibrillation. The electrocardiographic triad was sought in the ECG recorded at time of the echocardiographic study. The mean LV end-diastolic diameter was 5.81 ± 1.53 cm.

Result

Results: 56% patients had SV1 or SV2 +RV5 or RV6 ≥3.5mV, 85% patients had R/S ratio < 1 in lead V4, 19% had total QRS amplitude in limb leads ≤0.8mV. 50% patients had SV1 or SV2 +RV5 or RV6 ≥3.5mV and R/S ratio < 1 in lead V4. Only 6% patients fulfilled the triad.

Conclusions

Conclusion: Goldberger"s triad is an insensitive marker for severe LV dysfunction. Using SV1 or SV2 +RV5 or RV6 ≥3.5mV and R/S ratio < 1 in lead V4 had a sensitivity of 50%. 85% patients had R/S ratio < 1 in lead V4. R/S ratio < 1 in lead V4 is a simple way to select dilated LV.

Prevention of stroke and dementia in elderly patients with atrial fibrillation

Funding Acknowledgements

Type of funding sources: None.

Background

Atrial fibrillation has been shown to associate with greater cognitive decline and increased dementia risk independent of ischaemic stroke. Anti-coagulation was associated with a lower risk of ischemic stroke and positive net clinical benefit in elderly patients.  We hypothesise that elderly patients (>75 years old) with atrial fibrillation on oral anti-coagulants have lower incidence of dementia compared with patients on anti-platelet agents or no anti-thrombotic treatment.

Method

A retrospective study of 747 patients, male 37%, mean age 84.29 ± 5.99 years old with mean follow up of  13.54  ± 3.38  years. 94 % hypertension, 40% diabetes mellitus, 38% ischaemic heart disease, 33% heart failure, 39% previous stroke, mean CHA2DS2-VASc score of 5.23 ± 1.59. 27% patients on oral anti-coagulants, 64% anti-platelet agent and 9% not on any anti-thrombotic medication.

Results

265 patients were diagnosed with dementia, 17 patients were on oral anti-coagulants, 222 patients were on anti-platelet agent. Oral anti-coagulants were associated with lower incidence of dementia compared with anti-platelet agents (p < 0.0001). 26 patients developed dementia were not on any anti-thrombotic agent. 261 patients were readmitted with stroke (2.58%/100 patient year) 182 patients were on anti-platelet agent while 12 were on anti-coagulant (P < 0.0001).

Conclusions

Oral anti-coagulants were associated with lower incidence of dementia and stroke compared with anti-platelet agents in elderly patients with atrial fibrillation.

Exceptionally High Average Power Factor and Thermoelectric Figure of Merit in n-type PbSe by the Dual Incorporation of Cu and Te

Thermoelectric materials with high average power factor and thermoelectric figure of merit (ZT) has been a sought-after goal. Here, we report new n-type thermoelectric system Cu_xPbSe_0.99Te_0.01 (x = 0.0025, 0.004, and 0.005) exhibiting record-high average ZT ∼ 1.3 over 400-773 K ever reported for n-type polycrystalline materials including the state-of-the-art PbTe. We concurrently alloy Te to the PbSe lattice and introduce excess Cu to its interstitial voids. Their resulting strong attraction facilitates charge transfer from Cu atoms to the crystal matrix significantly. It follows the increased carrier concentration without damaging its mobility and the consequently improved electrical conductivity. This interaction also increases effective mass of electron in the conduction band according to DFT calculations, thereby raising the magnitude of Seebeck coefficient without diminishing electrical conductivity. Resultantly, Cu_0.005PbSe_0.99Te_0.01 attains an exceptionally high average power factor of ∼27 μW cm^-1 K^-2 from 400 to 773 K with a maximum of ∼30 μW cm^-1 K^-2 at 300 K, the highest among all n- and p-type PbSe-based materials. Its ∼23 μW cm^-1 K^-2 at 773 K is even higher than ∼21 μW cm^-1 K^-2 of the state-of-the-art n-type PbTe. Interstitial Cu atoms induce the formation of coherent nanostructures. They are highly mobile, displacing Pb atoms from the ideal octahedral center and severely distorting the local microstructure. This significantly depresses lattice thermal conductivity to ∼0.2 Wm^-1 K^-1 at 773 K below the theoretical lower bound. The multiple effects of the dual incorporation of Cu and Te synergistically boosts a ZT of Cu_0.005PbSe_0.99Te_0.01 to ∼1.7 at 773 K.

Towards efficient and stable perovskite solar cells employing non-hygroscopic F4-TCNQ doped TFB as the hole-transporting material

Designing an efficient and stable hole transport layer (HTL) material is one of the essential ways to improve the performance of organic-inorganic perovskite solar cells (PSCs). Herein, for the first time, an efficient model of a hole transport material (HTM) is demonstrated by optimized doping of a conjugated polymer TFB (poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4'-(N-(4-sec-butylphenyl)diphenylamine)]) with a non-hygroscopic p-type dopant F4-TCNQ (2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane) for high-efficiency PSCs. The PSC with the F4-TCNQ doped TFB exhibits the best power conversion efficiency (PCE) of 17.46%, which surpasses that of the reference devices, i.e., 16.64 (LiTFSI + TBP-doped Spiro-OMeTAD as the HTM) and 11.01% (LiTFSI + TBP-doped TFB as the HTM). F4-TCNQ doped TFB was believed to favor efficient charge and energy transfer between the perovskite and the hole transport layer and to reduce charge recombination as evidenced by steady-state photoluminescence (PL) and time-resolved photoluminescence (TRPL) analysis. Moreover, the hydrophobic nature of F4-TCNQ contributed to enhancing the stability of the device under ambient conditions with a RH of 45%. The device reported herein retained ca. 80% of its initial efficiency after 10 days, significantly superior to both LiTFSI + TBP-doped Spiro-OMeTAD (ca. 30%) and LiTFSI + TBP-doped TFB (ca. 10%) based counterparts. This simple yet novel strategy paves the way for demonstrating a promising route for a wide range of highly efficient solar cells and other photovoltaic applications.

Ultrahigh Power Factor and Electron Mobility in n-Type Bi2Te3-x%Cu Stabilized under Excess Te Condition

The thermoelectric (TE) community has mainly focused on improving the figure of merit (ZT) of materials. However, the output power of TE devices directly depends on the power factor (PF) rather than ZT. Effective strategies of enhancing PF have been elusive for Bi₂Te₃-based compounds, which are efficient thermoelectrics operating near ambient temperature. Here, we report ultrahigh carrier mobility of ∼467 cm² V^-1 s^-1 and power factor of ∼45 μW cm^-1 K^-2 in a new n-type Bi₂Te₃ system with nominal composition Cu_xBi₂Te_3.17 (x = 0.02, 0.04, and 0.06). It is obtained by reacting Bi₂Te₃ with surplus Cu and Te and subsequently pressing powder products by spark plasma sintering (SPS). The SPS discharges excess Te but stabilizes the high extent of Cu in the structure, giving unique SPS Cu_xBi₂Te_3.17 samples. The analyzed composition is close to "Cu_xBi₂Te₃". Their charge transport properties are highly unusual. Hall carrier concentration and mobility simultaneously increase with the higher mole fraction of Cu contrary to the typical carrier scattering mechanism. As a consequence, the electrical conductivity is considerably enhanced with Cu incorporation. The Seebeck coefficient is nearly unchanged by the increasing Cu content in contrast to the general understanding of inverse relationship between electrical conductivity and Seebeck coefficient. These effects synergistically lead to a record high power factor among all polycrystalline n-type Bi₂Te₃-based materials.

High Thermoelectric Performance in n-Type Polycrystalline SnSe via Dual Incorporation of Cl and PbSe and Dense Nanostructures

Despite extensive studies on emerging thermoelectric material SnSe, its n-type form is largely underdeveloped mainly due to the difficulty in stabilizing the carrier concentration at the optimal level. Here, we dually introduce Cl and PbSe to induce n-type conduction in intrinsic p-type SnSe. PbSe alloying enhances the power factor and suppresses lattice thermal conductivity at the same time, giving a highest thermoelectric figure of merit ZT of 1.2 at 823 K for n-type polycrystalline SnSe materials. The best composition is Sn_0.90Pb_0.15Se_0.95Cl_0.05. Samples prepared by the solid-state reaction show a high maximum ZT ( ZT_max) ∼1.1 and ∼0.8 parallel and perpendicular to the press direction of spark plasma sintering, respectively. Remarkably, post-ball milling and annealing processes considerably reduce structural anisotropy, thereby leading to a ZT_max ∼1.2 along both the directions. Hence, the direction giving a ZT_max is controllable for this system using the specialized preparation methods for specimens. Spherical aberration-corrected scanning transmission electron microscopic analyses reveal the presence of heavily dense edge dislocations and strain fields, not observed in the p-type counterparts, which contribute to decreasing lattice thermal conductivity. Our theoretical calculations employing a Callaway-Debye model support the experimental results for thermal transport and microscopic structures.

GRUU-Net: Integrated convolutional and gated recurrent neural network for cell segmentation

Cell segmentation in microscopy images is a common and challenging task. In recent years, deep neural networks achieved remarkable improvements in the field of computer vision. The dominant paradigm in segmentation is using convolutional neural networks, less common are recurrent neural networks. In this work, we propose a new deep learning method for cell segmentation, which integrates convolutional neural networks and gated recurrent neural networks over multiple image scales to exploit the strength of both types of networks. To increase the robustness of the training and improve segmentation, we introduce a novel focal loss function. We also present a distributed scheme for optimized training of the integrated neural network. We applied our proposed method to challenging data of glioblastoma cell nuclei and performed a quantitative comparison with state-of-the-art methods. Insights on how our extensions affect training and inference are also provided. Moreover, we benchmarked our method using a wide spectrum of all 22 real microscopy datasets of the Cell Tracking Challenge.

Highly Luminous N3--Substituted Li2MSiO4-δN2/3δ:Eu2+ (M = Ca, Sr, and Ba) for White NUV Light-Emitting Diodes

The N^3--substituted Li₂MSiO₄:Eu²⁺ (M = Ca, Sr, and Ba) phosphors were systematically prepared and analyzed. Secondary-ion mass spectroscopy measurements revealed that the average N^3- contents are 0.003 for Ca, 0.009 for Sr, and 0.032 for Ba. Furthermore, the N^3- incorporation in the host lattices was corroborated by infrared and X-ray photoelectron spectroscopies. From the photoluminescence spectra of Li₂MSiO₄:Eu²⁺ (M = Ca, Sr, and Ba) phosphors before and after N^3- doping, it was verified that the enhanced emission intensity of the phosphors is most likely due to the N^3- doping. In Li₂MSiO₄:Eu²⁺ (M = Ca, Sr, and Ba) phosphors, the maximum wavelengths of the emission band were red-shifted in the order Ca < Ba < Sr, which is not consistent with the trend of crystal field splitting: Ba < Sr < Ca. This discrepancy was clearly explained by electron-electron repulsions among polyhedra, LiO₄-MO _n , SiO₄-MO _n , and MO _n -M'O _n associated with structural difference in the host lattices. Therefore, the energy levels associated with the 4f⁶5d energy levels of Eu²⁺ are definitely established in the following order: Li₂CaSiO₄:Eu²⁺ > Li₂BaSiO₄:Eu²⁺ > Li₂SrSiO₄:Eu²⁺. Furthermore, using the Williamson-Hall (W-H) method, the determined structural strains of Li₂MSiO₄:Eu²⁺ (M = Ca, Sr, and Ba) phosphors revealed that the increased compressive strain after N^3- doping induces the enhanced emission intensity of these phosphors. White light-emitting diodes made by three N^3--doped phosphors and a 365 nm emitting InGaN chip showed the (0.333, 0.373) color coordinate and high color-rendering index (R _a = 83). These phosphor materials may provide a platform for development of new efficient phosphors in solid-state lighting field.

Self-emitting blue and red EuOX (X = F, Cl, Br, I) materials: band structure, charge transfer energy, and emission energy

Self-emitting blue and red EuOX (X = F, Cl, Br, and I) were successfully synthesized and characterized. Far-infrared and Raman measurements revealed that the vibration modes prominently reflected the Eu-O and Eu-X bond characters of these materials. X-ray photoelectron spectroscopy (XPS) of the red-emitting EuOX compounds showed that Eu exclusively existed as Eu3+, while in the blue-emitting EuOX, a mixed Eu3+/Eu2+ state was observed. For the red-emitting EuOX (X = F, Cl, and Br), the maximum wavelengths of the charge-transfer (CT) bands were red-shifted: F → Cl → Br (282, 320, and 330 nm for F, Cl, and Br, respectively). Using one-electron spin-polarized band structure calculations, it was verified that the red-shift of the CT energy from F to Br in EuOX was mainly due to the relative positions of the halogen orbital energies being gradually increased, following the trend in their electronegativity. For the blue-emitting EuOX (X = Cl, Br, and I), the emission band maxima were red-shifted from Cl to I (409, 414, and 432 nm for Cl, Br, and I, respectively), which was quite opposite to the trend predicted based on the spectrochemical series in crystal field theory, which was in good agreement with the previous results of the calculated 5d → 4f transition energies of the Eu2+ activator based on the crystal field theory. Through photoluminescence, UV-visible absorbance, and XPS, it was elucidated that the red emission due to Eu3+ was strongly masked by the intensified blue emission associated with the small amount of Eu2+ in the blue-emitting EuOX (X = Cl, Br, and I). These materials may provide a platform for modeling new phosphors for application in solid-state lighting.

High-Performance Quantum Dot Thin-Film Transistors with Environmentally Benign Surface Functionalization and Robust Defect Passivation

The recent development of high-performance colloidal quantum dot (QD) thin-film transistors (TFTs) has been achieved with removal of surface ligand, defect passivation, and facile electronic doping. Here, we report on high-performance solution-processed CdSe QD-TFTs with an optimized surface functionalization and robust defect passivation via hydrazine-free metal chalcogenide (MCC) ligands. The underlying mechanism of the ligand effects on CdSe QDs has been studied with hydrazine-free ex situ reaction derived MCC ligands, such as Sn₂S₆^4-, Sn₂Se₆^4-, and In₂Se₄^2-, to allow benign solution-process available. Furthermore, the defect passivation and remote n-type doping effects have been investigated by incorporating indium nanoparticles over the QD layer. Strong electronic coupling and solid defect passivation of QDs could be achieved by introducing electronically active MCC capping and thermal diffusion of the indium nanoparticles, respectively. It is also noteworthy that the diffused indium nanoparticles facilitate charge injection not only inter-QDs but also between source/drain electrodes and the QD semiconductors, significantly reducing contact resistance. With benign organic solvents, the Sn₂S₆^4-, Sn₂Se₆^4-, and In₂Se₄^2- ligand based QD-TFTs exhibited field-effect mobilities exceeding 4.8, 12.0, and 44.2 cm²/(V s), respectively. The results reported here imply that the incorporation of MCC ligands and appropriate dopants provide a general route to high-performance, extremely stable solution-processed QD-based electronic devices with marginal toxicity, offering compatibility with standard complementary metal oxide semiconductor processing and large-scale on-chip device applications.

ZnTe Alloying Effect on Enhanced Thermoelectric Properties of p-Type PbTe

We investigate the effect of ZnTe incorporation on PbTe to enhance thermoelectric performance. We report structural, microscopic, and spectroscopic characterizations, ab initio theoretical calculations, and thermoelectric transport properties of Pb_0.985Na_0.015Te-x% ZnTe (x = 0, 1, 2, 4). We find that the solid solubility limit of ZnTe in PbTe is less than 1 mol %. The introduction of 2% ZnTe in p-type Pb_0.985Na_0.015Te reduces the lattice thermal conductivity through the ZnTe precipitates at the microscale. Consequently, a maximum thermoelectric figure of merit (ZT) of 1.73 at 700 K is achieved for the spark plasma-sintered Pb_0.985Na_0.015Te-2% ZnTe, which arises from a decreased lattice thermal conductivity of ∼0.69 W m^-1 K^-1 at ∼700 K in comparison with Pb_0.985Na_0.015Te.

Extraordinary Off-Stoichiometric Bismuth Telluride for Enhanced n-Type Thermoelectric Power Factor

Thermoelectrics directly converts waste heat into electricity and is considered a promising means of sustainable energy generation. While most of the recent advances in the enhancement of the thermoelectric figure of merit (ZT) resulted from a decrease in lattice thermal conductivity by nanostructuring, there have been very few attempts to enhance electrical transport properties, i.e., the power factor. Here we use nanochemistry to stabilize bulk bismuth telluride (Bi₂Te₃) that violates phase equilibrium, namely, phase-pure n-type K_0.06Bi₂Te_3.18. Incorporated potassium and tellurium in Bi₂Te₃ far exceed their solubility limit, inducing simultaneous increase in the electrical conductivity and the Seebeck coefficient along with decrease in the thermal conductivity. Consequently, a high power factor of ∼43 μW cm^-1 K^-2 and a high ZT > 1.1 at 323 K are achieved. Our current synthetic method can be used to produce a new family of materials with novel physical and chemical characteristics for various applications.

K4GeP4Se12: a case for phase-change nonlinear optical chalcogenide

We report on broadband nonlinear optical (NLO) responses from a phase-change chalcogenide compound K(4)GeP(4)Se(12). Its glassy phase exhibits unusual second-harmonic generation (SHG) due to the preservation of local crystallographic order. The SHG efficiency of the glassy form can be boosted by more than 2 orders of magnitude by simple heat treatment. Strong SHG and third-harmonic generation from both glassy and crystalline compounds were characterized over a wide wavelength range of 1.2-4.0 μm. Our results imply that K(4)GeP(4)Se(12) can be utilized for various NLO applications in the mid-infrared spectrum.

Effect of amiloride to retinal toxicity induced by tissue plasminogen activator

Purpose

The effects of amiloride on cellular toxicity caused by tissue plasminogen activator (tPA) in mouse primary retinal cells were investigated.

Methods

Primary retinal cell cultures were maintained using glial conditioned medium. Commercial tPA and L-arginine were added, and the level of cyclic guanosine monophosphate (cyclic-GMP) in the culture supernatant was assessed using an ELISA assay. We measured the cell viability of cultured retinal cells pretreated with three different concentrations of amiloride (1, 10, and 100 µm) in addition to commercial tPA or L-arginine treatment.

Results

After exposing the cultured mouse retinal cells to tPA plus L-arginine or L-arginine alone, cyclic-GMP concentrations were 61.9 ± 5.1 pmole/mL and 63.1 ± 6.1 pmole/mL, respectively. However, the control group had a significantly lower concentration of cyclic-GMP (37.2 ± 3.4 pmole/mL, p < 0.01). The cyclic GMP-dissolved solution did not cause retinal cell death. In the control group and the group treated with 1 µm amiloride and tPA containing L-arginine, the cell viability was 43.7% and 44.5%, respectively. However, cell viability increased to 70.6% with 10 µm amiloride and 78.4% with 100 µm amiloride (p = 0.015).

Conclusions

L-arginine increases intracellular cyclic-GMP and may give rise to retinal cells through this mechanism. In addition, amiloride in concentrations greater than 10 µm protects against L-arginine-induced retinal cell death.

All-solid-state dye-sensitized solar cells with high efficiency

Dye-sensitized solar cells based on titanium dioxide (TiO(2)) are promising low-cost alternatives to conventional solid-state photovoltaic devices based on materials such as Si, CdTe and CuIn(1-x)Ga(x)Se(2) (refs 1, 2). Despite offering relatively high conversion efficiencies for solar energy, typical dye-sensitized solar cells suffer from durability problems that result from their use of organic liquid electrolytes containing the iodide/tri-iodide redox couple, which causes serious problems such as electrode corrosion and electrolyte leakage. Replacements for iodine-based liquid electrolytes have been extensively studied, but the efficiencies of the resulting devices remain low. Here we show that the solution-processable p-type direct bandgap semiconductor CsSnI(3) can be used for hole conduction in lieu of a liquid electrolyte. The resulting solid-state dye-sensitized solar cells consist of CsSnI(2.95)F(0.05) doped with SnF(2), nanoporous TiO(2) and the dye N719, and show conversion efficiencies of up to 10.2 per cent (8.51 per cent with a mask). With a bandgap of 1.3 electronvolts, CsSnI(3) enhances visible light absorption on the red side of the spectrum to outperform the typical dye-sensitized solar cells in this spectral region.

CsSnI3: Semiconductor or metal? High electrical conductivity and strong near-infrared photoluminescence from a single material. High hole mobility and phase-transitions

CsSnI(3) is an unusual perovskite that undergoes complex displacive and reconstructive phase transitions and exhibits near-infrared emission at room temperature. Experimental and theoretical studies of CsSnI(3) have been limited by the lack of detailed crystal structure characterization and chemical instability. Here we describe the synthesis of pure polymorphic crystals, the preparation of large crack-/bubble-free ingots, the refined single-crystal structures, and temperature-dependent charge transport and optical properties of CsSnI(3), coupled with ab initio first-principles density functional theory (DFT) calculations. In situ temperature-dependent single-crystal and synchrotron powder X-ray diffraction studies reveal the origin of polymorphous phase transitions of CsSnI(3). The black orthorhombic form of CsSnI(3) demonstrates one of the largest volumetric thermal expansion coefficients for inorganic solids. Electrical conductivity, Hall effect, and thermopower measurements on it show p-type metallic behavior with low carrier density, despite the optical band gap of 1.3 eV. Hall effect measurements of the black orthorhombic perovskite phase of CsSnI(3) indicate that it is a p-type direct band gap semiconductor with carrier concentration at room temperature of ∼ 10(17) cm(-3) and a hole mobility of ∼585 cm(2) V(-1) s(-1). The hole mobility is one of the highest observed among p-type semiconductors with comparable band gaps. Its powders exhibit a strong room-temperature near-IR emission spectrum at 950 nm. Remarkably, the values of the electrical conductivity and photoluminescence intensity increase with heat treatment. The DFT calculations show that the screened-exchange local density approximation-derived band gap agrees well with the experimentally measured band gap. Calculations of the formation energy of defects strongly suggest that the electrical and light emission properties possibly result from Sn defects in the crystal structure, which arise intrinsically. Thus, although stoichiometric CsSnI(3) is a semiconductor, the material is prone to intrinsic defects associated with Sn vacancies. This creates highly mobile holes which cause the materials to appear metallic.