Quantitative annular dark-field STEM images of a silicon crystal using a large-angle convergent electron probe with a 300-kV cold field-emission gun

Annular dark-field scanning transmission electron microscope (ADF-STEM) images of an Si (001) crystal were obtained by using an aberration-corrected electron microscope, at 30-mrad convergent probe and cold field-emission gun at 300 kV. The intensity of ADF-STEM images, that is, the number of scattered electrons relative to the incident electrons, obtained for specimen thickness from 10 to 50 nm was compared quantitatively with absorptive multi-slice simulation. The column and background intensities were analyzed by column-by-column two-dimensional Gaussian fitting. These intensities were found to increase linearly with the sample thicknesses. However, the simulated image gave higher column intensity and lower background intensity for all the sample thickness. We found that experimental images were reproduced by the simulation with Gaussian convolution of 70 pm full-width at half-maximum for all the sample thicknesses from 10 to 50 nm. The possible factors accounted for this Gaussian convolution is discussed.