Decrease In Bond Energy Research Articles

Fabrication of red-emitting perovskite LEDs by stabilizing their octahedral structure.

Light-emitting diodes (LEDs) based on metal halide perovskites (PeLEDs) with high colour quality and facile solution processing are promising candidates for full-colour and high-definition displays1-4. Despite the great success achieved in green PeLEDs with lead bromide perovskites5, it is still challenging to realize pure-red (620-650 nm) LEDs using iodine-based counterparts, as they are constrained by the low intrinsic bandgap6. Here we report efficient and colour-stable PeLEDs across the entire pure-red region, with a peak external quantum efficiency reaching 28.7% at 638 nm, enabled by incorporating a double-end anchored ligand molecule into pure-iodine perovskites. We demonstrate that a key function of the organic intercalating cation is to stabilize the lead iodine octahedron through coordination with exposed lead ions and enhanced hydrogen bonding with iodine. The molecule synergistically facilitates spectral modulation, promotes charge transfer between perovskite quantum wells and reduces iodine migration under electrical bias. We realize continuously tunable emission wavelengths for iodine-based perovskite films with suppressed energy loss due to the decrease in bond energy of lead iodine in ionic perovskites as the bandgap increases. Importantly, the resultant devices show outstanding spectral stability and a half-lifetime of more than 7,600 min at an initial luminance of 100 cd m-2.

Investigation of structural, electronic and optical properties of potassium and lithium based ternary Selenoindate: Using first principles approach

Here we reported the first principle-based calculations for the structural and optoelectronic properties of AInSe2 (A ​= ​K and Li) chalcopyrite type single crystals with-in the framework of density functional theory (DFT). The calculated structural parameters using the local density approximation (LDA) and general gradient approximation (GGA) are in a best agreement with existing experimentals and others theoretical results. The band structures and density of states of these materials are investigated and discussed in detail. Our calculations reveal a direct band-gap semiconductor type nature for both materials. The calculated band gaps follow that Eg (LiInSe2) ​> ​Eg (KInSe2) showing a good agreement for a decrease in bond energy for the corresponding In-s and Se-p anti-bonding orbital states. Furthermore, the frequency dependent linear optical properties, such as the complex dielectric functions, energy loss function, absorption coefficient, reflectivity, refractive index, the extinction coefficient and the real part of optical conductivity are also computed and discussed in detail. Our calculated optical results were found to be in a good agreement with the results from the literature There exists a significant variation in optical characteristics of both these materials. Our predicted calculated results would guide to understand the experimental and theoretical work on the basic material properties of these materials including crystal structures, optoelectronic properties, as well as their device applications.

Hexaphenylethanes with an Ultralong C–C Bond: Expandability of the C–C Bond in Highly Strained Tetraarylpyracenes

Abstract Over the past few decades, many studies have been conducted on ultralong C–C bonds (bond length greater than 1.7 Å). This highlight review discusses the molecular design of ultralong C–C bonds and their bonding properties, especially their “expandability.” In particular, the ultralong C–C bonds in tetraarylpyracene derivatives can change in length by adopting a slightly different conformation in the crystalline state. This expandability of ultralong C–C bonds could be due to the smaller decrease in bond energy at a longer interatomic distance (>1.7 Å). This interesting property can be applied to stimulus-responsive materials, as illustrated in the thermochromism of a bis(methylacridan)-substituted pyracene crystal, since the thermally induced change in bond-length modifies the HOMO–LUMO gap.

Study on Preparation of Mullite Powder Using Fly Ash by Mechanochemical Method

This paper studies the structural changes of the mixture of fly ash and A12O3 grinded by planetary ball mill . By investigating the structure of the ground product by SEM, XRD and FT-IR, the mechanism of mullite formation is discussed. The crystal structure of the mixture was destroyed by the grinding of planetary ball mill, and with the grinding time increases, the specific surface area of the mixture increases as well. And this leads to the decrease of bond energy, the increase of the internal energy and the decrease of the activation energy. After this process,uniform mixture and direct formation of signal phase mullite can be obtained from the mixture grinded for 30 hours and calcined at 1150°C for 2 hours and the temperature for mixture ungrinded needs to reach 1450°C.

In Silico Study of Human Gap Junction Beta-2 Protein by Homology Modeling

Abstract Asp66his, Asp54Lys, and Asp50Asn are mutations in connexin 26 that are observed in the clinic and give rise to autosomal dominant syndromes. They are the result of point mutations in the human gap junction β-2 gene. In order to investigate the structural mechanism of Bart-Pumphrey Syndrome, Keratitis-Ichthyosis-Deafness Syndrome, and Vohwinkel Syndrome, homology model-ing was carried out. Asp66 has direct contact with Asn62 by two hydrogen bonds in the wild-type protein, and in Asp66His, the biggest change observed is a tre-mendous energy increase caused by hydrogen bond breakage to Asn62. Shifts in the side chain and new hy-drogen bond formation are observed for Lys54 com-pared to the wild-type protein (Asn54) and result in clos-er contact to Val84. Asp50Asn causes a significant de-crease in bond energy, and residual charge reversal re-pels the ion and metabolites and, hence, inhibits their transportation. Such perturbations are likely to be a fac-tor contributing to abnormal functioning of ion channels, resulting cell death and disease.Keywords: Bart-Pumphrey syndrome, connexin 26, gap junction, β-2 protein, hearing impairment, Keratitis-Ich-thyosis-Deafness syndrome, knuckle pads, leukonychia, vohwinkel syndrome

Low-temperature solid-phase-crystallization in Si 1− xGe x/SiO 2

Solid-phase crystallization (SPC) properties of Si 1− x Ge x ( x=0–0.3) layers on SiO 2 have been investigated by using ellipsometric spectroscopy. Crystallinity of the Si 1− x Ge x layers is significantly affected by both annealing-time and Ge-concentration x. The crystallinity abruptly increases at the end of the incubation time and gradually saturated during the crystallization time. As x increases, we have found that the nucleation is significantly enhanced and the estimated incubation time of x=0.3 is about 1/100 of that of pure Si ( x=0). The crystallization time defined as the time to complete SPC after nucleation also significantly decreases with increasing x. Such changes of the crystallinity in the Ge-doped Si 1− x Ge x layers perhaps originates from the difference between bond energies of SiSi, SiGe, and GeGe. The decrease of bond energy activates both nucleation and crystal-growth process in Si 1− x Ge x layers.