In-situ observation of atomic processes in Xe nanocrystals embedded in al

Observation of nanometer-Xe clusters embedded in Al crystals

The structure of Xe precipitates with sizes in several nanometers embedded in Al is known to be stable and its structure is well confirmed. But knowledge about the structure of Xe precipitates with nanometer sizes is very limited. There are difficulties in observing such small structures embedded in a crystalline matrix. An off-Bragg condition is used to observe diffraction patterns, dark-field, and high-resolution transmission electron microscopy images. The structure of Xe precipitates with sizes of about 2 nm and smaller is observed and confirmed. They are in an fcc structure and their orientation relationship with the Al matrix is similar to that of larger crystalline Xe precipitates or in an undefined structure. The lattice spacing or atomic distance in such nanometer-sized Xe precipitates is smaller than those of larger Xe precipitates embedded in Al matrix. There is a trend that as the size becomes smaller, the precipitates are more likely to have an undefined structure.

High-angle annular dark-field STEM observation of Xe nanocrystals embedded in Al

High-angle annular dark-field scanning transmission electron microscope (HAADF-STEM) observation of Xe precipitates embedded in crystalline membranes has been made using electron probes of atomic dimensions and HAADF-STEM images of Xe precipitates qualitatively different from conventional TEM observation results have been obtained. Multislice-based HAADF-STEM simulation has been made and it has been revealed that the intensity of images of Xe atoms at positions displaced from Al matrix columns decreases rapidly as the thickness increases. Even in a thin specimen, the off-site Xe atoms of the precipitate at deep locations, were not observable. Therefore, different images are expected for specimens of different thicknesses or depths of these precipitates. These results indicate that the observation of precipitates in crystalline membranes requires some care.