Water structure, dynamics and ion adsorption at the aqueous {010} brushite surface

Understanding the growth processes of calcium phosphate minerals in aqueous environments has implications for both health and geology. Brushite, in particular, is a component of certain kidney stones and is used as a bone implant coating. Understanding the water–brushite interface at the molecular scale will help inform the control of its growth. Liquid-ordering and the rates of water exchange at the brushite–solution interface have been examined through the use of molecular dynamics simulation and the results compared to surface X-ray diffraction data. This comparison highlights discrepancies between the two sets of results, regardless of whether force field or first principles methods are used in the simulations, or the extent of water coverage. In order to probe other possible reasons for this difference, the free energies for the adsorption of several ions on brushite were computed. Given the exothermic nature found in some cases, it is possible that the discrepancy in the surface electron density may be caused by adsorption of excess ions

Solvates, salts, and cocrystals : a proposal for a feasible classification system

The design of pharmaceutical cocrystals has initiated widespread debate on the classification of cocrystals. Current attempts to classify multicomponent crystals suffer from ambiguity, which has led to inconsistent definitions for cocrystals and for multicomponent crystals in general. Inspired by the work of Aitipamula et al. (Cryst. Growth Des. 2012, 12, 2147-2152), we present a feasible classification system for all multicomponent crystals. The present classification enables us to analyze and classify multicomponent crystal structures present in the Cambridge Structural Database (CSD). This reveals that all seven classes proposed are relevant in terms of frequency of occurrence. Lists of CSD refcodes for all classes are provided. We identified over 5000 cocrystals in the CSD, as well as over 12 000 crystals with more than two components. This illustrates that the possibilities for alternative drug formulations can be increased significantly by considering more than two components in drug design

The Effect of Static and Dynamic Stretching on Power Output in Dancers

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Segregation and trapping of erbium during silicon molecular beam epitaxy

3 pages, 4 figures.Erbium surface segregation is observed during growth of Er-doped Si by molecular beam epitaxy on Si(100) at 600 °C. Once a critical Er surface areal density of 2 × 1014 Er/cm2 is reached, enhanced Er trapping is observed, possibly due to the formation of silicide precipitates. Er segregation on Si(100) is fully avoided when growth is performed in an oxygen background pressure of ~ 10 – 10 mbar, due to the formation of Er-O complexes. No Er segregation is observed on Si(111), which is attributed to the formation of epitaxial Er3Si5 precipitates.This work is part of the research program of FOM and was made possible by financial support from NWO, STW, and IOP Electro-Optics. R. Serna acknowledges financial support from CSIC, Spain.Peer reviewe

Proton irradiation induced GaAs solar cell performance degradation simulations using a physics-based model

In this study a recently developed physics-based model to describe the performance degradation of GaAs solar cells upon electron irradiation is applied to analyze the effects of proton irradiation. For this purpose GaAs solar cells with significantly different architectures are subjected to a range of proton irradiation fluences up to 5×1012 H+/cm2. The resulting J−V and EQE characteristics of the cells are measured and compared with the simulations from the model. The model requires individual degradation constants for the SRH lifetimes and the surface recombination velocities as an input. In this study these constants were obtained from the recently determined associated constants for electron irradiation using the particles non-ionizing energy loss (NIEL) values for conversion. The good fit between the simulated and experimentally obtained results demonstrate that this is a valid approach. Moreover, it suggests that the physics based model allows for a good prediction of GaAs cell performance under particle irradiation of any kind independent of the particular cell architecture as long as the layer thicknesses and doping levels are known. In addition the applied proton irradiation levels in this study were not found to induce additional Cu-related degradation in the investigated thin-film cells, indicating that the use of copper foil as a convenient carrier and rear contact does not require reconsideration for thin-film cells intended for space applications

Limiting mechanisms for photon recycling in thin-film GaAs solar cells

Photon recycling mechanisms in single junction thin-film GaAs solar cells are evaluated in this study. Modelling supported by experimentally obtained results is used in order to correlate the reflectance of the cell's rear layers, the photon recycling probability, and the solar cell performance. Solar cells with different top and bottom metallization configurations are produced, and their performance is analyzed from the optical and electrical point of view. It is shown 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, the front grid coverage, usually disregarded in rear mirror focused studies, strongly reduces the photon recycling probability. Furthermore, perimeter and interface recombination hinder the internal radiative efficiency of the solar cells, preventing further increase of the devices' open circuit voltage as a result of improvements of the rear mirror reflectivity. In order to exploit the significant benefit of increased photon recycling probability to the solar cell performance, these limiting mechanisms need to be properly addressed

Crystal structure prediction of organic pigments: quinacridone as an example

The structures of the α, β and γ polymorphs of quinacridone were predicted using Polymorph Predictor software in combination with X-ray powder diffraction patterns of limited quality. The present work demonstrates a method to obtain crystal structures of industrially important pigments when only a low-quality powder pattern is available

Strain Distribution During Growth of Ge/Si(001) and the Effect of Surfactant Layers

Grazing incidence X-ray diffraction has been employed to determine directly the distribution of strain in the plane of the interface during deposition of Ge onto Si(001). The corresponding strain distribution has also been deduced for a relaxed island whose atomic structure has been determined by molecular dynamics. The results illustrate the central role of elastic deformation of islands in the initial stage of strain relief. The results are also compared with those for growth with a Sb surfactant layer which suppresses island formation. An investigation of surfactant-like behaviour is also presented for homoepitaxial growth of Ag on Ag(111), where sub-monolayer coverages of Sb promote a layer-by-layer growth mode over a wide temperature range

Increased Performance of Thin-film GaAs Solar Cells with Improved Rear Interface Reflectivity

The highest efficiencies in single-junction solar cells are obtained with devices based on GaAs. As this material is reaching the limit in material quality, the optimization of the design of the cell becomes more important. In this study we implement a patterning technique to the bottom contact layer of thin-film GaAs solar cells that increases the reflectance of photons to the active layers. Both shallow junction and deep junction devices were evaluated, and for deep junction cells, both the short circuit current and the open circuit voltage increase with the reflectance. The radiative saturation current density also decreases, indicating increased photon recycling. Detailed model simulations are performed to further evaluate the mechanisms leading to the improved performance of the deep junction design. Based on the same model, the possibilities for further improvements utilizing the deep junction are also identified