Comprehensive defect suppression in perovskite nanocrystals for high-efficiency light-emitting diodes

Electroluminescence efficiencies of metal halide perovskite nanocrystals (PNCs) are limited by a lack of material strategies that can both suppress the formation of defects and enhance the charge carrier confinement. Here we report a one-dopant alloying strategy that generates smaller, monodisperse colloidal particles (confining electrons and holes, and boosting radiative recombination) with fewer surface defects (reducing non-radiative recombination). Doping of guanidinium into formamidinium lead bromide PNCs yields limited bulk solubility while creating an entropy-stabilized phase in the PNCs and leading to smaller PNCs with more carrier confinement. The extra guanidinium segregates to the surface and stabilizes the undercoordinated sites. Furthermore, a surface-stabilizing 1,3,5-tris(bromomethyl)-2,4,6-triethylbenzene was applied as a bromide vacancy healing agent. The result is highly efficient PNC-based light-emitting diodes that have current efficiency of 108 cd A−1 (external quantum efficiency of 23.4%), which rises to 205 cd A−1 (external quantum efficiency of 45.5%) with a hemispherical len

Ferroelectric-Based Catalysis: Switchable Surface Chemistry

The maximum efficiency of a fixed catalytic surface occurs when the adsorbate–surface interaction strength is optimal as per the Sabatier principle: strong enough to drive the reactions forward but weak enough to permit the products’ desorption. Such a compromise can fundamentally limit catalytic activity. One solution is to create a surface with switchable activity between strong binding (rapid dissociation) and weak binding (easy desorption). On the basis of first-principles theory, we describe a class of catalysts comprising an epitaxial monolayer of a transition metal oxide on an oxide ferroelectric substrate in which reversing the ferroelectric polarization state switches the surface activity between these two limits. As an example, a CrO₂ monolayer on ferroelectric PbTiO₃ permits direct NO_<i>x</i> decomposition and CO oxidation while circumventing oxygen and sulfur poisoning. Our computed binding energy trends are explained by a generalization of the canonical d-band model for transition metals to metal oxide surfaces combined with charge transfer effects

Water in hybrid perovskites: Bulk MAPbI3 degradation via super-hydrous state

Here, first-principles density functional theory calculations are presented which reveal how water incorporation in hybrid halide perovskite [CH3NH3]PbI3 (MAPbI3) catalyzes the phase transition to the ([CH3NH3]PbI3.H2O edge-sharing) monohydrate (colorless) phase, eliminating its favorable photovoltaic properties. First, fundamental chemical and electrostatic interactions between water and each component of MAPbI3 are analyzed, demonstrating their dependence on water concentration. Second, the energetics of incorporated water is explored, leading to the discovery of spontaneous phase segregation into dry regions and regions with more than one water per formula unit—termed the “super-hydrous state.” Third, the properties of the super-hydrous state are analyzed, including the acceleration of octahedron breaking and rearrangement by the high water density. This reveals the phase transformation to be a bulk process, initiated at the super-hydrous regions. This paper concludes with a discussion of how this super-hydrous model explains disparate recent experimental observations concerning the water-induced transition from (black) perovskite to edge-sharing PbI2 (yellow) phase

A study on protozoan infections (Giardia, Entamoeba, Isoapora and Cryptosporidium) in stray dogs in Ilam province

Giardia, Entamoeba, Isospora and Cryptosporidium are important protozoan parastites that caused diarrhea in human and animals. In the present study, fecal samples were collected fresh, directly from the rectum of 112 stray dogs in Ilam province. Giardia and Entamoeba were concentrated by using the formalin ether sedimentation method followed by the trichrome and iodine staining technique andCryptosporidium  oocysts  were  concentrated  by  using  the  formalin  ether  sedimentation  method  followed by the modified Ziehl-Neelsen staining technique. Of 112 stray dogs, protozoan infections were detected from feces of 46 dogs (41.07%) that Giardia infection was detected from feces of 21 dogs (18.75%), Isospora 17 (15.17%), Cryptosporidium 8 (7.14%) and synchronization infection to 2 protozoan in 9 dogs (8.03%) and to 3 protozoan in 3 (2.67%). In the present study not observed to Entamoeba. No statistically significant differences in prevalence of protozoan parasites occurred between female (34.21 %) and male (55.5 %) stray dogs (p>0/05). But statistically significant differences in prevalence occurred between 1≥0 and 0 ≥1 stray dogs (p>0/05). So that stray dogs of Ilam province can cause infection of human water and food sources

Survey of Experimental Contamination to Ichthyophthirius Multifiliis in Cultural Rainbow Trout Consequently Vaccination with Aquavac Garvetil

Branch. 4 Under graduated students of veterinary medicine and members of young researcher club of Tabriz, Islamic Azad University, Tabriz branch, Tabriz, Iran Garedaghi Y., Khayat Nouri M.H., Kakekhani S., Nazeri M.; Survey of experimental contamination to ichthyophthirius multifiliis in cultural rainbow trout consequently vaccination with aquavac garvetil ABSTRACT The rainbow trout is the only cold water fish in Iran which has specific economic importance. One of the major bacterial diseases among the rainbow trout is streptococcosis which can be controlled through aquavac garvetil vaccine. It has been shown that this vaccine has stimulation effects on specific and non-specific immune system in the fish. So the aim of this study was determination of Ichthyophthirius experimental infectious in rainbow trout after aquavac garvetil vaccination. In this study, 2000 fish (1g) randomly selected and ten infected fish by Ichthyophthirius added to pool after 15 days. After 60 days, fishes randomly divided in control and treatment groups. In treatment group, vaccination was done in two stages. First stage in day 67 which fish were sunk in aquavac garvetil vaccine and in second stage vaccine were administrated orally in day 127. In control group, vaccine were not used. After one month, in both groups, 500 fish randomly were selected and anesthetized, after wet mount preparation the numbers of parasites were counted. Mean of number of parasites compared in control and treatment groups. Results showed that in treatment group after vaccination the number of parasites significantly decreased (p&lt;0.05) compared with control group. This effect of aquavac garvetil vaccine is probably via stimulating effect of this agent on nonspecific immune system in fishes. However study of the mechanism of this vaccine in decreasing of Ichthyophthirius infections needs to more investigation

Study of sleep habits and their effective factors in children admitted to Amirkabir Hospital, Arak

Introduction: Sleep disorders are the most common behavioral complaints in children. Therefore, this study was conducted to determine the sleep habits of children admitted to Amirkabir Hospital, Arak, Iran. Material & Methods: In this descriptive cross-sectional study, children aged 4 to 12 years admitted to Amirkabir Hospital clinic in 2021 were randomly studied. Data obtained from the Children's Sleep Habits Questionnaire were analyzed using SPSS24.0 software. Findings: A total of 295 children with a mean age of 7.26±2.27 years were studied. The prevalence of the disorder in sleep habits was 67.4%. Among the children with disturbed sleep habits, 193 (96.9%) had poor sleep habits and 6 (3.1%) had average sleep habits. The total sleep habits score was significantly higher in girls, unwanted children, and children with divorced parents, low parental education level, and incompatible parents (P0.05). Discussion & Conclusion: In this study, most children showed disturbed sleep habits. Considering that children's poor sleep habits may be a contributing factor for stress, pressure, and tension in the family, mass education and psychiatric intervention are needed in this regard

Ferroelectric surface chemistry: First-principles study of the PbTiO[subscript 3] surface

Ferroelectric surfaces provide a promising method for modifying surface reactions via an external electric field, which can potentially provide an avenue for tunable molecular binding and surface catalysis. Using first-principles density functional theory, we investigate how the properties of the PbTiO[subscript 3] surface vary with polarization and how these changes affect CO[subscript 2] and H[subscript 2]O adsorption. We find that the polarized stoichiometric surfaces cancel the depolarizing field with an electronic reconstruction, which has a large effect on molecular binding energies. However, thermodynamically, the system will instead cancel the depolarizing field by adjusting the surface stoichiometry. Variation of the polarization and the environmental conditions can thus be used to systematically tune the surface chemistry over a wide range. In addition, we consider the addition of several different catalytic monolayers to the PbTiO[subscript 3] surface, and we find that additional surface layers can be used to modify the binding of molecules to the surface while still responding to the polarization of the substrate.National Science Foundation (U.S.). Materials Research Science and Engineering Centers (Program) (DMR 0520495)National Science Foundation (U.S.). Materials Research Science and Engineering Centers (Program) (DMR 1119826)National Science Foundation (U.S.) (Grant CNS 0821132)National Science Foundation (U.S.) (Teragrid Project Grant TG-MCA08X007

Relationship between the Surface Reconstruction of Nickel Phosphides and Their Activity toward the Hydrogen Evolution Reaction

Nickel phosphides (NixPy) are a class of materials that are made out of earth abundant elements and have shown relatively high hydrogen evolution reaction (HER) activity. Here, we perform first-principles density functional theory (DFT) calculations to systematically investigate the stoichiometric and nonstoichiometric surface reconstructions of six different NixPy, i.e., Ni3P, Ni12P5, Ni2P, Ni5P4, NiP2, and NiP3, under electrochemical conditions and to illustrate the implications of such reconstructions for the catalytic activity toward HER. Our results can explain a broad range of experimental observations on the HER activity of NixPy in a unified framework. For the majority of cases, our protocol can closely reproduce the experimentally measured overpotential trends in the literature, which validates its usefulness in generating physical insight into the surface phenomena responsible for HER activity. We find that, among the NixPy studied here, Ni3P and Ni5P4 are the most active catalysts toward HER in acid, whereas Ni5P4 performs the best compared to other NixPy in base, in agreement with previous experimental reports. We show that P-vacancy formation in base renders the Ni-rich NixPy (Ni3P, Ni12P5, Ni2P, and Ni5P4) worse performers in base when compared to their activity in acid and hence propose that introducing nonmetals, which are less prone to dissolution, can improve their catalytic performance. In terms of active site design, we find Ni3 hollow sites bind H too strongly and surface P sites with P–Ni bonds bind H too weakly. On the other hand, we identify that surface P sites with P–P bonds offer the best catalytic performances, and therefore, we predict that active site engineering to maximize the abundance of such surface motifs can further improve the HER activity. Moreover, we unravel the nature of H binding across the material class for different binding motifs via electronic structure theory analysis. The chemical insight we provide in this work can help rationalize the search for materials composed of inexpensive earth abundant elements that provide improved HER catalytic activity