Application of FFT Data from HREM images to Electron crystallography

Abstract

We succesfully determined the 3D crystal structure of inorganic nano-crystalline material using fast fourier transform (FFT) data obtained from high-resolution electron microscopy (HREM) images. To extract the reliable structural information from nano-crystalline materials by HREM imaging, it is essential to minimize the dynamical scattering effects caused by interactions bewteen electrons and matters. To alleviate this restriction, we tried to solve the crystal structure by employing high voltage electron microscope (HVEM) which has excellent tilting capability, atomic resolution as well as higher penetration power. First, the allowed sample thickness for CaMoO4 crystal was evaluated by examining the existence of forbidden reflections in FFT data of HREM images obtained at various sample thicknesses. The kinematical scattering conditions were satisfied up to a sample thickness of about 28.2 nm. Second, we tried to extract the crystallographic data and determine the atomic structure of CaMoO4 crystal by FFT analysis of HREM images obtained from 15 different zone axes. Consequently, its cell parameters and space group were a = 5.24(3) A, c = 11.50(8) A and I41/a (#88), respectively. These values coincided with X-ray crystallography results within 0.002 ~ 0.080 A. Finally, the atomic structure could be determined with an accuracy of 0.16 A.