ATOMIC RESOLUTION QUANTITATIVE COMPOSITION ANALYSIS BY ANNULA DARK FIELD STEM Z-CONTRAST EXPERIMENTS

In the last years High Angle Annular Dark Field (HAADF) experiments have received an increasing attention in the study of solid-state materials for the high spatial resolution, chemical sensitivity and flexibility to be used in combination with spectroscopic experiments at atomic resolution. Detailed information on the structure and the chemistry of the specimens can be achieved from a HAADF image even without any image simulation. , Moreover, quantitative chemical information do require the simulation of the experimental results. , Here a general approach to derive from the intensity distribution of a HAADF image the distribution of a chemical species in a host matrix is derived. As case study the method has been applied to measure at atomic resolution the composition profile of a Si layer buried in a GaAs matrix. The experimental images have been simulated by multislice method in the frozen phonon approximation. Due to the mainly incoherent nature of the HAADF image formation the partial occupation approach failed in the modeling of the alloy. Furthermore, it has been found that the atoms distribution in the column strongly influence the relevant HAADF intensity.