Highly Efficient Quasi 2D Blue Perovskite Electroluminescence Leveraging a Dual Ligand Composition

Perovskite light-emitting diodes (PeLEDs) are advancing because of their superior external quantum efficiencies (EQEs) and color purity. Still, additional work is needed for blue PeLEDs to achieve the same benchmarks as the other visible colors. This study demonstrates an extremely efficient blue PeLED with a 488 nm peak emission, a maximum luminance of 8600 cd m⁻², and a maximum EQE of 12.2% by incorporating the double-sided ethane-1,2-diammonium bromide (EDBr₂) ligand salt along with the long-chain ligand methylphenylammonium chloride (MeCl). The EDBr₂ successfully improves the interaction between 2D perovskite layers by reducing the weak van der Waals interaction and creating a Dion–Jacobson (DJ) structure. Whereas the pristine sample (without EDBr₂) is inhibited by small stacking number (n) 2D phases with nonradiative recombination regions that diminish the PeLED performance, adding EDBr₂ successfully enables better energy transfer from small n phases to larger n phases. As evidenced by photoluminescence (PL), scanning electron microscopy (SEM), and atomic force microscopy (AFM) characterization, EDBr₂ improves the morphology by reduction of pinholes and passivation of defects, subsequently improving the efficiencies and operational lifetimes of quasi-2D blue PeLEDs.     

Natural Silk Film for Magnesium Protection: Hydrophobic/Hydrophilic Interaction and Self‐Healing Effect

Biodegradable implants are required in order to provide successful treatment of injuries. Temporary magnesium‐based implants with particular properties are needed in cases when it is desirable not only to maintain vital activity, but also to initiate the self‐healing process of damaged bones or tissues as well. Unfortunately, the use of magnesium alloys is limited due to the fast biodegradability of the applied material. The aim of this research is to improve the corrosion resistance of magnesium alloys by sonochemical treatment in silk solution followed by additional layer‐by‐layer deposition of natural silk on the magnesium surface. The sonication process is carried out at a frequency of 20 kHz during 5–10 min, while the duration of the silk layer deposition is 15 min. The corrosion behavior of magnesium substrates modified by natural silk layer‐by‐layer assembly is studied. Magnesium substrates sonochemically treated in silk solution demonstrate three times better corrosion resistance compared to control samples sonochemically treated in water. Additional deposition of a silk layer enhances obtained corrosion resistance by 18 times, resulting in a 54‐fold increase overall.     

Innovations and productivity: the shift during the 2008 crisis

This paper investigates how the recent crisis of 2008 changed relations between innovation and firm performance in Western Europe. We apply a structural framework of CDM modelling, which incorporates different stages of the knowledge creation process and takes into account the complex nature of innovations. The study is based on a balanced panel data of 420 listed manufacturing firms from the U.K., Germany and France. All the information is gathered from common sources, thereby reducing subjectivity, a typical problem in the field. We found, the crisis resulted in appreciable changes in the model. The most important evidence is enhancement of the role of firm resources in the post-recession period. We also reveal larger barriers for innovations, increased uncertainty and lower state dependence in R&D engagement, product creation and economic performance. These results could indicate the ‘cleaning effect’ of the crisis, which has worsened the business environment and enhanced competition.     

Magnesium borohydride as a hydrogen storage material: Properties and dehydrogenation pathway of unsolvated Mg(BH4)2

The decomposition of crystalline magnesium borohydride upon heating was studied using thermal desorption, calorimetry, in situ X-ray diffraction, and solid state NMR. Hydrogen release from Mg(BH₄)₂ occurs in at least four steps via formation of several polyborane intermediate species and includes an exothermic reaction yielding crystalline MgH₂ as an intermediate. The decomposition products may be only partially recharged after the very first step and also via hydrogenation of Mg metal. The intermediate formation of amorphous MgB₁₂H₁₂, was confirmed by ¹¹B NMR. A four-stage pathway for the thermal decomposition of Mg(BH₄)₂ is proposed.     

Changes of Thermodynamic and Structural Properties of Wrinkled Pea Starches (Z‐301 and Paramazent varieties) During Biosynthesis

Starches isolated at different stages of maturation (milky, waxy, complete maturation) of wrinkled peas were investigated by differential scanning calorimetry (DSC) and X‐ray diffraction (XRD). It was shown that the maturation of wrinkled peas is accompanied by changes in the structural and thermodynamic properties of starches. The melting process of milky starches could be approximated by means of a “two‐state” model. The melting process of the waxy and completely maturated starches was described as the melting of a mixture of low and high temperature populations of double‐helical type crystallites, denoted as B‐ and B*‐types, as well as the melting of V_h ‐type crystallites. The relative amounts of the three structures were determined by deconvolution of the calorimetric peaks. The values of the melting cooperative units ( ϑ ) and the thickness of the crystalline lamellae (pitch heights) for starches were determined using mathematical models describing the melting processes. The values of the ϑ for milky, waxy, and completely maturated starches were calculated as 18 and 29 anhydroglucose residues, respectively. The thickness of the crystalline lamellae of B‐type crystals in the milky, waxy, and completely maturated starches were calculated. Structural changes in starch granules during maturation of wrinkled pea are discussed.     

Theoretical Study of the Tautomeric Reactions of Dinitromethane and Its Radical Cation

Reactions of aci-form and diaci-form formation in dinitromethane and its radical cation have been theoretically studied at DFT B3LYP level of theory with 6-31G(d) basis set. The lowest energy structures of the dinitromethane aci-form and diaci-form were optimized. Analogous theoretical study was carried out for dinitromethane radical cation. In connection with observed conformation transitions in aci- and diaci-form, B3LYP level of theory with the 6-31G(d) basis set was used to investigate the relevant parts of dinitromethane and its radical cation ground state potential energy surfaces.     

Computational Study of Main Mechanisms for Gas-Phase Decomposition of 1,1- and 1,2-Dinitroethane

The gas-phase enthalpies of formation of 1,1- and 1,2-dinitroethane and corresponding radical products were calculated using G3B3, CBS-QB3 composite methods and DFT B3LYP level of theory with various basis sets. The enthalpies of the C–N, C–C bonds dissociation and activation enthalpies for HONO elimination were also calculated and compared with available experimental data. It was found that G3B3 calculations do provide a reasonable way to tackle the problem of the decomposition channels of 1,1- and 1,2-dinitroethane. Four main mechanisms for gas-phase decomposition of 1,1- and 1,2-dinitroethane were studied using G3B3 model chemistry. HONO elimination seems to be the most favorable mechanism for the decomposition of 1,2-dinitroethane. However, the difference in energies of the HONO elimination and C–N homolytic bond cleavage in 1,1-dinitroethane does not allow to favor any of these channels, especially at the working temperature. Gauche conformation of 1,2-dinitroethane is calculated to be the lowest-energy minimum.     

Magnesium borohydride as a hydrogen storage material: Synthesis of unsolvated Mg(BH4)2

Different methods for preparation of unsolvated magnesium borohydride, a promising material for hydrogen storage, based on exchange reaction of MgCl₂ with lithium and sodium borohydride in different solvents have been evaluated. A convenient scalable method for synthesis of pure Mg(BH₄)₂ by ball milling a mixture of MgCl₂ and NaBH₄ in diethyl ether has been developed. Crystalline stable low and high temperature phases, as well as a new metastable phase of unsolvated magnesium borohydride have been prepared.     

Pulsed light field of a point source in a scattering medium

Pulsed radiation propagating through a layer of a scattering medium undergoes distortions caused by multiple scattering. The results of numerical calculations of pulse waveforms for media with different scattering phase functions are presented. It is demonstrated that the scattered radiation waveform is not described by diffusion theories even for sufficiently large optical thicknesses (tau approximately 10-20) but is described, as a rule, by a bimodal distribution. Only when the optical thickness significantly increases (tau>100-150), the photon distribution over the free paths acquires the unimodal diffusion form.