Downshift of the Ni d band center over Ni nanoparticles in situ confined within an amorphous silicon nitride matrix

Herein, nanocomposites made of Ni nanoparticles in situ distributed in an amorphous silicon nitride (Ni/a-Si3N4) matrix, on the one hand, and within an amorphous silicon dioxide (Ni/a-SiO2) matrix, on the other hand, were synthesized from the same Ni-modified polysilazane precursor. In both compounds, the Ni/Si atomic ratio (0.06-0.07), average Ni nanocrystallite size (7.0-7.6 nm) and micro/mesoporosity of the matrix were rigorously fixed. Hydrogen (H2)-temperature-programmed desorption (TPD) profile analysis revealed that the activation energy for H2 desorption at about 100-130 °C evaluated for the Ni/a-Si3N4 sample (47.4 kJ mol-1) was lower than that for the Ni/a-SiO2 sample (68.0 kJ mol-1). Mechanistic study with X-ray photoelectron spectroscopy (XPS) analysis and density functional theory (DFT) calculations revealed that, at Ni nanoparticle/matrix heterointerfaces, Ni becomes more covalently bonded to N atoms in the a-Si3N4 matrix compared to O atoms in the a-SiO2 matrix. Therefore, based on experimental and theoretical studies, we elucidated that nickel-nitrogen (Ni-N) interactions at the heterointerface lead to remarkable Ni d band broadening and downshifting of the d band center relative to those generated by Ni-oxygen (Ni-O) interactions at the heterointerface. This facilitates H2 desorption, as experimentally observed in the Ni/a-Si3N4 sample.

Defect engineering of 1T'MX2(M= Mo, W andX= S, Se) transition metal dichalcogenide-based electrocatalyst for alkaline hydrogen evolution reaction

The alkaline electrolyzer (AEL) is a promising device for green hydrogen production. However, their energy conversion efficiency is currently limited by the low performance of the electrocatalysts for the hydrogen evolution reaction (HER). As such, the electrocatalyst design for the high-performance HER becomes essential for the advancement of AELs. In this work, we used both hydrogen (H) and hydroxyl (OH) adsorption Gibbs free energy changes as the descriptors to investigate the catalytic HER performance of 1T' transition metal dichalcogenides (TMDs) in an alkaline solution. Our results reveal that the pristine sulfides showed better alkaline HER performance than their selenide counterparts. However, the activities of all pristine 1T' TMDs are too low to dissociate water. To improve the performance of these materials, defect engineering techniques were used to design TMD-based electrocatalysts for effective HER activity. Our density functional theory results demonstrate that introducing single S/Se vacancy defects can improve the reactivities of TMD materials. Yet, the desorption of OH becomes the rate-determining step. Doping defective MoS2with late 3d transition metal (TM) atoms, especially Cu, Ni, and Co, can regulate the reactivity of active sites for optimal OH desorption. As a result, the TM-doped defective 1T' MoS2can significantly enhance the alkaline HER performance. These findings highlight the potential of defect engineering technologies for the design of TMD-based alkaline HER electrocatalysts.

Impact of the local atomic structure on the thermal conductivity of amorphous Ge2Sb2Te5

Thermal properties are expected to be sensitive to the network topology, and however, no clearcut information is available on how the thermal conductivity of amorphous systems is affected by details of the atomic structure. To address this issue, we use as a target system a phase-change amorphous material (i.e., Ge₂Sb₂Te₅) simulated by first-principles molecular dynamics combined with the approach-to-equilibrium molecular dynamics technique to access the thermal conductivity. Within the density-functional theory, we employed two models sharing the same exchange-correlation functional but differing in the pseudopotential (PP) implementation [namely, Trouiller-Martins (TM) and Goedecker, Teter, and Hutter (GTH)]. They are both compatible with experimental data, and however, the TM PP construction results in a Ge tetrahedral environment largely predominant over the octahedral one, although the proportion of tetrahedra is considerably smaller when the GTH PP is used. We show that the difference in the local structure between TM and GTH models impacts the vibrational density of states while the thermal conductivity does not feature any appreciable sensitivity to such details. This behavior is rationalized in terms of extended vibrational modes.

Low temperature in situ immobilization of nanoscale fcc and hcp polymorphic nickel particles in polymer-derived Si-C-O-N(H) to promote electrocatalytic water oxidation in alkaline media

We synthesized nickel (Ni) nanoparticles (NPs) in a high specific surface area (SSA) p-block element-containing inorganic compound prepared via the polymer-derived ceramics (PDC) route to dispatch the obtained nanocomposite towards oxygen evolution reaction (OER). The in situ formation of Ni NPs in an amorphous silicon carboxynitride (Si-C-O-N(H)) matrix is allowed by the reactive blending of a polysilazane, NiCl₂ and DMF followed by the subsequent thermolysis of the Ni : organosilicon polymer coordination complex at a temperature as low as 500 °C in flowing argon. The final nanocomposite displays a BET SSA as high as 311 m² g^-1 while the structure of the NPs corresponds to face-centred cubic (fcc) Ni along with interstitial-atom free (IAF) hexagonal close-packed (hcp) Ni as revealed by XRD. A closer look into the compound through FEG-SEM microscopy confirms the formation of pure metallic Ni, while HR-TEM imaging reveals the occurrence of Ni particles featuring a fcc phase and surrounded by carbon layers; thus, forming core-shell structures, along with Ni NPs in an IAF hcp phase. By considering that this newly synthesized material contains only Ni without doping (e.g., Fe) with a low mass loading (0.15 mg cm^-2), it shows promising OER performances with an overpotential as low as 360 mV at 10 mA cm^-2 according to the high SSA matrix, the presence of the IAF hcp Ni NPs and the development of core-shell structures. Given the simplicity, the flexibility, and the low cost of the proposed synthesis approach, this work opens the doors towards a new family of very active and stable high SSA nanocomposites made by the PDC route containing well dispersed and accessible non-noble transition metals for electrocatalysis applications.

New and refined bond valence parameters for Te4+–F−, Te4+–S2− and Te4+–Se2− ion pairs

New and refined bond valence parameters related to ion pairs constituted of the tellurium Te4+ cation and non-oxide X n− anions (X = F, S or Se) are proposed. After a selection of specific crystalline structures, the optimization of the bond valence parameters R and b with a cutoff distance is carried out by minimizing the root mean square deviation of the Te4+ cation valence. The results are R = 1.728 Å and b = 0.622 Å with cutoff = 5.3 Å for the Te4+–F− pair and R = 2.444 Å and b = 0.387 Å with cutoff = 4.5 Å for the Te4+–S2− pair. These parameters lead to a lower dispersion of the calculated valences around the formal valence compared to that obtained with the parameters available in the literature. As for the new set related to the Te4+–Se2− pair, we find R = 2.578 Å and b = 0.296 Å with cutoff = 3.7 Å.

Evolution of anti-SARS-CoV-2 immune response in a cohort of French healthcare workers followed for 7 months

Objectives

We aimed to understand the immune response among healthcare workers (HCWs) following SARS-CoV-2 infection, and to determine the infection prevalence during the first wave of the pandemic among workers in our hospital.

Methods

Determination of the serological status against SARS-CoV-2 (nucleocapsid) was offered to all HCWs. All HCWs with positive SARS-CoV-2 serology were proposed to be included in a longitudinal medical and serological follow-up (anti-spike) for 7 months.

Results

We included 3062 HCWs; 256 (8.4%) were positive for anti-SARS-CoV-2 nucleocapsid IgG. Among them, early decrease in the anti-nucleocapsid antibody index was observed between the first (S1) and second (S2) serology samplings in 208 HCWs (84.2%). The initial anti-nucleocapsid IgG index seemed to be related to the HCWs’ age. Seventy-four HCWs were included in the 7-month cohort study. Among them, 69 (90.5%) had detectable anti-spike IgG after 7 months and 24 (32.4%) reported persistent symptoms consistent with post-acute COVID-19 syndrome diagnosis.

Conclusion

The prevalence of serological positivity among HCWs was 6.7%. Infection should be followed by vaccination because of antibody decrease.

First-principles thermal transport in amorphous Ge2Sb2Te5 at the nanoscale

Achieving a precise understanding of nanoscale thermal transport in phase change materials (PCMs), such as Ge2Sb2Te5 (GST), is the key of thermal management in nanoelectronics, photonic and neuromorphic applications using non-volatile memories. By resorting to a first-principles approach to calculate the thermal conductivity of amorphous GST, we found that size effects and heat transport via propagative modes persist well beyond extended range order distances typical of disordered network-forming materials. Values obtained are in quantitative agreement with the experimental data, by revealing a strong size dependence of the thermal conductivity down to the 1.7-10 nm range, fully covering the scale of current PCMs-based devices. In particular, a reduction of thermal conductivity as large as 75% occurs for dimensions lying below 2 nm. These results provide a quantitative description of the thermal properties of amorphous GST at the nanoscale and are expected to underpin the development of PCM-based device applications.

Atomic Structure of Glassy GeTe4 as a Playground to Assess the Performances of Density Functional Schemes Accounting for Dispersion Forces

The atomic structure of glassy GeTe₄ is obtained in the framework of first-principles molecular dynamics (FPMD) by considering five different approaches for the description of the electronic structure within density functional theory (DFT). Among these schemes, one is not corrected by accounting for the dispersion forces and it is based on the BLYP exchange-correlation (XC) functional, while all of the others consider the dispersion forces according to different theoretical strategies. In particular, by maintaining the BLYP expression for the XC functional, two of them (BLYP-D2 and BLYP-D3) exploit the Grimme expressions for the dispersion forces, while the fourth scheme is based on the maximally localized Wannier functions (MLWFs). Finally, we also considered the rVV10 functional constructed to include seamlessly the dispersion part. Our results point out the better performances of BLYP-D3 and MLWF in terms of comparison with experimental data for the total pair correlation functions, with BLYP-D2 and rVV10 being closer to the uncorrected BLYP data. The implications of such findings are discussed by considering the overall limited impact of dispersion forces on the atomic structure of glassy GeTe₄.

Short range order and network connectivity in amorphous AsTe3: a first principles, machine learning, and XRD study

The atomic scale structure of amorphous AsTe₃ is investigated through X-ray diffraction, first-principles molecular dynamics (FPMD), and machine learning interatomic potentials (ML-GAP) obtained by exploiting the ab initio data. We obtain good agreement between the measured and modelled diffraction patterns. Our FPMD results show that As and Te obey the 8-N rule with average coordination numbers of 3 and 2, respectively. We find that small fractions of under and over coordinated As and Te atoms are present in the amorphous phase with about 6% (FPMD), and 13% (ML-GAP) of 3-fold Te. As is found at the center of pyramidal structures predominantly linked through Te_n chains rather than rings. Despite the low As concentration in AsTe₃, its local environment features a very high chemical disorder that manifests through the occurrence of homopolar bonds including at least 57% of As atoms.

Oxide versus Nonoxide Cathode Materials for Aqueous Zn Batteries: An Insight into the Charge Storage Mechanism and Consequences Thereof

Aqueous Zn-ion batteries, which are being proposed as large-scale energy storage solutions because of their unparalleled safety and cost advantage, are composed of a positive host (cathode) material, a metallic zinc anode, and a mildly acidic aqueous electrolyte (pH ≈ 3-7). Typically, the charge storage mechanism is believed to be reversible Zn²⁺ (de)intercalation in the cathode host, with the exception of α-MnO₂, for which multiple vastly different and contradicting mechanisms have been proposed. However, our present study, combining electrochemical, operando X-ray diffraction, electron microscopy in conjunction with energy-dispersive X-ray spectroscopy, and in situ pH evolution analyses on two oxide hosts-tunneled α-MnO₂ and layered V₃O₇·H₂O vis-à-vis two nonoxide hosts-layered VS₂ and tunneled Zn₃[Fe(CN)₆]₂, suggests that oxides and nonoxides follow two dissimilar charge storage mechanisms. While the oxides behave as dominant proton intercalation materials, the nonoxides undergo exclusive zinc intercalation. Stabilization of H⁺ on the hydroxyl-terminated oxide surface is revealed to facilitate the proton intercalation by a preliminary molecular dynamics simulation study. Proton intercalation for both oxides leads to the precipitation of layered double hydroxide (LDH)-Zn₄SO₄(OH)₆·5H₂O with a ZnSO₄/H₂O electrolyte and a triflate anion (CF₃SO₃^-)-based LDH with a Zn(SO₃CF₃)₂/H₂O electrolyte-on the electrode surface. The LDH precipitation buffers the pH of the electrolytes to a mildly acidic value, sustaining the proton intercalation to deliver large specific capacities for the oxides. Moreover, we also show that the stability of the LDH precipitate is crucial for the rechargeability of the oxide cathodes, revealing a critical link between the charge storage mechanism and the performance of the oxide hosts in aqueous zinc batteries.

Atomic-Scale Simulation of Electrochemical Processes at Electrode/Water Interfaces under Referenced Bias Potential

Based on constant Fermi-level molecular dynamics and a proper alignment scheme, we perform simulations of the Pt(111)/water interface under variable bias potential referenced to the standard hydrogen electrode (SHE). Our scheme yields a potential of zero charge μ_pzc of ∼0.22 eV relative to the SHE and a double layer capacitance C_dl of ≃19 μF cm^-2, in excellent agreement with experimental measurements. In addition, we study the structural reorganization of the electrical double layer for bias potentials ranging from -0.92 eV to +0.44 eV and find that O_down configurations, which are dominant at potentials above the pzc, reorient to favor H_down configurations as the measured potential becomes negative. Our modeling scheme allows one to not only access atomic-scale processes at metal/water interfaces, but also to quantitatively estimate macroscopic electrochemical quantities.

Electron trap states at InGaAs/oxide interfaces under inversion through constant Fermi-level ab initio molecular dynamics

We employ constant-Fermi-level ab initio molecular dynamics to investigate defects at the InGaAs/oxide interface upon inversion. We adopt a substoichiometric amorphous model for modelling the structure at the interface and investigate the formation of defect structures upon setting the Fermi-level above the conduction band minimum. The defect formation is detected through both an analysis of the atomic structure and a Wannier-decomposition of the electronic structure. This computer driven approach is able to retrieve In and Ga lone-pair defects and As-As dimer/dangling bond defects, in agreement with previous studies based on physical intuition. In addition, the present simulation reveals hitherto unidentified defect structures consisting of metallic In-In, In-Ga, and Ga-Ga bonds. The defect charge transition levels of such metallic bonds in Al₂O₃ are then determined through a hybrid functional scheme and found to be consistent with the defect density measured at InGaAs/Al₂O₃ interfaces. Hence, we conclude that both In and Ga lone pairs dangling bonds and metallic In-In bonds are valid candidate defects for charge trapping at InGaAs/oxide interfaces upon charge carier inversion. This study demonstrates the effectiveness of constant-Fermi-level ab initio molecular dynamics in revealing and identifying defects at InGaAs/oxide interfaces.

Thermal conductivity of glassy GeTe4by first-principles molecular dynamics

A transient thermal regime is achieved in glassy GeTe₄by first-principles molecular dynamics following the recently proposed “approach-to-equilibrium” methodology.

[Feasibility and diagnostic value of hysterosonography performed in bleeding time in the exploration of abnormal uterine bleeding]

OBJECTIVES

The aim of our study is to evaluate the feasibility, safety and diagnostic value of hysterosonography performed in an emergency setting among patients consulting for active abnormal uterine bleeding.

MATERIALS AND METHODS

In this prospective study, we included 216 patients visiting our emergency department for abnormal uterine bleeding. All patients had a transvaginal ultrasound with doppler study and an hysterosonography. Secondly, the patients, in whom we diagnosed a suspected organic lesion, were addressed to an endoscopic or surgical procedure with pathological examination. Initially, we evaluated the feasibility and the safety of hysterosonography and secondly, we compared the two techniques (EEV and hysterosonography), sensitivity, specificity, LHR+and LHR-.

RESULTS

The hysterosonography was performed in 98.1 % of patients and its realization has resulted in an additional period of 1.2minutes on average (extreme: 6-12) compared to ultrasound. The tolerance of the hysterosonographic examination was very good in 73.5 % of patients and good in 23.1 % of them. For the 167 patients who had been diagnosed with presumed organic lesions, pathological examination found an endometrial hyperplasia in 34.7 % of cases, polyps in 40.1 % of cases, sub-mucosal fibroids in 11.3 % of cases, endometrial cancer in 0.7 % of cases and other lesions in 13.2 % of cases. The diagnostic value of hysterosonography was superior to ultrasound in the detection of polyps (AUC: 0.894 vs 0.778, P=0.003) and fibromas (AUC: 1.000 vs 0.716, P=0.001) while the two methods showed no significant difference in the detection of hyperplasia.

CONCLUSION

The purpose of our study was to focus on a particular context of use of the hysterosonography consisting on hemorrhagic period and on its realization in the emergency room. We were able to demonstrate that hysterosonography is compatible with the emergency situation as to its feasibility and its diagnostic value and that its realization would contribute to the sorting of patients to guide them immediately to a surgical or endoscopic procedure if necessary.

Origin of structural analogies and differences between the atomic structures of GeSe4 and GeS4 glasses: A first principles study

First-principles molecular dynamics simulations based on density functional theory are employed for a comparative study of structural and bonding properties of two stoichiometrically identical chalcogenide glasses, GeSe4 and GeS4. Two periodic cells of 120 and 480 atoms are adopted. Both glasses feature a coexistence of Ge-centered tetrahedra and Se(S) homopolar connections. Results obtained for N = 480 indicate substantial differences at the level of the Se(S) environment, since Ge-Se-Se connections are more frequent than the corresponding Ge-S-S ones. The presence of a more prominent first sharp diffraction peak in the total neutron structure factor of glassy GeS4 is rationalized in terms of a higher number of large size rings, accounting for extended Ge-Se correlations. Both the electronic density of states and appropriate electronic localization tools provide evidence of a higher ionic character of Ge-S bonds when compared to Ge-Se bonds. An interesting byproduct of these investigations is the occurrence of discernible size effects that affect structural motifs involving next nearest neighbor distances, when 120 or 480 atoms are used.

An experimental model of gastroschisis using fetoendoscopy: preliminary results and technical considerations

BACKGROUND

The aim of this study was to show the feasibility of an experimental model of gastroschisis using fetoendoscopic surgery on sheep fetuses, and also to perform amnioinfusion until delivery using an in-dwelling intraamniotic catheter.

METHODS

We analyzed the data from 18 pregnant ewes having 26 fetuses, which underwent surgery at 80 days of gestation (full term, 145 days). The fetendo technique was used to create a gastroschisis in 15 fetuses. The fetal abdominal wall was opened on the left side of the cord using scissors. The omentum and the intestinal loops were eviscerated using atraumatic forceps. Eleven fetuses were used as a control group. Twenty-one fetuses underwent amnioinfusion; a simple exteriorized catheter was used in seven cases and an intraamniotic catheter with an implantable port was used in the other 14. All ewes and fetuses were killed at the end of the experiment by an intravenous injection of pentotal; thereafter, the fetuses underwent necropsy.

RESULTS

Twelve fetuses died and 14 survived (53.8%); seven of the 15 that underwent gastroschisis survived (46.7%). An amniotic infection occurred in nine fetuses (34.6%); of these, six died and three that were administered antibiotics survived.

CONCLUSIONS

Our experience shows that this experimental model of gastroschisis is feasible and reproducible, and that a repeated amnioinfusion can be performed with an in-dwelling catheter in pregnant ewes. The use of an implantable port is safer than a simple exteriorized catheter.

Scattering analysis of slanted fiber gratings

The diffraction efficiency of a tilted in-core fiber grating is analyzed with the scattering formalism and the first Born approximation. Without any prior physical assumptions about the shape or direction of the scattered wave, it is shown that diffraction occurs when the so-called Bragg conditions are nearly satisfied and the interaction process can be described by a pair of coupled first-order differential equations that are exactly the same as those obtained through the coupled-mode analysis.

Measurement of the extensional and flexural rigidities of a subcellular structure: marginal bands isolated from erythrocytes of the newt

The elastic properties of marginal band, a microtubular structure isolated from the newt (notophthalmus viridescens) have been measured. Bands were isolated using Triton X-100 and pepsin at pH 6.8 according to the method of Cohen (1978). Isolated bands were manipulated with a glass microhook in a buffer-filled chamber under the microscope. Single bands were stretched between the hook and a thin glass fiber. The fiber was calibrated so that the force on the band could be calculated from the displacement of the fiber. The data pairs of force versus band deflection were analyzed according to the theoretical work of Libai and Simmonds (1983) to obtain the flexural and extensional rigidities of the band. Band dimensions calculated from the data were consistent with microscopically determined values. The average flexural rigidity of the bands (EI) was 5.3 X 10(-13) dyn X cm2 and the average extensional rigidity (EA) was 0.017 dyn. Compared to the cell membrane, the marginal band is nearly inextensible and has a much greater resistance to bending, indicating that the band makes an important contribution to the deformability of the circulating cell.