Quantitative Contrast Evaluation of an Industry-Style Rhodium Nanocatalyst with Single Atom Sensitivity.

Aberration-corrected electron microscopy opens new ways for material characterization. In catalyst research it will enable the observation of single atom arrangements, such as the location of promoter atoms on catalyst particles. However, quantitative procedures must be developed to account for dynamic contrast changes resulting from beam-sample interactions and incoherent instrument aberrations. We demonstrate that at low acceleration voltage (80 kV), for which knock-on damage is suppressed, the residual intensity fluctuations can be attributed to the presence of phonons resulting in 3D low frequency atom displacements. For rhodium [110] oriented particles it was found that the catalysts are platelets with an aspect ratio of about 0.2 and a surface roughness of ±1 atom. Observation of single surface atoms requires minimization of phonon-induced motion. The figure shows a high-resolution image of a [110] Rh nanoparticle on alumina recorded with sub-Ångstrom resolution at 80 kV (peak width at full width half maximum=75 pm). After performing a quantitative contrast interpretation and various calculations, it becomes possible to count the number of atoms in each column. The recorded [110] Rh particle is a platelet with an aspect ratio of about 0.2, an average column height of 4 atoms, and a surface roughness of ±1 atom. [ABSTRACT FROM AUTHOR]