One-pot synthesis, crystallization and deracemization of isoindolinones from achiral reactants

The synthesis, crystallization, and complete solid-state deracemization of isoindolinones was realized in one pot simply by grinding achiral reaction components in a suitable solvent with an achiral catalyst. Previously, this concept was applied to a reversible reaction, but herein we showed that it could also be used in combination with reactions in which product formation is irreversible. A controlled final configuration of the product was obtained by using small amounts of chiral additives or seed crystals of the product

Twinning superlattices in indium phosphide nanowires

Here, we show that we control the crystal structure of indium phosphide (InP) nanowires by impurity dopants. We have found that zinc decreases the activation barrier for 2D nucleation growth of zinc-blende InP and therefore promotes the InP nanowires to crystallise in the zinc blende, instead of the commonly found wurtzite crystal structure. More importantly, we demonstrate that we can, by controlling the crystal structure, induce twinning superlattices with long-range order in InP nanowires. We can tune the spacing of the superlattices by the wire diameter and the zinc concentration and present a model based on the cross-sectional shape of the zinc-blende InP nanowires to quantitatively explain the formation of the periodic twinning.Comment: 18 pages, 4 figure

Dark curve analysis of thin-film GaAs solar cells, with a focus on photon recycling approaches

Multiple studies have been recently conducted towards increasing photon recycling in thin-film GaAs solar cells. It has been established that the photon recycling probability increases with the rear mirror reflectance and solar cell thickness, which results in the increase of the devices open circuit voltage. However, perimeter and interface recombination have been shown to hinder the internal radiative efficiency of the solar cells, preventing further increase of the devices' performance as a result of improvements to the rear mirror reflectivity. In this study, we present an in-depth analysis of the effects that interface recombination has on the device performance, focused on the solar cells dark characteristics. In order to fully exploit the significant benefit of an increased photon recycling probability to the solar cell performance, these limiting mechanisms need to be properly addressed

Critical vacancy density for melting in two-dimensions:The case of high density Bi on Cu(111)

The two-dimensional melting/solidification transition of the high density [2012] phase of Bi on Cu(111) has been studied by means of low energy electron microscopy (LEEM). This well defined phase has an ideal concentration of one Bi atom per two Cu surface atoms (θ Bi = 0.500). The Bi density is determined accurately in situ and the highest melting temperature of 538 K occurs at exactly θ Bi = 0.500. A significantly reduced melting temperature is observed for lower Bi densities (θ Bi 0.500. At |Δ θ Bi| = 0.015 the melting temperature is reduced by about 20 K. This lowering of the melting temperature is attributed to a critical vacancy density at melting and we propose that this quantity triggers the 2D solid-liquid phase transition. For this particular system, the critical vacancy fraction for melting amounts to 5%-6%. Above θ Bi = 0.500 and near melting a homogeneous, unilaterally compressed phase, '[2012]' is observed, with a density that increases continuously with coverage. It is commensurate along and incommensurate along The ability to distinguish between Bi accommodated within the '[2012]' phase and Bi residing on top as a lattice gas by applying LEEM is of crucial importance for the analysis

Electron radiation–induced degradation of GaAs solar cells with different architectures

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NaI as suitable alkali halide hydrate for domestic thermochemical heat storage

The limits and potentials of alkali (Li - Cs) halides (F - I) as salt hydrate-based thermochemical heat storage materials are studied. Most alkali halides are found unsuitable, and only the hydrates of sodium iodide (NaI) and sodium bromide (NaBr) were investigated experimentally. We confirmed that both have high energy densities of 1.5 GJ/m3 and 1.6 GJ/m3 respectively, based on the crystal structures of the dihydrate phases. NaI demonstrated full cyclic stability at water vapor pressures of 12 and 14.5 mbar, but NaBr did not show rehydration at these conditions. Therefore, NaBr was deemed unsuitable for domestic applications. For the NaI – H2O system, we have measured the p,T equilibrium line between the hydration states and constructed p,T and T,x – phase diagrams. This showed that the hydration temperature is 42 °C for 12 mbar water vapor pressure which is enough for domestic space heating. Additionally, the phase diagrams revealed an incongruent melting point where the NaI·2H2O is in equilibrium with the anhydrate and a saturated aqueous NaI solution. This melting can overlap with dehydration and thereby hinders the cyclability, since in the melting process part of the salt is dissolved which blocks the pores formed during dehydration. Therefore, the performance of NaI can be improved by ensuring dehydration is completed below the incongruent melting point of 68 °C. We also found that pre-cycling can prevent deliquescence which is expected to occur at 25 °C and 12 mbar. Overall, NaI could be a candidate for low temperature heat storage.</p

Epitaxy of Anthraquinone on (100) NaCl: A Quantitative Approach

A growth cell suitable for microscopic in situ observation of well-controlled crystal growth from the vapor phase is used to study the heteroepitaxial growth of anthraquinone crystals on a (100) NaCl substrate. In this, the morphology, orientation, nucleation, and growth rate of the crystals is studied as a function of driving force, Δμ/kT. At the lowest Δμ/kT, the crystals are block-shaped and show no preferential orientation with respect to the substrate. Increasing the driving force leads to the growth of oriented block- and needle-shaped crystals, which nucleate from macrosteps on the substrate. At the highest Δμ/kT, crystals nucleate on the flat surface areas or at monatomic steps on the substrate, resulting in a dramatic increase in epitaxial needle density. Growth rate measurements show an exponential behavior as a function of Δμ/kT. In all cases, the supply of growth units proceeds via surface diffusion over the NaCl substrate surface toward the anthraquinone crystals. At the lowest Δμ/kT, growth is partly limited by integration of the growth units at the crystal surfaces. At intermediate driving force, kinetic roughening sets in, leading to rounded needle tips. At the highest supersaturation, growth is completely governed by the supply of growth units via surface diffusion, leading to tip splitting as a consequence of morphological instability

Towards continuous deracemization via racemic crystal transformation monitored by in-situ Raman spectroscopy

In this work, we demonstrate a semi-batch solid-state deracemization process for N-(2- chlorobenzylidene)-phenylglycine amide (NCPA), a complex chiral polymorphic system that involves three types of crystalline racemates (racemic compound and conglomerate forms I and II). In this process, gradually fed metastable racemic compound crystals are converted in situ to crystals of the preferred (seeded) enantiomer under grinding conditions through a series of solvent- mediated transformations in a racemizing solution. The phase diagram for this system shows that while conglomerate form II is stable at the conditions examined (acetonitrile at 21°C), form I crystals of a single enantiomer (used as seeds) are unstable at (nearly) racemic compositions and convert to the racemic compound upon addition of the racemization catalyst. Thus, care needs to be exercised in order to fully convert form I to form II before addition of the racemization catalyst in order to prevent the undesired crystallization of the racemic compound. This can be achieved by adding a small amount of water, which is found to enhance the nucleation and growth kinetics of the most stable conglomerate form II, eventually leading to complete deracemization. Importantly, we show that this special deracemization process can be easily monitored online by Raman spectroscopy, which gives access to the evolution of the solid phase composition. For the studied system, this information can in turn be used to directly estimate the solid-phase enantiomeric excess online throughout the process, as long as conglomerate crystals of the counter enantiomer do not form

Genetically predicted cortisol levels and risk of venous thromboembolism

Introduction - In observational studies, venous thromboembolism (VTE) has been associated with Cushing’s syndrome and with persistent mental stress, two conditions associated with higher cortisol levels. However, it remains unknown whether high cortisol levels within the usual range are causally associated with VTE risk. We aimed to assess the association between plasma cortisol levels and VTE risk using Mendelian randomization. Methods - Three genetic variants in the SERPINA1/SERPINA6 locus (rs12589136, rs11621961 and rs2749527) were used to proxy plasma cortisol. The associations of the cortisol-associated genetic variants with VTE were acquired from the INVENT (28 907 cases and 157 243 non-cases) and FinnGen (6913 cases and 169 986 non-cases) consortia. Corresponding data for VTE subtypes were available from the FinnGen consortium and UK Biobank. Two-sample Mendelian randomization analyses (inverse-variance weighted method) were performed. Results - Genetic predisposition to higher plasma cortisol levels was associated with a reduced risk of VTE (odds ratio [OR] per one standard deviation increment 0.73, 95% confidence interval [CI] 0.62–0.87, p Conclusions - This study provides evidence that genetically predicted plasma cortisol levels in the high end of the normal range are associated with a decreased risk of VTE and that this association may be mediated by blood pressure. This study has implications for the planning of observational studies of cortisol and VTE, suggesting that blood pressure traits should be measured and accounted for