Computational and experimental studies of diffusion in monoclinic HfO2

Research on hafnia and zirconia has received a boost in the last two decades, mainly because of their electrical properties. As materials with high dielectric permittivity and a wide band-gap, they can replace SiO2 in Si-based semiconductor devices as the gate dielectric, and they can be employed as the insulator in metal—insulator—metal structures, showing memristive behavior.[1,2] Anion, and possibly cation, transport is of fundamental importance for the annealing of such devices and the proposed mechanism of resistive switching (filament switching in the case of HfO2).[2,3] In this study, we investigated both cation and anion diffusion in HfO2 using diffusion experiments, with subsequent determination of the diffusion profiles by Secondary Ion Mass Spectrometry (SIMS). For the diffusion of oxygen in dense ceramics of monoclinic HfO2,, (18O/16O) isotope exchange anneals were performed in the temperature range 573 ≤ T / K ≤ 973 at an oxygen partial pressure of pO2 = 200 mbar.[4] All measured isotope profiles exhibited two features: the first feature, closer to the surface, was attributed to slow oxygen diffusion in an impurity silicate phase; the second feature, deeper in the sample, was attributed to oxygen diffusion in a homogeneous bulk phase. The activation enthalpy of oxygen tracer diffusion in bulk HfO2 was found to be ΔHD* ≈ 0.5 eV. In contrast to oxygen diffusion, diffusion of cations in HfO2 and other oxide-ion conductors is experimentally much more challenging. It is slow, requiring, therefore, high temperatures and long diffusion times. In the case of HfO2, there is also the problem of Si impurities (see above), which are hard to get rid of in ceramic samples. To alleviate these problems somewhat, we directly investigated the diffusion of Zr in thin films of nanocrystalline, monoclinic HfO2, prepared by Atomic Layer Deposition (ALD) and coupled with a sputtered top layer of ZrO2 as a diffusion source. Diffusion experiments were performed in the temperature range 1173 ≤ T / K ≤ 1323 in air. All measured diffusion profiles exhibited bulk diffusion and fast grain-boundary diffusion. Using numerical simulations, we were able to describe the profiles and extract diffusion coefficients for Zr diffusion in bulk HfO2 and along its grain boundaries. The activation enthalpies of diffusion in both cases were, surprisingly, the same at ΔHDb/Dgb ≈ 2.1 eV. They are also much lower than activation energies predicted by static atomistic simulations.[5] In order to aid the interpretation of the experimental data, we conducted atomistic simulations of cation diffusion in HfO2. Specifically we performed Molecular Dynamics (MD) simulations using the empirical pair potentials derived by Catlow and Lewis.[6,7] These potentials are suitable for describing defect behaviour in HfO2.[8,9] The activation enthalpy of Hf diffusion in bulk HfO2 we obtained from the MD simulations agrees exceedingly well with the experimental results: ΔHD* ≈ 2 eV. The reasons for this behaviour are discussed. [1]: V. A. Gritsenko et al., Phys. Rep 613, 1 (2016). [2]: R. Waser et al., Adv. Mater. 21, 2632 (2009). [3]: S. Uhlenbruck et al., Solid State Ionics 180, 418 (2009). [4]: M. P. Mueller, R. A. De Souza, Appl. Phys. Lett. 112, 051908 (2018). [5]: S. Beschnitt et al., J. Phys. Chem. C 119, 27307 (2015). [6]: C. R. A. Catlow, Proc. R. Soc. Lond. A. 353(1675), 533 (1977). [7]: G. Lewis, C. R. A. Catlow, J. Phys. C: Solid State Phys. 18(6), 1149 (1985). [8]: M. Schie et al., J. Chem. Phys. 146, 094508 (2017). [9]: M. Schie et al., Phys. Rev. Mat. 2, 035002 (2018

Facial onset sensory and motor neuronopathy: new cases, cognitive changes and pathophysiology

Purpose of review To improve our clinical understanding of facial onset sensory and motor neuronopathy (FOSMN). Recent findings We identified 29 new cases and 71 literature cases, resulting in a cohort of 100 patients with FOSMN. During follow-up, cognitive and behavioral changes became apparent in 8 patients, suggesting that changes within the spectrum of frontotemporal dementia (FTD) are a part of the natural history of FOSMN. Another new finding was chorea, seen in 6 cases. Despite reports of autoantibodies, there is no consistent evidence to suggest an autoimmune pathogenesis. Four of 6 autopsies had TAR DNA-binding protein (TDP) 43 pathology. Seven cases had genetic mutations associated with neurodegenerative diseases. Summary FOSMN is a rare disease with a highly characteristic onset and pattern of disease progression involving initial sensory disturbances, followed by bulbar weakness with a cranial to caudal spread of pathology. Although not conclusive, the balance of evidence suggests that FOSMN is most likely to be a TDP-43 proteinopathy within the amyotrophic lateral sclerosis–FTD spectrum

C-reactive protein is essential for innate resistance to pneumococcal infection

Summary: No deficiency of human C-reactive protein (CRP), or even structural polymorphism of the protein, has yet been reported so its physiological role is not known. Here we show for the first time that CRP-deficient mice are remarkably susceptible to Streptococcus pneumoniae infection and are protected by reconstitution with isolated pure human CRP, or by anti-pneumococcal antibodies. Autologous mouse CRP is evidently essential for innate resistance to pneumococcal infection before antibodies are produced. Our findings are consistent with the significant association between clinical pneumococcal infection and non-coding human CRP gene polymorphisms which affect CRP expression. Deficiency or loss of function variation in CRP may therefore be lethal at the first early-life encounter with this ubiquitous virulent pathogen, explaining the invariant presence and structure of CRP in human adults

Avaliação do impacto do curso de cromatografia: a experiência de adaptação e aplicação de um instrumento em profundidade e em largura para as capacitações on-line da Embrapa.

Este artigo apresenta a experiência da Embrapa com a adaptação e aplicação de um instrumento de avaliação de impacto em profundidade e em largura das capacitações on-line ofertadas ao seu público externo, detalhando os resultados obtidos para o curso de Cromatografia. Na revisão da literatura destaca-se o modelo ADDIE e a importância da avaliação de impacto para o processo. Na sequência é apresentado como foi a construção e aplicação do instrumento, seguidos da análise dos resultados e considerações finais. A pesquisa permitiu verificar que a oferta do curso de Cromatografia no formato on-line autoinstrucional e assíncrono, além de promover a democratização do acesso ao conhecimento, também obteve ótimos níveis de impacto em situações reais de trabalho. Os resultados reforçam a importância da aplicação de instrumentos de avaliação de impacto como uma ação contínua e sistemática de qualquer programa de capacitação e também evidenciam a necessidade de se aprimorar a qualidade das etapas precedentes, especialmente do desenho instrucional da capacitação. Abstract. This article presents 's experience with the adaptation and application of an instrument to evaluate in depth and breadth the impact of the online training offered to its external public, detailing the results obtained for the Chromatography course. The literature review highlights the ADDIE model adopted by , 's online training showcase, and the importance of impact assessment for the process. In the sequence, it is presented how the construction and application of the instrument was, followed by the analysis of the results and final considerations. The research made it possible to verify that the offer of the Chromatography course in the self-instructional and asynchronous online format, in addition to promoting the democratization of access to knowledge, also achieved excellent levels of impact in real work situations. The results reinforce the importance of applying impact assessment instruments as a continuous and systematic action of any training program and also highlight the need to improve the quality of the preceding stages, especially the instructional design of the training.Na publicaçã

Multiferroicity in an organic charge-transfer salt: Electric-dipole-driven magnetism

Multiferroics, showing simultaneous ordering of electrical and magnetic degrees of freedom, are remarkable materials as seen from both the academic and technological points of view. A prominent mechanism of multiferroicity is the spin-driven ferroelectricity, often found in frustrated antiferromagnets with helical spin order. There, similar to conventional ferroelectrics, the electrical dipoles arise from an off-centre displacement of ions. However, recently a different mechanism, namely purely electronic ferroelectricity, where charge order breaks inversion symmetry, has attracted considerable interest. Here we provide evidence for this exotic type of ferroelectricity, accompanied by antiferromagnetic spin order, in a two-dimensional organic charge-transfer salt, thus representing a new class of multiferroics. Quite unexpectedly for electronic ferroelectrics, dipolar and spin order arise nearly simultaneously. This can be ascribed to the loss of spin frustration induced by the ferroelectric ordering. Hence, here the spin order is driven by the ferroelectricity, in marked contrast to the spin-driven ferroelectricity in helical magnets.Comment: 8 pages, 9 figures (including 4 pages and 6 figures in supplementary information). Version 2 with minor errors corrected (legend of Fig. 3c and definition of vectors e and Q

A search for point sources of EeV photons

Measurements of air showers made using the hybrid technique developed with the fluorescence and surface detectors of the Pierre Auger Observatory allow a sensitive search for point sources of EeV photons anywhere in the exposed sky. A multivariate analysis reduces the background of hadronic cosmic rays. The search is sensitive to a declination band from -85{\deg} to +20{\deg}, in an energy range from 10^17.3 eV to 10^18.5 eV. No photon point source has been detected. An upper limit on the photon flux has been derived for every direction. The mean value of the energy flux limit that results from this, assuming a photon spectral index of -2, is 0.06 eV cm^-2 s^-1, and no celestial direction exceeds 0.25 eV cm^-2 s^-1. These upper limits constrain scenarios in which EeV cosmic ray protons are emitted by non-transient sources in the Galaxy.Comment: 28 pages, 10 figures, accepted for publication in The Astrophysical Journa

Reconstruction of inclined air showers detected with the Pierre Auger Observatory

We describe the method devised to reconstruct inclined cosmic-ray air showers with zenith angles greater than $60^\circ$ detected with the surface array of the Pierre Auger Observatory. The measured signals at the ground level are fitted to muon density distributions predicted with atmospheric cascade models to obtain the relative shower size as an overall normalization parameter. The method is evaluated using simulated showers to test its performance. The energy of the cosmic rays is calibrated using a sub-sample of events reconstructed with both the fluorescence and surface array techniques. The reconstruction method described here provides the basis of complementary analyses including an independent measurement of the energy spectrum of ultra-high energy cosmic rays using very inclined events collected by the Pierre Auger Observatory.Comment: 27 pages, 19 figures, accepted for publication in Journal of Cosmology and Astroparticle Physics (JCAP

Highlights from the Pierre Auger Observatory

The Pierre Auger Observatory is the world's largest cosmic ray observatory. Our current exposure reaches nearly 40,000 km$^2$ str and provides us with an unprecedented quality data set. The performance and stability of the detectors and their enhancements are described. Data analyses have led to a number of major breakthroughs. Among these we discuss the energy spectrum and the searches for large-scale anisotropies. We present analyses of our X$_{max}$ data and show how it can be interpreted in terms of mass composition. We also describe some new analyses that extract mass sensitive parameters from the 100% duty cycle SD data. A coherent interpretation of all these recent results opens new directions. The consequences regarding the cosmic ray composition and the properties of UHECR sources are briefly discussed.Comment: 9 pages, 12 figures, talk given at the 33rd International Cosmic Ray Conference, Rio de Janeiro 201

Measurement of the Depth of Maximum of Extensive Air Showers above 10^18 eV

We describe the measurement of the depth of maximum, Xmax, of the longitudinal development of air showers induced by cosmic rays. Almost four thousand events above 10^18 eV observed by the fluorescence detector of the Pierre Auger Observatory in coincidence with at least one surface detector station are selected for the analysis. The average shower maximum was found to evolve with energy at a rate of (106 +35/-21) g/cm^2/decade below 10^(18.24 +/- 0.05) eV and (24 +/- 3) g/cm^2/decade above this energy. The measured shower-to-shower fluctuations decrease from about 55 to 26 g/cm^2. The interpretation of these results in terms of the cosmic ray mass composition is briefly discussed.Comment: Accepted for publication by PR