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Images of Minerals at the Atomic Scale

Z-contrast and TEM Images from

Prof. Huifang Xu’s Research Group

Department of Geoscience, University of Wisconsin - Madison

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High-Resolution S/TEM at the University of Wisconsin

A high-performance FEI Titan scanning transmission electron microscope (STEM) with spherical aberration corrector. It can acquire images with <0.1 nm spatial resolution and has full analytical capability.

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Oxides: magnetite and Si-magnetite

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Luogufengite, maghemite, and hematite

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Lodestone

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Hematite and hydrohematite nano-crystals

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Goethite, Proto-goethite, and arsenic (As) adsorption

(A) a [010]-zone-axis Z-contrast image showing interface between proto-goethite and a stacking fault in goethite; (B) an FFT pattern from the selected area in A; (C) a noise-filtered image of the outlined area in A. The unit cell models of goethite along b-axis (left), and overlapped goethite and proto-goethite (center), and its stacking fault (right) are overlaid in the image. (American Mineralogist, 2016, in press)

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Polyhedral model of goethite (light ocher) and proto-goethite (brown) along [100]-zone-axis with their atomic models along [010]-zone-axis. (Highlight & Breakthrough paper of American Mineralogist, 2016)

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(A) a [001]-zone-axis Z-contrast image of proto-goethite, bright spots are positions of Fe atom columns. Very bright spots are As atoms on the surface right above Fe; (B) the intensity profile of an outlined area from X to Y; (C) the intensity profile of simulated Z-contrast image; (D) a simulated Z-contrast image; (E-F) Polyhedral models showing arsenate adsorption on (001) surface of the proto-goethite. (American Mineralogist, 2016, in press)

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Sulfides: pyrrhotite and monoclinic polymorph of greigite

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Carbonates: dolomite

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Carbonates: dolomite and “calomite” nano-mineral

Figure 8. Z-contrast image shows calcite exsolution lamellae //(001) in dolomite host. The line profile 1 has six consecutive Ca columns along (102) trace. The line profile 2 of the dolomite region shows the normal dolomite cation sequence of alternating Ca and Mg columns. The line profile 3 shows one repeat of d superstructure. The lines with arrows show the boundaries between calcite and dolomite and between dolomite and d superstructure. The atomic models for dolomite/calcite and dolomite/d phase interfaces are shown at the bottom. Carbonate group are not shown proportionally to highlight the cations. (Color online.)

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Figure 7. High-magnification bright-field (a) and dark-field (b) STEM images of d domains. Z-contrast (dark-filled) image shows that the Ca-rich precipitates have a cation sequence (bottom-right) of Ca-Ca-Mg-Ca-Ca-Mg- along c axis as opposed to dolomite cation sequence as shown in the middle-right corner (b). The occurrence of streaking and splitting along c* (i.e., d reflections) in the FFT patterns (bottom-left corner). 003 and 009 spots are from host dolomite, not from the d superstructure, because the position of 003 halfway between 002 and 004 of the d superstructure, and the position of 009 is halfway between 008 and 0010 of the d superstructure. Noise-filtered Z-contrast image (c) shows enhanced cation sequences in the d superstructure and dolomite host. Line profiles from line 1 (dolomite host) and 2 (d superstructure) also illustrate the ordering of Ca and Mg atoms. (Color online.)

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“Calomite’ is a nano-phase mineral occurs in Ca-rich dolomite. Its structure and composition is between calcite and dolomite.

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Carbonate: chukanovite

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Metals: Pt

Morphology mapping of platinum catalysts over the entire nanoscale

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Typical micrographs of platinum nanoparticles greater than ~5 nm, taken in STEM mode. Greater intensity indicates greater thickness (perpendicular to the beam), and facilitates shape analyses, though some particles do not show lattice fringes due to the off zone axis.

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STEM images showing (a) amorphous, non-crystalline Pt clusters, and (b) round (larger) Pt crystals. Note that the surface Pt on round crystals are less ordered (regular).