| 1. |
- Farmand, Maryam, et al.
(author)
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Near-edge X-ray refraction fine structure microscopy
- 2017
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In: Applied Physics Letters. - : AMER INST PHYSICS. - 0003-6951 .- 1077-3118. ; 110:6
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Journal article (peer-reviewed)abstract
- We demonstrate a method for obtaining increased spatial resolution and specificity in nanoscale chemical composition maps through the use of full refractive reference spectra in soft x-ray spectro- microscopy. Using soft x-ray ptychography, we measure both the absorption and refraction of x-rays through pristine reference materials as a function of photon energy and use these reference spectra as the basis for decomposing spatially resolved spectra from a heterogeneous sample, thereby quantifying the composition at high resolution. While conventional instruments are limited to absorption contrast, our novel refraction based method takes advantage of the strongly energy dependent scattering cross-section and can see nearly five-fold improved spatial resolution on resonance.
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| 2. |
- Huang, Ningdong, et al.
(author)
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Microscopic Probing of the Size Dependence in Hydrophobic Solvation
- 2012
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In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 136:7, s. 074507-
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Journal article (peer-reviewed)abstract
- A dependence on solute size of the hydrophobic effect has been proposed based on theory and simulations, such that small apolar solutes leave the hydrogen (H-) bonding network in water intact or even strengthened, whereas hydration of larger, nanometer-sized apolar solutes breaks hydrogen bonds and creates a liquid-vapor-like interface around the solutes. Here we report the direct experimental microscopic observation of the small-to-large crossover behavior of hydrophobic effects in aqueous solutions of amphiphilic tetraalkyl-ammonium (CnH2n+1)4N + (TAA) cations with increased side chain length by probing the H-bonding network in water through O K-edge x-ray absorption spectroscopy and the solute-solute interaction using small angle x-ray scattering. These results open for unique experimental opportunities to investigate hydrophobic effects for a range of important processes in chemistry and biology.We report small angle x-ray scattering data demonstrating the direct experimental microscopic observation of the small-to-large crossover behavior of hydrophobic effects in hydrophobic solvation. By increasing the side chain length of amphiphilic tetraalkyl-ammonium (CnH2n+1)4N+ (R4N+) cations in aqueous solution we observe diffraction peaks indicating association between cations at a solute size between 4.4 and 5 Å, which show temperature dependence dominated by hydrophobic attraction. Using O K-edge x-ray absorption we show that small solutes affect hydrogen bonding in water similar to a temperature decrease, while large solutes affect water similar to a temperature increase. Molecular dynamics simulations support, and provide further insight into, the origin of the experimental observations.
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| 3. |
- Sellberg, Jonas A., et al.
(author)
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Comparison of x-ray absorption spectra between water and ice : New ice data with low pre-edge absorption cross-section
- 2014
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In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 141:3, s. 034507-
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Journal article (peer-reviewed)abstract
- The effect of crystal growth conditions on the O K-edge x-ray absorption spectra of ice is investigated through detailed analysis of the spectral features. The amount of ice defects is found to be minimized on hydrophobic surfaces, such as BaF2(111), with low concentration of nucleation centers. This is manifested through a reduction of the absorption cross-section at 535 eV, which is associated with distorted hydrogen bonds. Furthermore, a connection is made between the observed increase in spectral intensity between 544 and 548 eV and high-symmetry points in the electronic band structure, suggesting a more extended hydrogen-bond network as compared to ices prepared differently. The spectral differences for various ice preparations are compared to the temperature dependence of spectra of liquid water upon supercooling. A double-peak feature in the absorption cross-section between 540 and 543 eV is identified as a characteristic of the crystalline phase. The connection to the interpretation of the liquid phase O K-edge x-ray absorption spectrum is extensively discussed.
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| 4. |
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| 5. |
- Shapiro, David A., et al.
(author)
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Chemical composition mapping with nanometre resolution by soft X-ray microscopy
- 2014
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In: Nature Photonics. - : Springer Science and Business Media LLC. - 1749-4885 .- 1749-4893. ; 8:10, s. 765-769
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Journal article (peer-reviewed)abstract
- X-ray microscopy is powerful in that it can probe large volumes of material at high spatial resolution with exquisite chemical, electronic and bond orientation contrast1, 2, 3, 4, 5. The development of diffraction-based methods such as ptychography has, in principle, removed the resolution limit imposed by the characteristics of the X-ray optics6, 7, 8, 9, 10. Here, using soft X-ray ptychography, we demonstrate the highest-resolution X-ray microscopy ever achieved by imaging 5 nm structures. We quantify the performance of our microscope and apply the method to the study of delithiation in a nanoplate of LiFePO4, a material of broad interest in electrochemical energy storage11, 12. We calculate chemical component distributions using the full complex refractive index and demonstrate enhanced contrast, which elucidates a strong correlation between structural defects and chemical phase propagation. The ability to visualize the coupling of the kinetics of a phase transformation with the mechanical consequences is critical to designing materials with ultimate durability.
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| 6. |
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| 7. |
- Yu, Young-Sang, et al.
(author)
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Three-dimensional localization of nanoscale battery reactions using soft X-ray tomography
- 2018
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In: Nature Communications. - : NATURE PUBLISHING GROUP. - 2041-1723. ; 9
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Journal article (peer-reviewed)abstract
- Battery function is determined by the efficiency and reversibility of the electrochemical phase transformations at solid electrodes. The microscopic tools available to study the chemical states of matter with the required spatial resolution and chemical specificity are intrinsically limited when studying complex architectures by their reliance on two-dimensional projections of thick material. Here, we report the development of soft X-ray ptychographic tomography, which resolves chemical states in three dimensions at 11 nm spatial resolution. We study an ensemble of nano-plates of lithium iron phosphate extracted from a battery electrode at 50% state of charge. Using a set of nanoscale tomograms, we quantify the electrochemical state and resolve phase boundaries throughout the volume of individual nanoparticles. These observations reveal multiple reaction points, intra-particle heterogeneity, and size effects that highlight the importance of multi-dimensional analytical tools in providing novel insight to the design of the next generation of high-performance devices.
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