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Examination of spectroscopic and thermographic qualities of Tm-doped and Yb/Er co-doped germanate tellurite glasses
No full textOxyfluride Germanate Tellurite glasses single doped with (Tm3+) thulium, (Tm3+,Yb3+) thulium / ytterbium co-doped and (Tm3+,Yb3+,Er3+) thulium / ytterbium / erbium triple-doped were fabricated. Room temperature absorption spectra were employed to evaluate the relevant radiative transition rates and branching ratio of luminescence. Distribution of the measured emission lines within UV–vis spectral region is considerably different when the selective excitation wavelengths at 358 nm and 445 nm were utilized. The excellent color purity exceeding 90 % was estimated for Tm-doped glass luminescence. The significant quantum efficiency of thulium first excited state and the related NIR emission cross section indicate potential optical amplification between 1908–2080 nm. Effective broad band tellurium optical spectra were examined employing synchrotron radiation. Ultrashort laser pulse excitations disclosed the different relaxation dynamic of the excited states and the involved interionic phenomena. Luminescence intensity ratios as function of temperature were determined for some diverse combinations of the measured bands originating in thermally coupled and non-thermally coupled levels. The highest value of relative sensitivity Sr=0.78 %K-1 at T = 350 K was acquired for a Tm/Yb/Er co-doped glass utilizing both anti-Stokes emissions of thulium and erbium
Mechanistic insights into methanol production on NiGa thin films: An in situ XPS and DFT study
No full textThe intermetallic compound δ-Ni5Ga3 has emerged as a promising catalyst for CO2 hydrogenation to methanol, offering high selectivity at low-pressure operation, and enhanced stability compared to conventional Cu/ZnO catalysts. However, the fundamental understanding of its active sites, reaction mechanisms, and deactivation pathways remains incomplete, hindering its further development. In this study, we utilize well-defined δ-Ni5Ga3 thin film model catalysts synthesized via magnetron sputtering to investigate these aspects under realistic reaction conditions. We investigate the evolution of the catalyst with temperature employing in situ ambient pressure X-ray photoelectron spectroscopy (AP-XPS) at 300 mbar, microreactor activity measurements, temperature-programmed desorption (TPD), and density functional theory (DFT) calculations. Our experiments show the active catalyst as mostly metallic with only small amounts on oxidized gallium, which gradually reduces and gives way to an increased nickel-concentration at the surface at higher temperatures, accompanied by carbide-growth. We further observe the temperature-evolution of key intermediates, such as carboxyl, formate, and methoxy species. Based on these observations, we discuss distinct pathways for methanol synthesis and CO2 methanation, with methoxy formation correlating directly with methanol activity, as well as the deactivation mechanism
Effect of solution and aging on the texture evolution of an extruded metastable β titanium alloy Ti-4Al-6V-5Mo-3Cr-1Zr
No full textCompared to α + β titanium alloys, β titanium alloys exhibit superior heattreatment strengthening effects. Specifically, after solid solution treatmentfollowed by two-stage aging, the alloy features finer secondary α (αs) phasescompared to primary α (αp) phases, resulting in enhanced second phasestrengthening effects. This study focuses on the effects of various agingparameters on the texture evolution of an as extruded high strength metastableβ titanium alloy Ti-4Al-6V-5Mo-3Cr-1Zr using synchrotron high-energy X-raydiffraction and electron microscopy. After extrusion, two primary fiber texturesare formed within the β phase: and fiber texture. The intensityof β phase texture fluctuates during aging primarily attributed to phasetransformations altering the volume fractions of the two phases. The α phasepredominantly exhibited the conventional fiber texture, along with anunconventional component rarely reported in prior studies of metastableβ titanium alloys, with their orientations rotating during high-temperature aging.This rotation originates from variant selection during the precipitation of αsphase from the β matrix, leading to crystallographic orientations distinct fromthe preferred orientation of αp phase formed during extrusion
Harnessing interfacial entropic effects in polymer grafted nanoparticle composites for tailoring their thermo-mechanical and separation properties
No full textNanocomposites based on polymeric materials have been extensively studied to understand and control the thermodynamics, flow, and mechanical properties of the underlying matrix as well to create new materials with diverse optical, electrical, magnetic, separation, catalytic, and biomedical properties. In the form of thin films or membranes, such materials can impart remarkable improvements in various properties of the underlying substrates. Using nanoparticles with grafted polymer chains usually overcomes a major hurdle in achieving enhancements in various properties by enabling better dispersion in the matrix while at the same time introducing a new parameter – interfacial entropy – leading to the emergence of new parameter space for tuning dispersion, flow and thermal properties. In this article, we highlight how this interfacial entropic effect can be harnessed to control various properties in thin films and membranes of grafted nanoparticle composites, in particular their thermo-mechanical properties, viscosity, fragility, glass transition temperature (Tg), and dynamic heterogeneity as well as their ability to act as highly selective gas separation and water desalination membranes. We discuss the application of a range of experimental techniques as well as molecular dynamics simulation to extract these properties and obtain microscopic insight into how the interplay of various surface and interfacial effects lies at the centre of these significant property improvements and enhanced functionality. Finally, we provide an outlook on future opportunities for designing sustainable PNCs, emphasizing their potential in environmental, energy, and biomedical applications, with advanced experiments and modelling driving further innovations
Synchrotron Micro‐X‐Ray Fluorescence Elemental Imaging Reveals Zinc Distribution in the Hyperaccumulator Sedum plumbizincicola (Crassulaceae)
No full textSedum plumbizincicola is a zinc–cadmium (Zn–Cd) hyperaccumulator native to China with high potential for use in the phytoremediation of contaminated soils in temperate climates. This study aimed to determine the Zn accumulation and distribution in S. plumbizincicola tissues grown on soils co-contaminated with Cd, Pb, and Zn. The efficiency of Zn accumulation was assessed in monoculture and intercropping systems with Noccaea caerulescens. The samples were analyzed by inductively coupled plasma–atomic emission spectrometry and synchrotron micro-X-ray fluorescence elemental imaging. Sedum plumbizincicola grown in monoculture had significantly higher foliar Zn concentrations than the plants grown with N. caerulescens, with the leaf tips, petioles and nodes being the main sites of Zn localization in the aerial parts. The highest Zn concentrations were observed in the epidermis and vascular system of both leaves and stems, with the distribution pattern differing between young and mature leaves. This study highlights the Zn localization patterns in S. plumbizincicola to improve our understanding of the underlying mechanisms of Zn hyperaccumulation. Growing in monoculture, S. plumbizincicola is an effective candidate for Zn agromining or phytoremediation of Zn-Cd contaminated soils, with less promising results when intercropped with N. caerulescens
Defect Engineering in Ti‐Doped TaN Thin Films for Enhanced Photoelectrochemical Water Splitting: Electronic Structure Modulation and Charge Carrier Dynamics
No full textTantalum nitride (TaN) is a promising semiconductor for solar-driven photoelectrochemical (PEC) water splitting, but its performance is limited by intrinsic defects. Here, we investigate the effect of titanium (Ti) doping (0–10 at%) on the structural, compositional, and optoelectronic properties of TaN thin films. At low concentrations (<2 at%), Ti preferentially substitutes Ta at four-coordinated sites, enhancing nitrogen incorporation and suppressing defect states associated with under-coordinated Ta. This leads to improved carrier dynamics and prolonged electron–hole lifetimes. Higher doping levels (≥3.5 at%) result in occupation of three-coordinated sites, inducing increase in the oxygen content, lattice distortion, and defect formation that deteriorate carrier lifetimes. PEC measurements reveal that optimized Ti doping significantly reduces charge transfer resistance and nearly seven-fold increase in the photocurrent. These findings underscore the importance of controlled Ti doping for defect engineering and band structure tuning to boost the PEC performance of TaN thin films
Mathematical and Computational Analysis of Vacuum Structures in Extended Higgs Sectors
No full textAmong other restrictions, vacuum stability is a theoretical constraint for vacuumconfigurations in BSM theories to be allowed or excluded. But due to multidimensionalfield spaces, computing the vacuum stability is a challenging task. This thesis investi-gates vacuum structures in the N2HDM and the cS2HDM and examines the possibilityto take multiple vacuum decay channels into account. It also introduces three differentalgorithms to compute vacuum stability and compares them. One of these algorithmsis the recently developed code NNBounce that has been refined with a hyperparameteroptimization algorithm and is made publicly available
Tuning the structural, electronic, and magnetic properties of CoFeO thin films via swift heavy ion irradiation
No full textThe present work explores the effect of 120 MeV Au9+ ion irradiation on the structural, electronic, and magnetic behavior of CoFe2O4 (CFO) thin films, prepared by Pulsed Laser deposition (PLD) technique. Grazing incidence X-ray diffraction (GIXRD) analysis revealed that with increasing ion fluences there is peak broadening and decrease in diffraction intensity, which results reduction in crystallite size and partial amorphization. X-ray photoelectron spectroscopy (XPS) analysis showed an increase in oxygen vacancy concentration, accompanied by partial reduction of Co and Fe cations. A decrease in saturation magnetization and enhanced coercivity has been observed with increasing ion fluence, consistent with defect-induced pinning. Law of Approach to Saturation (LAS) fitting on the hysteresis curve has been carried out for the estimation of the effective anisotropy constant (Keff), which provides the quantitative evidence of irradiation-induced magnetic anisotropy enhancement. X-ray magnetic circular dichroism (XMCD) confirmed element-specific changes in magnetic moments. The observed results are explained in terms of disruption in superexchange interactions of Co2+−O2−−Fe3+ after ion irradiation due to significant modifications in the oxidation states of Co and Fe ions within CFO thin films
CP-violation in production of heavy neutrinos from bubble collisions
No full textFirst order phase transitions (FOPT) in the early Universe can be powerful emitters of both relativistic and heavy particles, upon the collision of ultra-relativistic bubble shells. If the particles coupling to the bubble wall have CP-violating interactions, the same collision process can also create a local lepton or baryon charge. This CP-violation can originate from different channels, which have only been partially addressed in the literature. We present a systematic analysis of the different channels inducing CP-violation during bubble collisions: 1) the decay of heavy particles 2) the production of heavy particles and 3) the production of light and relativistic Standard Model (SM) particles.As an illustration of the impact that such mechanisms can have on baryon number and dark matter (DM) abundance, we then introduce a simple model of cogenesis, separating a positive and a negative lepton number in the SM and a dark sector. The lepton number asymmetry in the SM can be used to explain the baryon asymmetry of the Universe (BAU), while the opposite asymmetry in the dark sector is responsible for determining the abundance of DM. Moreover, the masses of light neutrinos can be understood via the inverse seesaw mechanism, with the lepton-violating Majorana mass originating from the FOPT.A typical signal produced by a FOPT is the irreducible gravitational wave (GW) background. We find that a substantial portion of the parameter space can be probed at future observatories like the Einstein Telescope (ET)
In-situ synchrotron high energy X-ray diffraction study on the internal strain evolution of an extruded Ti-45Al-8Nb-0.2C alloy during high-temperature compression
No full textDue to their exceptional properties, γ-TiAl based alloys present substantial prospect for aerospace and automotiveapplications. However, the significant disparity in plasticity between the D019-α2 and L10-γ phases greatlyaffects TiAl alloys’ service behavior. This study investigates the internal strain accumulation in the α2 and γphases of an extruded Ti-45Al-8Nb-0.2C alloy during compression at 900 ◦C and the subsequent stress relaxationbehavior during annealing at 850 ◦C, using in situ synchrotron high-energy X-ray diffraction (HEXRD). Duringcompression, the γ phase starts to yield plastically at approximately 410 MPa true stress, progressively shiftingthe load to the α2 phase and generating high residual stress in the α2 phase after deformation. However,annealing at 850 ◦C for 30 min only partially relieves the residual stress in the α2 phase, with the relaxation ratedecreasing substantially after the first 10 min. Furthermore, when the true stress reaches 790 MPa duringcompression, the α2 phase undergoes rigid-body rotation to accommodate the plastic deformation of the adjacentγ phase, initiating texture evolution that ultimately forms a distinct fiber texture