Development of the EXELFS technique for high accuracy structural information

EXELFS (Extended Electron Energy Loss Fine Structure) spectroscopy contains the same local atomic structure information as XAFS in addition to having good low Z element sensitivity, much higher spatial resolution (nanoscale), and the capacity of combining other high spatial resolution TEM measurements. Due to poor quality of the EELS data, however, the EXELFS technique has not been developed to its full advantage. In this work, various new methods have been introduced to improve data acquisition technique and obtain now high quality EXELFS spectra. Also, the XAFS data analysis software has been interfaced to perform EXELFS data analysis at the same level of sophistication; this is a significant improvement over the previous cases. To develop EXELFS as a standard tool for structure determination, several additional problems must also be taken into consideration. Some of these are monitoring thickness variation, energy resolution variation, radiation damage during measurements, and better dark-current correction, as well as χ data renormalization. In this investigation, Al and SiC samples were used as calibration materials. Al K-edge, Si K-edge, and C K-edge EXELFS spectra were measured and analyzed using theoretical calculations and r-space non-linear least-squares fits to determine the structural parameters. Good agreement with the known structures was obtained.