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Open Access Publications from the University of California

Scholarly Works (76 results)

  • Article
LBL Publications (2010)
Most interesting materials in nature are heterogeneous, so it is useful to have analytical techniques with spatial resolution sufficient to resolve these heterogeneities. This article presents the basics of X-ray photon-in/photon-out chemical imaging. This family of methods allows one to derive images reflecting the chemical state of a given element in a complex sample, at micron or deep sub-micron scale. X-ray chemical imaging is relatively non-destructive and element-selective, and requires minimal sample preparation. The article presents the basic concepts and some considerations of data taking and data analysis, along with some examples.
    Cover page: X-ray photon-in/photon-out methods for chemical imaging
    • Article
    • Peer Reviewed
    UCLA Previously Published Works (2023)
    The typical output of a STXM (Scanning Transmission X-ray (spectro)Microscopy) measurement is a data cube consisting of a set of images (measurements of X-ray transmission at a grid of pixels) taken at a sequence of incident energies. As with any experimental measurement, this raw data must be reduced to some standard form and interpreted. In this paper, I review the basics of how to go from raw data to information about the sample. I will discuss the fundamentals of X-ray spectromicroscopy, data reduction, descriptive and model-based analysis, and available software, with examples taken from the literature.
      Cover page: Data analysis in spectroscopic STXMCreative Commons 'BY' version 4.0 license
      • Article
      • Peer Reviewed
      Lawrence Berkeley National Laboratory (2004)

      The speciation of Mn, Fe, As and Zn in a fast-growing (0.02mm/yr), shallow-marine ferromanganese nodule has been examined by micro X-ray fluorescence, micro X-ray diffraction, and micro X-ray absorption spectroscopy. This nodule exhibits alternating Fe-rich and Mn-rich layers reflecting redox variations in water chemistry. Fe occurs as two-line ferrihydrite. The As is strictly associated with Fe and is mostly pentavalent, with an environment similar to that of As sorbed on or coprecipitated with synthetic ferrihydrite. The Mn is in the form of turbostratic birnessite with ~;10 percent trivalent manganese in the layers and probably ~;8 percent corner-sharing metal octahedra in the interlayers. The Zn is enriched on the rim of the nodule, associated with Mn. The Zn is completely (>90 percent) tetrahedrally coordinated and sorbed in the interlayers of birnessite on vacant layer Mn sites. The Zn and Mn species are similar to ones found in soils, suggesting common structural principles, despite the differing formation conditions in these systems.

        Cover page: Mn, Fe, Zn and As speciation in a fast-growing ferromanganese marine nodule
        • Article
        • Peer Reviewed
        LBL Publications (2018)
        We studied the distribution and speciation of Ce in a previously-characterized ferromanganese nodule from the South Pacific Gyre using X-ray microspectroscopy.We find Ce in three types of environment – diffusely in all parts of the nodule except the Fe-rich, Mn-poor “matrix”, fluorapatite grains with a negative Ce anomaly suggestive of an authigenic origin, and localized spots whose composition is consistent with a pseudobinary mixture of sorbed Ce4+ and a mix of sorbed Ce3+ and CeO2. In contrast with some other elements such as Ti, there is no clear correlation of the Ce concentration in the diffuse areas with either that of Mn, Fe or any linear combination of the two.We argue that the CeO2 came from oxidation of Ce3+ in the water column, while the Ce in the Mn-rich regions may have been initially deposited as Ce4+ and then partially reduced.
          Cover page: Forms and distribution of Ce in a ferromanganese nodule
          • Article
          • Peer Reviewed
          UCLA Previously Published Works (2020)
          Linear dichroism is an important tool to characterize the transmission matrix and determine the crystal or orbital orientation in a material. In order to achieve high-resolution mapping of transmission properties, the linear-dichroism scattering model in ptychographic imaging is introduced, and an efficient two-stage reconstruction algorithm is developed. Using the proposed algorithm on a uniaxial material, the dichroic transmission matrix can be recovered without an analyzer by using ptychography measurements with as few as three different polarization angles, with the help of an empty region to remove phase ambiguities.
            Cover page: Analyzer‐free linear dichroic ptychography
            • Article
            LBL Publications (2007)
              Cover page: Spectroscopic Evidence for Uranium Bearing Precipitates in Vadose Zone Sediments at the Hanford 300-Area Site
              • Article
              • Peer Reviewed
              LBL Publications (2016)
              Particle surfaces of mineral aerosols are important reaction sites in the atmosphere. Previous studies suggested that calcite in aerosols, which are emitted during dust periods, neutralizes sulfuric acid. In this study, depth-dependent X-ray absorption fine structure spectroscopy for individual particles was employed to determine calcium (Ca) species at particle surface and in the bulk ofindividual particles, using an X-ray microbeam measured in the conversion electron yield and fluorescence yield modes, which is a powerful method to understand chemical processes at aerosol surfaces.
                Cover page: Depth-dependent Calcium Speciation in Individual Aerosol Particles by Combination of Fluorescence Yield and Conversion Electron Yield XAFS Using X-ray Microbeam
                • Article
                LBL Publications (2008)
                  Cover page: Arsenic speciation in multiple metal environments: II. Micro-spectroscopic investigation of a CCA contaminated soil
                  • Article
                  LBL Publications (2008)
                    Cover page: Arsenic speciation in multiple metal environments: I. Bulk-XAFS spectroscopy of model and mixed compounds
                    • Article
                    • Peer Reviewed
                    Advanced Light Source (2018)
                    The transformation of cerium oxide nanoparticles (CeO2-NPs) in soil and its role in plant uptake is a critical knowledge gap in the literature. This study investigated the reduction and speciation of CeO2-NPs in barley (Hordeum vulgare L.) cultivated in soil amended with 250 mg CeO2-NPs kg-1 soil. Synchrotron micro-X-ray fluorescence (μXRF) was employed for spatial localization and speciation of CeO2-NPs in thin sections of intact roots at the soil-root interface. Results revealed that Ce was largely localized in soil and at the root surface in nanoparticulate form (84-89%). However, a few hot spots on root surfaces revealed highly significant reduction (55-98%) of CeO2-NPs [Ce(IV)] to Ce(III) species. Interestingly, only roots in close proximity to hot spots showed Ce uptake which was largely CeO2 (89-91%) with very little amount Ce(III) (9-10%). These results suggest that the reduction of CeO2-NPs to Ce(III) is needed to facilitate uptake of Ce.
                      Cover page: Cerium oxide nanoparticles transformation at the root–soil interface of barley ( Hordeum vulgare L.)
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