Fig. 1: In situ x-ray photoemission electron microscopy (XPEEM) investigation.
From: Absence of a pressure gap and atomistic mechanism of the oxidation of pure Co nanoparticles
a Schematic of the XPEEM setup for the in situ oxidation of Co nanoparticles by means of molecular oxygen dosing under ultrahigh vacuum (UHV) conditions. b–d Illustration of the samples under investigation: b Co nanoparticles on Si/SiOx wafers, c on electron transparent Si3N4-membranes covered with an amorphous carbon (a-C) layer, and d upon capping with an additional a-C layer for transfer to the high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) instrument. e XPEEM elemental and f respective x-ray magnetic circular dichroism (XMCD) contrast map of Co nanoparticles in the pristine metallic state on Si/SiOx acquired with the photon energy hν set to the Co L3 peak energy (the XMCD contrast ranges from ±0.025). The white arrow indicates the projected x-ray propagation direction. White circles indicate magnetically blocked (MB), dashed circles denote superparamagnetic (SPM) nanoparticles. The dark features are due to the saturated signal of lithographic gold marker structures used for sample navigation (scale bar is 3 μm). g Corresponding x-ray absorption spectra at the Co L3 edge. h HAADF-STEM micrograph of a Co nanoparticle preserved in the pristine metallic state by means of the a-C layers (scale bar is 5 nm). The inset displays an enlarged image of the highlighted region (scale bar is 1 nm).
