A NEW METHOD OF THE IDENTIFICATION OF CRYSTALLINE-AMORPHOUS INTERFACES BY QUANTITATIVE EVALUATION OF HREM IMAGES. N.I. Borgardt and B. Plikat*, Moscow Institute of Electronic Technology, 103498 Moscow, Russia, *IV. Physikal. Institut der Universitat Gottingen, Bunsenstr. 13-15, 37073 Gottingen, Germany

Identification of the atomic structure of interfaces between amorphous and crystalline phases by quantitative evaluation of HREM-images of cross-sectional samples is not straight-forward. This is due to the fact that the projected potentials of the atoms in the amorphous layer overlap randomly if the distance between them exceeds the length of short range order (about 1,5 nm). As a result, the contrast of interface steps can be blurred to different extends.

Intensity fluctuations caused by the random overlap of the projected potentials of the atoms in the amorphous layer can be eliminated if the two-dimensional intensity distribution of a homogeneous region of the interface is averaged along the interface. A theoretical analysis shows that the shape of the intensity profiles obtained by this method depends on:

i.) the distribution of steps at the interface and

ii) the averaged distribution of the amorphous layer atoms in the vicinity of the crystal boundary atoms.

Properties of the interface structure can be obtained by comparison of theoretical and experimental intensity profiles for various defocus settings. In order to simulate stepped interfaces the EMS multislice program [1] was supplemented to take into account the short range order of the amorphous layer. For this purpose the averaged distribution of atoms in the amorphous layer as a function of the distance to the interface is calculated from the radial distribution function as obtained from X-ray or neutron scattering. Comparisons of experimental images of a c-Si/a-SiO₂ interface and simulations based on the proposed method were carried out.

1. Stadelman P.A. (1987) Ultramicroscopy 21, 131