0.12 nm resolution in HAADF experiment performed by conventional 200KV FEG TEM/STEM microscope

High angle annular dark field (HAADF) imaging is a powerful tool to investigate the structure and the chemistry of solids with atomic resolution. In fact, HAADF images give structural information with an achievable resolution of , where is the spherical aberration coefficient of the objective lens and is the electron wavelength, and hence intrinsically higher with respect to the resolution of phase contrast high-resolution experiments (HRTEM) with the same , and at optimum defocus. Furthermore, the HAADF image intensity is proportional to , where Z is the atomic number of the species contained in the observed atomic column, and , which depends also on the atomic specie, is a number close to 2. As a consequence, the HAADF image contains a strong information on the chemical species in the specimen and can be used to detect individual atoms, or to measure at atomic resolution the profile concentration, of a specie in a host matrix. , Since few years ago, to obtain atomic resolution HAADF results, dedicated STEM equipment were necessary. More recently high quality HAADF experiments can be obtained on modern field emission gun (FEG) TEM microscope equipped with scanning unit and HAADF detector. Here, a resolution of 0.12±0.01nm in HAADF experiments has been achieved in the study of supercell formation after annealing of GaAsN epilayer grown on (001) GaAs substrate. TEM experiments were performed at room temperature using a JEOL 2010F UHR TEM/STEM field-emission gun electron microscope, operating at 200 kV with a measured Cs = 0.47±0.01 mm and equipped by HAADF detector.