Quantitative Scanning Transmission Electron Microscopy: Counting Atoms in Nanoparticles

Here we present a quantitative scanning transmission electron microscopy (QSTEM) on a non-aberration corrected TEM/STEM, where the absolute intensity of the Z-contrast image gives the number of atoms in nanaoparticles (NPs). The true efficiency of the high-angle dark-field detector (HAADF) was measured from detector imaging, the response when using an electron beam scanning on the detector, at the actual electron beam trajectory through the complex of imaging lens system of the S/TEM.  The detector collection angle was calibrated with a STEM electron diffraction pattern from a Au (100) single crystal film, and the detector inner and outermost (half) angles are 100.3 and 252.1 mrad. Au NPs supported on ultra-thin carbon film or gamma alumina were produced via a UHV e-beam evaporator with sizes below 2 nm, were used for the test of this technique. We are currently developing this method for an aberration corrected STEM with the ultimate goal of 3-dimensional atomic tomography.