321034 research outputs found
Sort by
3D structure of protein networks and lipid globules in heat-treated egg yolk revealed by x-ray holo-tomography
No full textUpon heating, egg yolk transforms from a liquid to a grainy gel due to a combination of lipid aggregation, protein denaturation-aggregation-gelation and other processes. This heat-induced solidification of egg yolk can serve as a useful model system for the investigation of protein denaturation and gelation in biological systems in general. Using x-ray holographic tomography, we studied the heat-induced changes in egg yolk on the micron to sub-micron length scale. In contrast to electron microscopy, x-ray holography does not require sample staining, fixation, or drying, which potentially alter the sample and harm sample fidelity. Our results reveal a developing separation between proteins and lipids with fatty components rapidly aggregating into large globules around 40 µm in size
Probing the Biological Identity of Inorganic Nanoparticles with Anomalous Small Angle X‐Ray Scattering
No full textIn a biological milieu, nanoparticles (NPs) undergo alterations that go from aggregation or degradation to the adsorption of a corona of proteins. Those changes influence significantly the intrinsic properties and biological capacities of the engineered nanomaterials and need to be fully understood for the successful biomedical use of NPs. Synchrotron anomalous small-angle X-ray scattering (ASAXS) is used to probe the individual small-angle X-ray scattering (SAXS) contributions from the different components of NPs (core, polymeric coating, and protein corona) on several in vitro systems. By applying a model-based fitting approach combined with pair distance distribution analysis, it is possible to investigate whether and to what extent proteins formed a corona around different nanoparticles. The results obtained agree with well-established dynamic light scattering and transmission electron microscopy experiments, confirming the capacity of ASAXS to obtain full information from complex NP samples, and opening for its use in more realistic biological environments
Texture tomography with high angular resolution utilizing sparsity
No full textWe demonstrate a novel approach to the reconstruction of scanning probe x-ray diffraction tomography data with anisotropic poly crystalline samples. The method involves reconstructing a voxel map containing an orientation distribution function in each voxel of an extended 3D sample. This method differs from existing approaches by not relying on a peak-finding and is therefore applicable to sample systems consisting of small and highly mosaic crystalline domains that are not handled well by existing methods. Samples of interest include bio-minerals and a range of small-graines microstructures common in engineering metals. By choosing a particular kind of basis functions, we can effectively utilize non-negativity in orientation-space for samples with sparse texture. This enables us to achieve stable solutions at high angular resolutions where the problem would otherwise be under determined. We demonstrate the new approach using data from a shot peened martensite sample where we are able to map the twinning micro structure in the interior of a bulk sample without resolving the individual lattice domains. We also demonstrate the approach on a piece of gastropods shell with a mosaic micro structure
Hard X-ray stereo ptychography with multi-slicing
No full textOur newly developed technique of stereoscopic ptychography allows us to scan the sample simultaneously with two nanofocused x-ray beams at different angles. The stereoscopic views can, similar to human vision, considerably improve the in-depth perception beyond current limits of pure 2D imaging systems using single optics. We achieved a sub-30nm lateral resolution and are able to recover phase images of two sample layers, which are separated by less than 500nm, based on stereo projections. With stereo ptychography we improved the depth resolution by one order of magnitude compared to the established multi-slice ptychography. Here, we take these capabilities a step further by applying them to thicker samples. This is done by combining layer recovery through stereo imaging with multislice ptychography
Synthesis and Characterization of Single‐Phase ReN Thin Films
No full textHerein, a systematic study is reported on the synthesis and characterization of single-phase rhenium nitride (ReN) thin films grown using a reactive dc magnetron sputtering (R-dcMS). ReN thin films are expected to be superhard (bulk modulus ≈ 400 GPa) and superconducting (Tc ≈ 5 K). Since the formation enthalpy of ReN ≈ –0.14 eV is comparatively high, a stringent control of growth parameters such as partial N2 gas flow () and growth temperature (Ts) is necessary to achieve an impurity free and single-phase ReN. The and the Ts are systematically varied during the R-dcMS process to find the optimal conditions for growth of ReN phase. Resulting samples are studied using X-ray reflectivity to determine the deposition rate, density, and roughness. The crystal structure and depth profile of ReN thin films have been probed using X-ray diffraction and secondary ion mass spectroscopy. The electronic structure is studied using hard X-ray photoelectron spectroscopy and N K-edge X-ray absorption near edge structure. The superconducting transition temperature (Tc) is found to be 3.3 K from the zero field electrical resistivity measurement. The present work constructs a phase diagram to identify the optimal conditions for forming single-phase ReN films
Heat treatment effect on microstructural evolution of cold spray additive manufacturing Ti6Al4V
No full textCold spray additive manufacturing (CSAM) has great industrial potential due toits high deposition rate and the possibility of building metallic alloys and compositeparts once the process is conducted in a solid state, preserving many rawmaterials properties. A material highly studied for CSAM is the Ti6Al4V alloy,which is used in medical implants and aeronautical structural components. Ithas a matrix of two phases with different crystallography arrangements,compact hexagonal, and body-centered cubic, which can tailor the mechanicalproperties according to its volumetric percentage. To improve CSAM-ed materialductility and strength and homogenize its residual stress, heat treatments (HTs)have been employed. These HTs sinter the deposited particles, enhancing theircohesion and other properties. This study focuses on the effect of the HT parameterson the characteristics of CSAM-ed Ti6Al4V freeform parts. HT reduces thehardness from 385 in as-sprayed condition to around 320 HV,conserving theporosity close to 4.0%, and increasing the HT temperature from 600 to 1000 °Cimproved the amount of phase β in the α grains boundaries. The findings of thisstudy will provide valuable insights into the impact of HT on the mechanicalproperties and microstructure of CSAM-ed components, thereby aiding in theoptimization of this manufacturing process for the Ti6Al4V alloy
Resistively detected electron spin resonance and g- factor in few-layer exfoliated MoS devices
No full textMoS has recently emerged as a promising material for enabling quantum devices and spintronic applications. In this context, an improved physical understanding of the g-factor of MoS depending on device geometry is of great importance. Resistively detected electron spin resonance (RD-ESR) could be employed to determine the g-factor in micron-scale devices. However, its application and RD-ESR studies have been limited by Schottky or high-resistance contacts to MoS. Here, we exploit naturally n-doped few-layer MoS devices with ohmic tin (Sn) contacts that allow the electrical study of spin phenomena. Resonant excitation of electron spins and resistive detection is a possible path to exploit the spin effects in MoS devices. Using RD-ESR, we determine the g-factor of few-layer MoS to be ∼1.92 and observe that the g-factor value is independent of the charge carrier density within the limits of our measurements
Temperature-dependent deformation behavior of the additively manufactured AlCrFeNi alloy using in-situ high energy X-ray diffraction
No full textLaser powder bed fusion of the hypo-eutectic eutectic alloy AlCrFeNi conveniently produces an ultrafine quasi-lamellar microstructure composed of fcc and bcc phases. This is achieved by annealing the as-built and almost fully fcc microstructure, which has been published previously. In this study, two different annealing treatments were carried out, i.e. at 900 °C and 1000 °C for 6 h. The samples were compressed at temperatures up to 800 °C using in-situ high energy synchrotron X-ray diffraction (HEXRD). This technique provides studying macroscopic and phase-specific stress-strain evolution and therefore more insight into the stress partitioning as a function of test temperature between fcc A1 and bcc ordered B2. This analysis shows that below 400°C B2 is the major contributor to hardening, while above 600°C A1 contributes more, suggesting the softening of B2. The ultra-fine quasi-lamellar structure with confined B2 lamellae induces remarkably high dislocation density and hardening, as well as co-deformation of both phases. The dislocation density evolution was used to describe the macroscopic flow stress-strain using a phase fraction-weighted Taylor equation. The temperature capability of the novel material was compared with established materials and bridges the gap between steels and Ni-based alloys for applications up to 650 °C
Virtual Special Issue on Attosecond Chemistry
No full textAttosecond science, established at the dawn of this millennium and recently recognized by the 2023 Nobel Prize in Physics awarded to Pierre Agostini, Ferenc Krausz, and Anne L’Huillier, has given access to the natural time scale of electronic motion in matter. For this reason, since its early days, scientists have sought potential applications in other fields of science where electron dynamics play an important role. One of them is chemistry, because the way molecules behave, e.g., forming or breaking bonds, is ultimately dictated by electronic motion, which paves the way for nuclear motion. Since the first observation in 2010 of attosecond electron dynamics in molecular hydrogen, more and more complex systems have been under scrutiny, leading to the birth of the new discipline of Attosecond Chemistry or Attochemistry. High-harmonic generation (HHG) sources and X-ray free electron lasers (XFELs) can now routinely generate light pulses of sub-femtosecond duration, thus providing access to the attosecond time scale. This has required the joint effort of physicists and chemists─both experimentalists and theoreticians─in order to develop ever-improved methods for both visualization and control of electron dynamics. Physical chemistry, and chemistry in general, can greatly benefit from these developments, because new, unforeseen possibilities to control chemical reactions may arise in the future. These are the goals of the AttoChem (https://attochem.qui.uam.es/) and X-Lites (https://opticalscience.osu.edu/x-lites) international networks, which gather the most prominent research groups working in Attosecond Chemistry.The present Virtual Special Issue provides a collection of original scientific papers that address problems of special relevance in attochemistry, in particular, the electron and charge dynamics triggered by extreme ultraviolet (XUV) attosecond pulses, strong IR fields, or attosecond or few-femtosecond X-ray pulses generated in XFELs; the electron dynamics associated with the ionization process itself; and the ultrafast nuclear dynamics that coexist or follow the electron dynamics induced by the above sources
Size-dependent stress response of nanoscale B2 intermetallic precipitates revealed by in-situ high-energy X-ray diffraction
No full textIn-situ high-energy X-ray diffraction experiments under uniaxial loading revealed the stress distribution among austenite, ferrite, and nanoscale B2-(Ni,Fe)Al intermetallic precipitates embedded in the ferrite phase of an Al-added lightweight steel. Stress analysis based on the lattice strains induced by uniaxial tensile loading, while assuming a uniaxial stress state within the grains and neglecting residual stresses, indicated earlier yielding of austenite and the development of higher stresses in ferrite. Remarkably, at an applied true stress of nearly 1.0 GPa, stresses up to about 5.8 GPa were determined within the B2 precipitates. The stress level within the B2 precipitates, which exhibited a bimodal size distribution, was strongly size-dependent, with the finer population experiencing higher stresses. Due to the low Schmid factor for {hkl}〈100〉 slip as the preferred slip system in B2, plastic deformation of B2 in this hard orientation was enabled by 〈111〉 slip, aided by the penetration of 1/2 〈111〉 dislocations gliding on {110} planes in the cube-on-cube-related ferrite. The high stresses in B2 upon loading along the 〈100〉 direction raised the stress level in the surrounding ferrite, which is a likely cause of {100} cleavage in embrittled body-centered cubic steels. This study enhances our understanding of the micromechanical behavior of precipitation-strengthened alloys and elucidates how matrix-precipitate interactions influence macroscopic mechanical properties