Time reversal symmetry breaking in the s wave superconductor CaPd2As2 probed by mu SR

CaPd2 amp; 8290;As2 is known to superconduct below amp; 119879; amp; 119888; 1.27 amp; 8290; 3 K. In this work we examine whether the time reversal symmetry TRS is preserved or broken upon entering the superconducting state in CaPd2 amp; 8290;As2, and probe its superconducting gap structure using muon spin relaxation and rotation amp; 120583; amp; 8290;SR measurements in zero field ZF and transverse field TF , respectively. The analysis of ZF amp; 120583; amp; 8290;SR spectra reveals an increase in muon spin relaxation rate amp; 120582;ZF in the superconducting SC state attesting the presence of a weak magnetic field. The appearance of spontaneous magnetic field indicates the breaking of time reversal symmetry state upon entering the SC state of CaPd2 amp; 8290;As2. The analysis of TF amp; 120583; amp; 8290;SR spectra provides information about the superconducting gap structure of CaPd2 amp; 8290;As2 which is found to have a single band isotropic amp; 119904; wave symmetry. We find an isotropic energy gap amp; 916; amp; 8289; 0 0.160 amp; 8290; 1 meV corresponding to 2 amp; 8290; amp; 916; amp; 8289; 0 amp; 119896;B amp; 8290; amp; 119879; amp; 119888; 3.37 amp; 8290; 3 which is close to the weak coupling BCS value of 3.53. The analysis of TF amp; 120583; amp; 8290;SR also provides an estimate of effective penetration depth which is found to be amp; 120582;eff amp; 8289; 0 415 amp; 8290; 16 nm. Our amp; 120583; amp; 8290;SR data thus find evidence for TRS breaking in CaPd2 amp; 8290;As2 with an amp; 119904; wave singlet paring which is not expected for a conventional superconducto

Electrostatic and Electronic Effects on Doped Nickel Oxide Nanofilms for Water Oxidation

An ideal water splitting electrocatalyst is inexpensive, abundant, highly active, stable, selective, and durable. The anodic oxygen evolution reaction OER is the main bottleneck for H2 production with a complex and not fully resolved mechanism, slow kinetics, and high overpotential. Nickel oxide based catalysts NiOx are highly active and cheaper than precious metal catalysts. However, rigorous catalyst tests and DFT calculations are still needed to rationally optimize NiOx catalysts. In this work, we combine plasma enhanced atomic layer deposition PE ALD and density functional theory DFT to address the role of dopants in promoting NiOx OER activity. Ultrathin films of NiOx doped with Zn2 , Al3 , and Sn4 presented improved intrinsic activity, stability, and durability for the OER. The results show a low to high catalytic performance of ZnNiOx lt; NiOx lt; AlNiOx lt; SnNiOx, which we attribute to an increase in the concentration of valence band VB holes combined with conduction band CB electron conductivity, characterized by electrochemical impedance spectroscopy EIS . The influence of doping on the electronic structure and catalytic activity was investigated using advanced characterization techniques and density functional theory DFT calculations PEB0 pob TZVP . DFT complements the experimental results, showing that the dopant charge states and orbital hybridization enhance the OER by improving the charge carrier concentration and mobility, thus allowing optimal binding energies and charge dynamics and delocalization. Our findings demonstrate the potential of PE ALD doped nanofilms NiOx and DFT to rationally design and develop catalysts for sustainable energy application

Importance of Electrostatic Effects for Interpretation of X ray Photoemission Spectra of Self Assembled Monolayers

This paper reviews the relevant work regarding electrostatic effects in X ray photoemission from self assembled monolayers SAMs which are application relevant ultrathin molecular films, coupled over a suitable anchoring group to the substrate. Whereas, in most cases, the standard concept of chemical shift is fully sufficient to describe X ray photoelectron spectra of these systems, consideration of electrostatic effects is frequently necessary for their proper interpretation. Due to the insulator character of the SAM matrix, decoupled electronically from the substrate, the introduction of a dipolar sheet at the SAM substrate interface or within this matrix creates a potential discontinuity shifting the energy levels above the sheet with respect to those below it. This shift is reflected then in the matrix related spectra, resulting in shifts and splitting of the characteristic photoemission peaks. Several representative examples in this context are provided and discussed in detail. These examples and other relevant literature data underline the importance of electrostatic effects in photoemission and suggest that they should be considered on the equal footing as the chemical shift one

In situ UV Vis absorption spectroscopy study of the water electrooxidation on cobalt oxide catalysts

Despite the current prominence of cobalt oxides as electrocatalysts for the alkaline oxygen evolution reaction OER , there is a lack of unambiguous demonstration for the presence and the role of Co4 prior to during the OER. Here, we combine electrochemistry with in situ UV Vis absorption spectroscopy to investigate and discuss the previously unaddressed effect of different OH amp; 8722; concentrations in the range from 1 M to 0.016 M on the population of Co4 in thin films of CoOx and its concomitant impact on their OER performance. Evidence for Co4 is provided by in situ X ray absorption spectroscopy. Our UV Vis absorption spectroscopic findings indicate that, not only can the overall redox conversion of Co be qualitatively monitored as a function of potential and OH amp; 8722; concentration, but also the formation of oxidized Co i.e.,Co3 and Co4 assigned to a peak at 800 nm can be more quantitatively tracked in situ via stepped potential spectroelectrochemistry; with their optical signals becoming stronger at higher OH amp; 8722; concentrations above 1.2 V vs. RHE, which is consistent with voltammetric redox couples, indicating an enhancement in Co oxidation state and the consequent predominance of Co4 under conditions of elevated OH amp; 8722; concentrations. Furthermore, the evolved oxygen due to OER does not depend on Co4 or OH amp; 8722; activity at 1.54 V vs. RHE, while a correlation with both Co4 and OH amp; 8722; is identified at 1.59 V vs. RHE. This study not only provides spectral insight into the redox chemistry of Co at OER relevant potentials but also highlights the importance of Co4 in facilitating the alkaline OER at high OH amp; 8722; concentrations and current densitie

R for Reactive Revealing Rhodium, Ruthenium, and Rhenium s Rare Oxides through X ray Absorption Spectroscopy

Discovering compounds that present transition metals with high oxidation states or reactive oxygen species, such as the oxygen centered radical, is of great scientific interest, as they have key applications as oxidizing agents, catalysts, or reaction intermediates. Due to the high reactivity of such chemical entities, experimental investigations of their electronic structures are limited. The study of small systems as models can be used to understand their properties and expand the applicability of related materials. This work aims to investigate highly oxidized transition metals, bringing a new perspective towards their electronic structure and properties. For that, X ray absorption spectroscopy, at the oxygen K and metal M3 or N3 edges of [MOn] molecular ions M transition metal, n integer , is used to identify the spectroscopic signatures of oxygen ligands and assign the oxidation state of the metal. The highly oxidized [MOn] gas phase species are produced by argon sputtering of a metal target in the presence of oxygen. The X ray absorption spectroscopy, performed in ion yield mode, is used here as a tool to directly probe the electronic ground state structure of the investigated samples, that are analysed in stable conditions in their lowest energy states. The highest oxidation state of rhodium is here presented for the first time in the trioxidorhodium VII cation, for which the rhodium M3 edge shows the chemical shift corresponding to its high oxidation state, while the oxygen K edge shows the spectral signature of oxo ligands. Further, the oxygen centered radical tetroxidoruthenium VIII cation and diradical tetroxidorhenium VII cation are here investigated by X ray absorption spectroscopy for the first time, where the oxygen centered singly occupied molecular orbitals are identified by a low energy transition at the oxygen K edge, which is suppressed upon hydrogenation. Computational studies corroborate the experimental observations, that will hopefully contribute to the scientific knowledge of these species and their oxidative propertie

Magnetic properties of the spiral spin liquid and surrounding phases in the square lattice XY model

Spiral spin liquids possess a subextensively degenerate ground state manifold, represented by a continuum of energy minima in reciprocal space. Since a small change of the spiral state wave vector requires a global change of the spin configuration in real space, it is a priori unclear how such systems can fluctuate within the degenerate ground state manifold. Only recently it was proposed that momentum vortices are responsible for the liquidity of the spiral phase and that these systems are closely related to an emergent rank 2 U 1 gauge theory H. Yan et al. [Phys. Rev. Res. 4, 023175 2022 ]. As a consequence of this gauge structure, fourfold pinch point singularities were found in a generalized spin correlator. In this paper, we use classical Monte Carlo and molecular dynamics calculations to embed the previously studied spiral spin liquid into a broader phase diagram of the square lattice XY model. We find a multitude of unusual phases and phase transitions surrounding the spiral spin liquid such as an effective four state Potts transition into a collinear double striped phase resulting from the spontaneous breaking of two coupled amp; 8484;2 symmetries. Since this phase is stabilized by entropic effects selecting the momenta away from the spiral manifold, it undergoes a second phase transition at low temperatures into a nematic spiral phase which only breaks one amp; 8484;2 symmetry. We also observe a region of parameters where the phase transition into the spiral spin liquid does not break any symmetries and where the critical exponents do not match those of standard universality classes. We study the importance of momentum vortices in driving this phase transition and discuss the possibility of a Kosterlitz Thouless transition of momentum vortices. Finally, we explore the regime where the rank 2 U 1 gauge theory is valid by investigating the fourfold pinch point singularities across the phase diagra

Sb2S3 solar cells with TiO2 electron transporting layers synthesized by ALD and USP methods

Electronic characteristics were investigated for solar cells SCs based on FTO TiO2 Sb2S3 P3HT Au structure, employing TiO2 electron transport layers ETLs fabricated by two different methods ultrasonic spray pyrolysis USP and atomic layer deposition ALD . Regardless of the deposition method, both ALD and USP TiO2 exhibit the anatase crystal structure. The calculated crystallite sizes, derived from the 101 reflection of TiO2 layers using the Scherrer equation, show minimal variance between the two methods, with values 25 nm for USP and 30 nm for ALD TiO2, respectively. Optical band gaps Eg were found to be 3.31 eV and 3.35 eV for USP and ALD methods, respectively. Exploring the thickness series of ALD TiO2, ranging from 100 to 1000 cycles approximately 5 75 nm , solar cell performance was evaluated, with the highest power conversion efficiency PCE of 3.3 achieved using ALD TiO2 of 400 cycles approximately 30 nm thick . Notably, SCs featuring USP TiO2 ETL layers, with a thickness of approximately 35 40 nm, outperform their ALD TiO2 counterparts, improving PCE by 15 , recording 4.0 versus 3.3 , respectively. This superiority in PCE is attributed to the more favorable conduction band minimum CBM position of USP TiO2 relative to the Fermi level, as revealed in the band diagram. Specifically, a lower CBM spike at the USP TiO2 Sb2S3 interface indicates reduced recombination rates compared to those at the ALD TiO2 Sb2S3 interface. This study offers valuable insights into enhancing SC performance by optimizing deposition methods and synthesis parameters of ETL layer

Structural Modulation of Nanographenes Enabled by Defects, Size and Doping for Oxygen Reduction Reaction

Nanographenes are among the fastest growing materials used for the oxygen reduction reaction ORR thanks to their low cost, environmental friendliness, excellent electrical conductivity, and scalable synthesis. The perspective of replacing precious metal based electrocatalysts with functionalized graphene is highly desirable for reducing costs in energy conversion and storage systems. Generally, the enhanced ORR activity of the nanographenes is typically deemed to originate from the heteroatom doping effect, size effect, defects effect, and or their synergistic effect. All these factors can efficiently modify the charge distribution on the sp2 conjugated carbon framework, bringing about optimized intermediate adsorption and accelerated electron transfer steps during ORR. In this review, the fundamental chemical and physical properties of nanographenes are first discussed about ORR applications. Afterward, the role of doping, size, defects, and their combined influence in boosting nanographenes ORR performance is introduced. Finally, significant challenges and essential perspectives of nanographenes as advanced ORR electrocatalysts are highlighte

Boon and Bane of Local Solid State Chemistry on the Performance of LSM Based Solid Oxide Electrolysis Cells

High temperature solid oxide cells are highly efficient energy converters. However, their lifetime is limited by rapid deactivation. Little is known about the local, atomic scale transformation that drive this degradation. Here, reaction induced changes are unraveled at the atomic scale of a solid oxide electrolysis cell SOEC operated for 550 h by combining high resolution scanning transmission electron microscopy with first principles and force field based atomistic simulations. We focus on the structural evolution of lanthanum strontium manganite LSM yttria stabilized zirconia YSZ regions and the corresponding solid solid interface. It is found that the strong inter diffusion of cations leads to the additional formation and growth of a multitude of localized structures such as a solid solution of La Mn, nano domains of secondary structures or antisite defects in the YSZ, as well as a mixed ion and electron conduction region in the LSM and complexion. These local structures can be likewise beneficial or detrimental to the performance, by either increasing the catalytically active area or by limiting the supply of reactants. The work provides unprecedented atomistic insights into the influence of local solid state chemistry on the functioning of SOECs and deepens the understanding of the degradation mechanism in SOECs, paving the way towards nanoscopic rational interface design for more efficient and durable cell

High Temperature Growth of CeOx on Au 111 and Behavior under Reducing and Oxidizing Condition

Inverse oxide metal model catalysts can show superior activity and selectivity compared with the traditional supported metal oxide architecture, commonly attributed to the synergistic overlayer support interaction. We have investigated the growth and redox properties of ceria nanoislands grown on Au 111 between 700 and 890 C, which yields the CeO2 Au 111 model catalyst system. We have observed a distinct correlation between deposition temperature, structural order, and oxide composition through low energy electron microscopy, low energy electron diffraction, intensity voltage curves, and X ray absorption spectroscopy. Improved structural order and thermal stability of the oxide have been achieved by increasing the oxygen chemical potential at the substrate surface using reactive oxygen O O2 instead of molecular O2 during growth. In situ characterization under reducing H2 and oxidizing atmospheres O2, CO2 indicates an irreversible loss of structural order and redox activity at high reduction temperatures, while moderate temperatures result in partial decomposition of the ceria nanoislands Ce3 Ce4 to metallic cerium Ce0 . The weak interaction between Au 111 and CeOx would facilitate its reduction to the Ce0 metallic state, especially considering the comparatively strong interaction between Ce0 and Au0. Besides, the higher reactivity of atomic oxygen promotes a stronger interaction between the gold and oxide islands during the nucleation process, explaining the improved stability. Thus, we propose that by driving the nucleation and growth of the ceria Au system in a highly oxidizing regime, novel chemical properties can be obtaine