Oxidation and rapid reduction of supported organometallic precursors on silica yield large metallic particles (5 to 20 nm) that exhibit in transmission electron microscopy (TEM) a typical difference of contrast between the center and the borders. Z-contrast high angle annular dark field (HAADF) imaging in the scanning transmission electron microscope (STEM) has been successfully used to show that these particles are hollow in the case of Pd. PdMn particles have also been prepared and it is shown that they exhibit surface cavities instead of internal cavities.
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