Reflectance anisotropy spectroscopy of strain-engineered GaAsBi alloys

In this paper, we present results obtained by an optical technique, namely, reflectance anisotropy spectroscopy (RAS), applied to a series of GaAs1-xBix samples grown by molecular beam epitaxy (MBE) under different strain conditions with the increasing concentration of Bi, up to the higher value of about 7%. The epitaxial buffer layers for the growing GaAs1-xBix layer were prepared with either a compressive strain (as it is commonly done) or a tensile strain: The latter case has been proven to be a strategy that allows us to obtain a better crystalline quality [Tisbi et al., Phys. Rev. Appl. 14, 014028 (2020)]. A characteristic, well defined anisotropy signal below 2.5 eV is demonstrated to be connected to the presence of Bi and, in particular, to the strain produced in the sub-surface region by the voluminous Bi atoms. The amplitude of this signal directly relates to the Bi quantity, while its sign gives information about the local clustering/ordering of Bi atoms in the grown sample. We conclude that the detailed interpretation of RAS signatures and the knowledge of their origin offer the opportunity to utilize this technique to follow in real time the GaAsBi growth either in MBE or in metal organic vapor phase epitaxy processes

Peripheral neurological disturbances, autonomic dysfunction, and antineuronal antibodies in adult celiac disease before and after a gluten-free diet

Thirty-two consecutive adult celiac disease (CD) patients (pts), complaining of peripheral neuropathy (12 pts), autonomic dysfunction (17 pts), or both (3 pts), were evaluated to assess the presence of neurological damage (by clinical neurological evaluation and electrophysiological study) and antineuronal antibodies and to assess the effect of a gluten-free diet (GFD) on the course of the neurological symptoms and on antineuronal antibodies. At entry, 12 of 32 (38%) pts showed signs and symptoms of neurological damage: 7 of 12 (58%), peripheral neurological damage; 3 of 12 (25%), autonomic dysfunction; and 2 (17%), both peripheral neurological damage and autonomic dysfunction. The overall TNS score was 105 at entry. Anti-GM1 antibodies were present in 5 of 12 (42%) pts: 3 showed peripheral neurological damage and 2 showed both peripheral neurological damage and autonomic dysfunction. One year after the GFD was started, histological lesions were still present in only 10 of 12 (83%) pts. TNS score was 99, 98, 98, and 101 at the 3rd, 6th, 9th, and 12th month after the GFD was started, so it did not improve throughout the follow-up. None of the pts showed disappearance of antineuronal antibodies throughout the follow-up. We conclude that adult CD patients may show neurological damage and presence of antineuronal antibodies. Unfortunately, these findings do not disappear with a GFD

Exchange current density as an effective descriptor of poisoning of active sites in platinum group metal-free electrocatalysts for oxygen reduction reaction

The oxygen reduction reaction (ORR) is of primary importance for the direct and clean conversion of energy in fuel cells, necessarily requiring an electrocatalyst to be exploited. At the state of the art, platinum group metal-free (PGM-free) electrocatalysts are the most promising alternative to carbon-supported Pt nanoparticles (Pt/C), which are more expensive and more performing but highly prone to deactivation in a contaminated working environment. The comparison of the two materials is at the level of fine-tuning, requiring specific activity descriptors, namely, turnover frequency (TOF) and site density (SD), to understand how to compare the performance of PGM-free electrocatalysts with Pt/C electrocatalysts. Specific probing molecules that bind with the active sites are required to evaluate the SD of PGM-free electrocatalysts. However, PGM-free electrocatalysts possess not a single active site like Pt/C, but a multitude of primary (metal-containing) and secondary (metal-free) sites arising from the pyrolysis synthesis process, eventually complicating SD evaluation. In this work, we propose a method for evaluating the direct interaction through the chemisorption of probing molecules over the PGM-free primary and secondary sites, the discrimination of which is of paramount importance in an effective SD evaluation. Based on the rotating disk electrode technique, the study investigates the electrochemistry of Fe-based PGM-free electrocatalysts poisoned with hydrogen sulfide at pH 1 in comparison with a Pt/C sample. In addition, X-ray photoelectron spectroscopy (XPS) is used to establish a relationship between the electrochemistry and surface chemistry of the poisoned material. The results identify the exchange current density as a meaningful tool that allows the discrimination of poisoning of specific active sites (metal-containing or metal-free). In addition, the understanding of the interaction phenomenon occurring between sites and probing molecules will be paramount for the selection of those contaminants capable of selectively interacting with the active sites of interest, paving the way to a more accurate SD evaluation

Role of interfaces on the stability and electrical properties of Ge2Sb2Te5 crystalline structures

GeSbTe-based materials exhibit multiple crystalline phases, from disordered rocksalt, to rocksalt with ordered vacancy layers, and to the stable trigonal phase. In this paper we investigate the role of the interfaces on the structural and electrical properties of Ge2Sb2Te5. We find that the site of nucleation of the metastable rocksalt phase is crucial in determining the evolution towards vacancy ordering and the stable phase. By properly choosing the substrate and the capping layers, nucleation sites engineering can be obtained, thus promoting or preventing the vacancy ordering in the rocksalt structure or the conversion into the trigonal phase. The vacancy ordering occurs at lower annealing temperatures (170 °C) for films deposited in the amorphous phase on silicon (111), compared to the case of SiO2 substrate (200 °C), or in presence of a capping layer (330 °C). The mechanisms governing the nucleation have been explained in terms of interfacial energies. Resistance variations of about one order of magnitude have been measured upon transition from the disordered to the ordered rocksalt structure and then to the trigonal phase. The possibility to control the formation of the crystalline phases characterized by marked resistivity contrast is of fundamental relevance for the development of multilevel phase change data storage

Gender budgeting from a capability approach perspective: evidences from Senegal

The capability approach has been extensively used to measure wellbeing recognizing its complexity and the interaction of different dimensions of well-being. Its setting with a focus on the individual and his/her agency in the construction of well-being without being subsumed within the family, makes it suitable to measure well-being in a gender perspective and it is at the basis of well-being gender budgeting (GBwb). The objective of this paper is to show how the application of the capability approach to gender budgeting can lead to policies that are more effective in improving well-being and gender equity. The case study is the analysis of the forecast 2017 budget of the Municipality of Kaolack and its impact on education and health. Context analysis is carried out by using qualitative and quantitative data. Context analysis shows a high degree of deprivation in health and education achievements especially for girls and women. Budget analysis detects programmes that are directly or indirectly related to the development of the two dimensions and policies suggestions are provided. The paper shows that GBwb can help policymakers to better finetune policies in order to reduce gender inequalities and lead to better achievements in well-being