Intrinsic photoanode band engineering: enhanced solar water splitting efficiency mediated by surface segregation in Ti-doped hematite nanorods

Band engineering is thoroughly employed nowadays targeting technologically scalable photoanodes for solar water splitting applications. Most often complex and costly recipes are necessary, for average performances. Here we report very simple photoanode growth and thermal annealing, with effective band engineering results. Strongly enhanced photocurrent, of more than 200 %, is measured for Ti-doped hematite nanorods grown from aqueous solutions and annealed under Nitrogen atmosphere, compared to air annealed ones. Oxidized surface states and increased density of charge carriers are found responsible for the enhanced photoelectrochemical activity, as shown by electrochemical impedance spectroscopy and synchrotron X-rays spectromicroscopies. They are found related to oxygen vacancies, acting as n-dopants, and the formation of pseudo- brookite clusters by surface Ti segregation. Spectro-ptychography is used for the first time at Ti L3 absorption edge to isolate Ti chemical coordination arising from pseudo-brookite clusters contribution. Correlated with electron microscopy investigation and Density Functional Theory (DFT) calculations, our data unambiguously prove the origin of the enhanced photoelectrochemical activity of N2-annealed Ti-doped hematite nanorods. Finally, we present here a handy and cheap surface engineering method beyond the known oxygen vacancy doping, allowing a net gain in the photoelectrochemical activity for the hematite-based photoanodes.Comment: 2 parts: first main manuscript with 39 pages, second supplementary informations with 14 page

Local electronic structure and photoelectrochemical activity of partial chemically etched Ti-doped hematite

International audienceThe direct conversion of solar light into chemical energy or fuel through photoelectrochemical water splitting is promising as a clean hydrogen production solution. Ti-doped hematite (Ti:α-Fe 2 O 3) is a potential key photoanode material, which despite its optimal band gap, excellent chemical stability, abundance, non-toxicity and low cost, still has to be improved. Here we give evidence of a drastic improvement of the water splitting performances of Ti-doped hematite photoanodes upon a HCl wet-etching. In addition to the topography investigation by atomic force microscopy, a detailed determination of the local electronic structure has been carried out in order to understand the phenomenon and to provide new insights in the understanding of solar water splitting. Using synchrotron radiation based spectromicroscopy (X-PEEM), we investigated the X-ray absorption spectral features at the L 3 Fe edge of the as grown surface and of the wet-etched surface on the very same sample thanks to patterning. We show that HCl wet etching leads to substantial surface modifications of the oxide layer including increased roughness and chemical reduction (presence of Fe 2+) without changing the band gap. We demonstrate that these changes are profitable and correlated to the drastic changes of the photocatalytic activity

Double stripe ordering in Nd0.5Sr0.5MnO3 determined by resonant soft x-ray scattering

7 pages, 8 figures.-- PACS number(s): 75.47.Lx, 78.70.Ck, 71.30.+hWe have studied the low-temperature ordered phase of Nd0.5Sr0.5MnO3 by resonant soft x-ray scattering at the Mn L2,3 edges. Strong resonances were observed at (0 0) and ( 0 0) reflections, which are resolved in momentum space. Azimuthal scans reveal a periodicity for both resonances, the minimum intensity being almost zero. The two reflections show a very different energy dependence which extends in the whole energy region of the Mn L-edge. The (0 0) reflection originates from the anisotropy induced on the d-symmetry projected density of states owing to the local tetragonal distortion at one of the two crystallographic inequivalent Mn sites (the so-called Mn3+ ions in the conventional ionic description). This is similar to the resonance observed at the Mn K edge. We propose that the ( 0 0) reflection, which has not its counterpart either on the Mn K-edge resonant scattering or on the magnetic scattering, is originated by anisotropy of the d-symmetry projected density of the so-called Mn4+ sublattice. In this way, the latter reflection could denote a pure orbital ordering in this sublattice.We are thankful for the financial support from the Spanish CICyT Project No. MAT2005-04562 and from D.G.A. We also acknowledge ESRF and ID08 beamline for granting beam time.Peer reviewe

Soft X-ray spectro-ptychography on boron nitride nanotubes, carbon nanotubes and permalloy nanorods

Spectro-ptychography offers improved spatial resolution and additional phase spectral information relative to that provided by scanning transmission X-ray microscopes (STXM). However, carrying out ptychography at the lower range of soft X-ray energies (e.g., below 200 eV to 600 eV) on samples with weakly scattering signals can be challenging. We present soft X-ray ptychography results at energies as low as 180 eV and illustrate the capabilities with results from permalloy nanorods (Fe 2p), carbon nanotubes (C 1s), and boron nitride bamboo nanostructures (B 1s, N1s). We describe optimization of low energy X-ray spectro-ptychography and discuss important challenges associated with measurement approaches, reconstruction algorithms, and their effects on the reconstructed images. A method for evaluating the increase in radiation dose when using overlapping sampling is presented.Comment: 32 pages, 7 figure

THE COROLOGY, ECOLOGY AND PHYTOSOCIOLOGY OF THE WOODY PLANT COMMUNITIES OF THE LAPUŞNIC VALLEY, PART OF THE NERA GORGES-BEUŞNIŢA NATIONAL PARK

The examined area, process which started in 2011, is situated along the course of Lăpuşnic, a tributary of the Nera river and is an integral part of the Nera Gorges-Beuşniţa National Park. Calcareous substratum and climate influences sub-Mediterranean determine the type of flora and vegetation of Lăpuşnic Valley. In the Lăpuşnic basin there were identified numerous vulnerable (V), rare (R), and endangered (E) taxa, which are found in the red lists, published in our country. The general aspect of vegetation in the the Lăpuşnic basin represents an image of the very different stationary conditions, to which one can add the influence of the anthropo-zoogenous factors. The wooden vegetation is represented by forests, underwoods and riverside coppices, the forests occupy the largest area. In the Lăpuşnic basin, important areas are occupied by the beech forests belonging to the Festuco drymeiae-Fagetum Morariu et al. 1968 plant community. At lower altitudes, one can find alder tree groves which belong to the association Stellario nemori-Alnetum glutinosae (Kärstner 1938) Lohm. 1957. The Quercetum petraeae-cerris Sóo (1957) 1969 plant community grow on the slopes of the lower limit of the basin Lăpuşnic. Subcontinental peri-Pannonic scrub are represented by the following plant communities: Syringo-Fraxinetum orni Borza 1958 em. Resmeriţă 1972 (Syn.: Syringeto-Fraxinetum orni coryletosum colurnae Borza 1958; Syrigo-Carpinetum orientalis humiletosum domogledicum Jakucs 1959; Syringetum-Cotinetetum-Acaerineum tatarici Georgescu 1934), Cotino-Carpinetum orientalis Csürüs et al. -1968, Syringo-Carpinetum orientalis Jakucs 1959. They form the so called ,,sibliacuri,, and are included in the Habitat 40A0* - Subcontinental peri-Pannonic scrub. This plant communities are installed on bedrock, hard to reach land, with slopes moderately to highly pitched, even on steep walls

DIVERSITY, DISTRIBUTION AND ECOLOGY OF THE DACIAN BEECH FORESTS IN THE ŞUŞARA VALLEY- PART OF THE NERA GORGES BEUŞNIŢA NATIONAL PARK

The examined area, process which started in 2011, is situated along the course of Şuşara, a tributary of the Nera river and is an integral part of the Nera Gorges-Beuşniţa National Park. The wooden vegetation is represented by forests, underwoods and riverside coppices, the forests occupy the largest area. In the Şuşara basin, important areas are occupied by the beech forests belonging to the Phyllitidi – Fagetum Soó 1964 plant community. A new infra-coenotaxon was described: Phyllitidi – Fagetum Soó 1964 rusconetosum hypoglossae nova subass.Several types of analysis concerning the ecological features, the local distribution, the homogeneity (by using the Bray-Curtis dissimilarity index), the floristic composition and the economic importance were performed for this plant community

Reducing cardiovascular burden in psoriasis patients by using specific therapies – How close are we?

Psoriasis is a chronic, systemic inflammatory disease that has gained popularity among scientific research from many promising perspectives on diagnosis and treatment. Individuals with psoriasis associate numerous comorbidities and have many predisposing factors in common especially with heart disease. Based on this, researchers tried to identify the common pathogenic mechanisms, the impact of risk factors on both pathologies, the influence of one disease on the another as well as the impact of novel therapies used in psoriasis on cardiovascular system, in order to improve the prognosis and quality of life of these patients. Areas of uncertainty. Pathogenic mechanisms involved both in psoriasis and atherosclerotic disease are not fully understood, especially in relationship with actual treatment strategies and their impact on prognosis. The purpose of this descriptive review is to summarize the latest available data, to see whether current treatment strategies of psoriatic disease should take into consideration the risk of cardiovascular disease (CVD) when one drug should be chosen at the expense of another. Data sources. Literature research was performed using electronic database (PubMed, Cochrane Library and Web of Science) between January 2010 and June 2022. We used different keywords and MeSH terms to generate the most relevant results regarding psoriasis and cardiovascular disease. First, we evaluated the titles and abstracts of the articles and we excluded papers that didn’t met selection criteria

Search for dark matter produced in association with bottom or top quarks in √s = 13 TeV pp collisions with the ATLAS detector

A search for weakly interacting massive particle dark matter produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and miss- ing transverse momentum are considered. The analysis uses 36.1 fb−1 of proton–proton collision data recorded by the ATLAS experiment at √s = 13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are in- terpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour- neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross- section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour- charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements