Structures of dense glycine and alanine adlayers on chiral Cu(3,1,17) surfaces

Density Functional Theory calculations have been used to predict the structures of dense glycine and alanine adlayers on Cu(3,1,17)(S). Facets of this chiral Cu surface result from adsorbate-induced surface reconstruction when glycine or alanine are adsorbed and annealed on Cu(100). We have calculated the surface energy changes associated with this surface reconstruction. Our results allow the enantiospecificity of this reconstruction following adsorption of enantiopure or racemic alanine on Cu(100) to be discussed. The overall stability of glycine and alanine adlayers on Cu(3,1,17)(S) arises from an interplay between the formation of chemical bonds with the Cu surface, deformations in the adsorbed molecules during adsorption, and intermolecular hydrogen bonds within the adlayer; none of these factors individually dominates.     

Topological characterization of crystallization of gold nanoclusters

In this study we use a new topological structure measure to analyze the local environment of 923 atom gold clusters quenched from the melt, at various quench rates, by molecular dynamics. The crystallization and geometrical rearrangements of the core atoms upon freezing can be clearly observed using our structure measure which is based on planar graphs. Our results support the hypothesis that crystallization is initiated from the surface and proceeds into the cluster core.     

Fractal discrimination of random fractal aggregates and its application in biomarker analysis for blood coagulation

A recent rheological study has established that the fractal dimension, d_f, of an incipient clot, formed at the Gel Point (sol–gel transition) of coagulating blood is a significant new biomarker of haemostasis. In whole healthy blood, incipient clots show a clearly defined value of d_f = 1.7 within a narrow range, which represents a new ‘healthy index’ for normal clotting. The addition of unfractionated heparin significantly prolongs the onset of clot formation with a corresponding reduction of d_f as a function of heparin dose. However, as clots mature they exhibit (i) an expected increase in d_f and (ii) a significant increase to spread of these values, i.e. d_f’s in the range 2.0–2.5, limiting the use of d_f as a discriminant of clot microstructure.The present study, details how and why the spectral dimension, d_s, can be used to accommodate this shortcoming and allow discrimination of mature forms of clot microstructure in indistinguishable in terms of their fractal dimension. To elucidate why d_s permits discrimination a numerical experiment was conducted on computationally generated random fractal aggregates (RFAs) with a priori set value of d_f. Starting from RFAs with a d_f of 1.7, mature RFAs are evolved from these incipient templates by two differing growth processes achieving a final d_f of 2.1. Fractal and statistical analysis of the mature RFAs reveals, for the first time, that their differing internal structure is manifest in the magnitude of d_s. The potential clinical significance of these findings is discussed in terms of the possibility of exploiting the incipient clot’s ability to template the internal arrangement of the mature clot to better predict long term clot susceptibility to lysis.     

The Chemical Vapour Deposition of Tantalum

The effect of the total pressure, feed temperature, deposition temperature, and reaction tube inclination and geometry on the chemical vapour deposition of tantalum from the pentaiodide has been investigated. Transport rates as high as 350 mg hr⁻¹ were achieved in inclined tubes of specific geometry with a feed temperature of 650°C and a deposition temperature of 1200°C. The dependence of the transport rate on the total pressure, and the feed and deposition temperatures has been analysed and suggestions made as to the rate controlling processes.     

Composition,microstructure and mechanical properties of chemically vapour-deposited tantalum

The paper reports the results of a structural investigation of C.V.D. tantalum, which had been deposited on a silica substrate. Deposits at 1000°C were high impurity powders or flakes, at 1100°C (normal deposition temperature) foil-like, these containing much lower silicon contents, being concentrated near the substrate and coming from there by diffusion. The overall silicon content is reported to be due to other kinds of mass transport (i. e. vapour phase transport) and reactions (e.g. Ta with quartz). — Details on the structure and hardness of the Ta layers are given.     

On the Origin of the Non-Arrhenius Na-ion Conductivity in Na3OBr

The sodium-rich antiperovskites (NaRAPs) with composition Na₃OB (B=Br, Cl, I, BH₄, etc.) are a family of materials that has recently attracted great interest for application as solid electrolytes in sodium metal batteries. Non-Arrhenius ionic conductivities have been reported for these materials, the origin of which is poorly understood. In this work, we combined temperature-resolved bulk and local characterisation methods to gain an insight into the origin of this unusual behaviour using Na₃OBr as a model system. We first excluded crystallographic disorder on the anion sites as the cause of the change in activation energy; then identified the presence of a poorly crystalline impurities, not detectable by XRD, and elucidated their effect on ionic conductivity. These findings improve understanding of the processing-structure-properties relationships pertaining to NaRAPs and highlight the need to determine these relationships in other materials systems, which will accelerate the development of high-performance solid electrolytes.