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Local-stress-mediated deformation and fracture in Ti-Al layered metals: A synchrotron and CPFEM study
No full textLayered metals (LMs), as a prototypical heterostructured material, have garnered considerable attention due to their ability to achieve excellent strength-ductility synergy. Due to the distinct mechanical properties of the component layers, the local stress in each layer often deviates from the macroscopic applied stress. In this study, synchrotron-based X-ray microdiffraction with micrometer resolution in one beam dimension was conducted. The local stress evolution in Ti-Al LM upon uniaxial applied stress was tracked via synchrotron high-energy X-ray microdiffraction (μHEXRD). Meanwhile, deformation and fracture were characterized in detail by SEM, EBSD, and synchrotron Laue X-ray microdiffraction (μLXRD). Such detailed experimental studies revealed the local stress evolution in Ti-Al LM follows four stages, and the deformation and fracture of the layers differed from those of free-standing counterparts. The effects of local stress on deformation and fracture were discussed with the aid of the crystal plasticity finite element method (CPFEM), elucidating the slip system activation from the view of resolved shear stress and the intergranular fracture from the view of stress triaxiality. This work contributes to the fundamental understanding of the mechanical behaviors of LMs and offers guidance for designing high-performance LMs
Search for dark matter produced in association with a Higgs boson decaying to bottom quarks in proton-proton collisions at = 13 TeV
No full textA search for dark matter particles produced in association with a Higgs boson decaying to a bottom quark-antiquark pair in proton-proton collisions at = 13 TeV is presented. The data, collected with the CMS detector at the LHC, correspond to an integrated luminosity of 101 fb. The analysis is performed in exclusive categories targeting both Lorentz-boosted (merged) and resolved b jet pair topologies, covering a wide range of Higgs boson transverse momentum. A statistical combination is made with a previous search using data collected in 2016 and corresponding to an integrated luminosity of 35.9 fb. The observed data agree with the standard model background predictions. Constraints are placed on models predicting new particles or interactions, such as those in the simplified frameworks of baryonic-Z' and 2HDM+a, where the latter is a type-II two-Higgs-doublet model featuring a heavy pseudoscalar with an additional light pseudoscalar. Upper limits at 95% confidence level are set on the production cross section for these models. For the baryonic-Z' model, Z' boson masses below 2.25 TeV are excluded for a dark matter particle candidate mass of 1 GeV. In the 2HDM+a model, heavy pseudoscalar masses between 850 and 1300 GeV are excluded for a light pseudoscalar mass of 350 GeV
Simultaneous probe of the charm and bottom quark Yukawa couplings using events
No full textA search for the standard model Higgs boson decaying to a charm quark-antiquark pair, H , produced in association with a top quark-antiquark pair (H) is presented. The search is performed with data from proton-proton collisions at = 13 TeV, corresponding to an integrated luminosity of 138 fb. Advanced machine learning techniques are employed for jet flavor identification and event classification. The Higgs boson decay to a bottom quark-antiquark pair is measured simultaneously and the observed H bb event rate relative to the standard model expectation is 0.91. The observed (expected) upper limit on the product of production cross section and branching fraction (H)(H ) is 0.11 (0.13) pb at 95% confidence level, corresponding to 7.8 (8.7) times the standard model prediction. When combined with the previous search for H via associated production with a W or Z boson, the observed (expected) 95% confidence interval on the Higgs-charm Yukawa coupling modifier, , is 3.5 (2.7), the most stringent constraint to date
Engineered Self‐Assembly of Plasmonic Gold Nanoparticles Into Two‐Dimensional and Three‐Dimensional Arrays Within the Pores of Porous Silicon Membranes
No full textWe report a facile centrifugation-based method for assembling polystyrene (PSSH)-functionalized gold nanoparticles (Au NPs)onto porous silicon (pSi) substrates in two distinct configurations: two- and three-dimensional (2D and 3D) assemblies. The 2Dassemblies are densely packed monolayer coatings of the exposed Si-surfaces including the inner pore walls, whereas the 3Dstructures result from Au NPs clustering inside the pores. Remarkably, this shift from 2D to 3D architectures was achievedby minor modification of the PSSH coating thickness. Scanning electron microscopy (SEM) characterization confirmed the homo-geneity and high packing density of these assemblies extending over several thousand square micrometers. This approach offers astraightforward and versatile route for the fabrication of well-ordered pSi–Au NP hybrid nanostructures with potential applica-tions in catalysis, surface-enhanced spectroscopy and optical metamaterials
Evolution of precipitation in a duplex Fe-Mn-Al-C low-density steel revealed by in situ high-energy synchrotron X-ray diffraction
No full textAdvanced duplex low-density (LD) steels with an austenite-based matrix are promising candidates for transportation applications. In these steels, the austenite remains the stable matrix phase; however, when subjected to heat treatment, it becomes thermodynamically unstable, promoting phase transformations. These transformations lead to the formation of κ-carbides and ferrite, which significantly affect the mechanical behavior of the LD steel. Thus, understanding their precipitation kinetics is paramount for the design of thermo-mechanical treatments. This study focuses on investigating the phase evolution in a Fe-12Mn-8Al-1C duplex LD steel during aging treatment using in situ high-energy synchrotron X-ray diffraction combined with dilatometry. The results obtained revealed the onsets of transformation, confirming the evolution of κ and ferrite phases. The phase volume fractions were determined by Rietveld refinement of the diffraction data. Additionally, microstructural characterization using light optical microscopy (LOM), scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) verified the austenite as a matrix phase and the presence of second-phases, including ferrite and κ’- and κ*-carbides, after aging. These findings provide a comprehensive understanding of phase evolution, enabling the optimization of processing routes for LD steels
Atomic level mechanism of nanoripple formation on silicon by oblique angle irradiation with molecular nitrogen ions
No full textReactive ion beam sputtering is an efficient tool to produce modifications in the surface topography in the form of periodic nanoripples with controlled modulation period and amplitude. In the present work, the atomic level processes responsible for nanoripple formation on silicon surface by oblique angle irradiation with molecular nitrogen ions have been studied. A variety of complementary techniques have been used to elucidate the structural and compositional changes occurring in the surface and sub-surface regions with irradiation fluence. It is shown that the implanted nitrogen ions react with the Si substrate to form SiN phase in the subsurface region. GI-SAXS measurements suggest that the buried nitride layer gets phase separated to generate periodic variation in the density at nanometer length scale. With increasing fluence, the surface layer of Si gets sputtered out and the nitride layer reaches the surface. At this stage an unequal sputtering of nitride-rich and nitride-depleted regions results in development of surface instability which is already periodic in nature. Further irradiation results in development of well-defined surface ripples as a combined effect of composition-dependent and curvature-dependent sputtering. A direct chemical evidence for the phase separation of the nitride layer comes from the Auger electron scanning microscopy
Laser-induced alignment of nanoparticles and macromolecules for single-particle-imaging applications
No full textLaser-induced alignment of particles and molecules was long envisioned to support three-dimensional structure determination using “single-molecule diffraction” with X-ray free-electron lasers [PRL 92, 198102 (2004)]. However, the alignment of isolated macromolecules has not yet been demonstrated also because quantitative modeling is very expensive. We computationally demonstrated that the alignment of nanorods and proteins is possible with a standard laser technology. We performed a comprehensive analysis on the dependence of the degree of alignment on molecular properties and experimental details, e.g., particle temperature and laser-pulse energy. Considering the polarizability anisotropy of about 150,000 proteins, our analysis revealed that most of these proteins can be aligned using realistic experimental parameters
Bright electron bunches from a plasma-wakefield accelerator with a steep density down-ramp
No full textHigh-brightness electron bunches drive fundamental research in particlephysics and photon science. Key to achieving a high brightness is to have a lowtransverse emittance, which ensures that the bunch can be tightly focussed. Inradiofrequency accelerators a low initial emittance can be rapidly degradeddue to space charge forces, which are greatly diminished once the electronbunch attains a relativistic velocity. A plasma accelerator can maintain orders-of-magnitude higher accelerating fields than radiofrequency accelerators,while multiple techniques exist to create a low emittance electron bunchdirectly inside the plasma accelerator structure. Plasma accelerators thereforeoffer a possibility to create high-brightness bunches in wakefields driven evenby low-quality drive bunches. Here we demonstrate the injection and gigavolt-per-metre acceleration of electron bunches with mm-mrad normalised emit-tance, O(10 pC/MeV) spectral density and per-cent-level energy spread, all withexcellent reproducibility
SSZ‐13 Zeolite with Isolated Co<sup>2+</sup> Sites as an Efficient and Durable Catalyst System for Non‐Oxidative Ethane Dehydrogenation
No full textNon-oxidative dehydrogenation of ethane (EDH) is an attractive method for on-purpose ethene production, but achieving high activity and, especially, durability with catalysts based on earth-abundant metals remains challenging. Herein, we introduce the Co/SSZ-13 system with exclusively divalent cobalt (Co2+) ions that meets the above requirements. The use of complementary characterization techniques enabled us to reveal two Co2+ species: Co2+─Z2 located in the six-membered-ring windows and [Co(OH)]+─Z in the eight-membered-ring windows, with Z representing a charged zeolite framework site. A quantitative correlation between the rate of ethene formation and the site population establishes Co2+─Z2 as the active species. In situ X-ray absorption spectroscopy confirms their structural and electronic stability under high-temperature reaction conditions. The optimized 0.9Co/SSZ-13 (0.9Co) catalyst showed highly durable operation over 200 dehydrogenation/oxidative regeneration cycles at 600–650°C lasting for 150 h with industrially relevant productivity. In this regard, it outperforms almost all previously developed catalysts even those with platinum as an active component. The obtained results uncover the atomic-level origins of EDH activity/durability of the Co/SSZ-13 system and highlight the critical role of metal site location in designing highly active, selective, and durable catalysts for on-purpose ethene production
Role of Cu doping in promoting diffusion-assisted evolution of magnetic properties in equiatomic FeNi films
No full textThe increasing need for environment-friendly substitutes for rare-earth-based magnets has sparked interest in materials such as the L10-ordered FeNi (tetrataenite) phase, which possesses high magnetocrystalline anisotropy and saturation magnetization. Despite being a promising candidate, preparation of this ordered phase in the laboratory remains a challenge due to the slow diffusion kinetics that prevent atomic ordering under normal conditions. From the theoretical estimations and experimental results, Cu is known for accelerating the atomic interdiffusion and promoting chemical disorder, which may facilitate the grain boundary diffusion. In the present work, chemically homogeneous multilayers of equiatomic FeNi and Cu-doped FeNi (5 at.%) were studied to investigate the correlation between self-diffusion and magnetism. Nuclear resonance reflectivity and forward scattering measurements on as-deposited and annealed samples showed that Cu doping substantially increases self-diffusion, which is in agreement with significant changes in the local magnetic environment, as supported by conversion electron Mossbauer ¨ spectroscopy. Although the net magnetic moment remained nearly unchanged, an enhancement in the coercivity at 573 K was observed in the Cu-doped sample, as quantified by SQUID-VSM. These observations highlight the potential of Cu-assisted diffusion channels to facilitate the formation of ordered phases in FeNi systems as a strategic approach to the development of rare-earth-free permanent magnets