Themis3 300

The HR-STEM in high-angle annular dark-field (HAADF) mode and STEM-EDX (referred to as EDX in the text) analyses were performed using a double aberration-corrected FEI Titan Themis³ 300 transmission electron microscope equipped with a Super-X EDX detector and operated at an acceleration voltage of 300 kV. The analyses were carried out at a convergence angle of 15.7 mrad, a dwell time of 50 μs and a screen current of around 200 pA. For all three compositions, at least six nanoparticles were analyzed in at least two independent EDX maps. The evaluations were performed using Velox version 3.0.0.815 software from Thermo Fisher Scientific, with background correction and fitting of the respective elements. To determine the molar content, the arithmetic mean of each element of the measured particles was calculated with the corresponding standard deviation. Prior to the experiments, the alloy NPs were washed with and re-dispersed in Millipore water. Next, the sample dispersion was dried on an ultrathin carbon film on a Lacey carbon support film copper TEM grid, 400 mesh (Ted Pella, Inc.) and cleaned in a Fischione Model 1020 plasma cleaner, with a gas mixture of 75% argon and 25% oxygen, for 10 seconds.