Pnictogens Allotropy and Phase Transformation during van der Waals Growth

Pnictogens have multiple allotropic forms resulting from their ns2 np3 valence electronic configuration, making them the only elemental materials to crystallize in layered van der Waals (vdW) and quasi-vdW structures throughout the group. Light group VA elements are found in the layered orthorhombic A17 phase such as black phosphorus, and can transition to the layered rhombohedral A7 phase at high pressure. On the other hand, bulk heavier elements are only stable in the A7 phase. Herein, we demonstrate that these two phases not only co-exist during the vdW growth of antimony on weakly interacting surfaces, but also undertake a spontaneous transformation from the A17 phase to the thermodynamically stable A7 phase. This metastability of the A17 phase is revealed by real-time studies unraveling its thickness-driven transition to the A7 phase and the concomitant evolution of its electronic properties. At a critical thickness of ~4 nm, A17 antimony undergoes a diffusionless shuffle transition from AB to AA stacked alpha-antimonene followed by a gradual relaxation to the A7 bulk-like phase. Furthermore, the electronic structure of this intermediate phase is found to be determined by surface self-passivation and the associated competition between A7- and A17-like bonding in the bulk. These results highlight the critical role of the atomic structure and interfacial interactions in shaping the stability and electronic characteristics of vdW layered materials, thus enabling a new degree of freedom to engineer their properties using scalable processes

May Measurement Month 2018: a pragmatic global screening campaign to raise awareness of blood pressure by the International Society of Hypertension

Aims Raised blood pressure (BP) is the biggest contributor to mortality and disease burden worldwide and fewer than half of those with hypertension are aware of it. May Measurement Month (MMM) is a global campaign set up in 2017, to raise awareness of high BP and as a pragmatic solution to a lack of formal screening worldwide. The 2018 campaign was expanded, aiming to include more participants and countries. Methods and results Eighty-nine countries participated in MMM 2018. Volunteers (≥18 years) were recruited through opportunistic sampling at a variety of screening sites. Each participant had three BP measurements and completed a questionnaire on demographic, lifestyle, and environmental factors. Hypertension was defined as a systolic BP ≥140 mmHg or diastolic BP ≥90 mmHg, or taking antihypertensive medication. In total, 74.9% of screenees provided three BP readings. Multiple imputation using chained equations was used to impute missing readings. 1 504 963 individuals (mean age 45.3 years; 52.4% female) were screened. After multiple imputation, 502 079 (33.4%) individuals had hypertension, of whom 59.5% were aware of their diagnosis and 55.3% were taking antihypertensive medication. Of those on medication, 60.0% were controlled and of all hypertensives, 33.2% were controlled. We detected 224 285 individuals with untreated hypertension and 111 214 individuals with inadequately treated (systolic BP ≥ 140 mmHg or diastolic BP ≥ 90 mmHg) hypertension. Conclusion May Measurement Month expanded significantly compared with 2017, including more participants in more countries. The campaign identified over 335 000 adults with untreated or inadequately treated hypertension. In the absence of systematic screening programmes, MMM was effective at raising awareness at least among these individuals at risk

Global urban environmental change drives adaptation in white clover

Urbanization transforms environments in ways that alter biological evolution. We examined whether urban environmental change drives parallel evolution by sampling 110,019 white clover plants from 6169 populations in 160 cities globally. Plants were assayed for a Mendelian antiherbivore defense that also affects tolerance to abiotic stressors. Urban-rural gradients were associated with the evolution of clines in defense in 47% of cities throughout the world. Variation in the strength of clines was explained by environmental changes in drought stress and vegetation cover that varied among cities. Sequencing 2074 genomes from 26 cities revealed that the evolution of urban-rural clines was best explained by adaptive evolution, but the degree of parallel adaptation varied among cities. Our results demonstrate that urbanization leads to adaptation at a global scale

Towards atomic resolution in sodium titanate nanotubes using near-edge X-ray-absorption fine-structure spectromicroscopy combined with multichannel multiple-scattering calculations

International audienceRecent advances in near-edge X-ray-absorption fine-structure spectroscopy coupled with transmission X-ray microscopy (NEXAFS-TXM) allow large-area mapping investigations of individual nano-objects with spectral resolution up to E/Delta E = 104 and spatial resolution approaching 10 nm. While the state-of-the-art spatial resolution of X-ray microscopy is limited by nanostructuring process constrains of the objective zone plate, we show here that it is possible to overcome this through close coupling with high-level theoretical modelling. Taking the example of isolated bundles of hydrothermally prepared sodium titanate nanotubes ((Na,H)TiNTs) we are able to unravel the complex nanoscale structure from the NEXAFS-TXM data using multichannel multiple-scattering calculations, to the extent of being able to associate specific spectral features in the O K-edge and Ti L-edge with oxygen atoms in distinct sites within the lattice. These can even be distinguished from the contribution of different hydroxyl groups to the electronic structure of the (Na,H)TiNTs

Vibrational spectroscopy in the electron microscope

Vibrational spectroscopies using infrared radiation In the past two decades, the performance of electron microscopes has been greatly improved by the introduction of multipole-based aberration correction technology Because of recent progress, we are now able to answer the question in the positive. The progress has taken place on three principal fronts: (1) the energy resolution of EELS carried out in the electron microscope has been improved to around 10 meV; (2) the EELS-STEM instrument has been optimized so that the electron probe incident on the sample contains a current sufficient to perform EELS experiments even when the energy width of the probe is ,10 meV and its size ,1 nm; and (3) the tail of the intense zero loss peak (ZLP) in the EELS spectrum has been reduced so that it does not obscure the vibrational features of interest. The innovations responsible for the progress are (1) a monochromator of a new design 17 , which is able to reach an energy resolution comparable to the highest resolution attained previously The observation of vibrational peaks due to hydrogen in TiH 2 and in the epoxy resin is especially interesting. In TiH 2 , hydrogen is mobile and bound only weakly, which results in the relatively low (for hydrogen) vibrational energy of 147 meV. In epoxy resin, hydrogen is mostly bound to carbon, and 360 meV (2,900 cm 21 ) is a typical C-H stretch vibrational energy 1-3 . Up to now, hydrogen has been essentially invisible in electron microscopes, its presence typically inferred from the modified electron distribution due to the electron it contributes to the sample's electron density distribution. Its unambiguous detection by vibrational spectroscopy promises to provide a general technique for hydrogen Macmillan Publishers Limited. All rights reserved ©2014 detection in the many hydrogen-containing materials studied by electron microscopy. Another attractive prospect involves analysing the types of covalent hydrogen bonding present in microscopic amounts of matter, with H-C, H-N, H-O and other types of hydrogen bonds giving distinct vibrational frequencies 1-3 . The width of the vibrational peaks shown in The vibrational signal was obtained by subtracting the background under the peak at 138 meV in all the spectra, which were similar to the spectrum shown in Aloof beams losing energy to delocalized electronic excitations (such as surface plasmons) have been studied extensively in low-loss EELS The spatial resolution obtainable with the aloof signal is comparable to that of tip-enhanced optical spectroscopy 7 , without needing to have a sharp tip in the vicinity of the examined structure. Because the interaction distance for the signal can be much larger than the diameter o