EXELFS revisited: An improved data analysis technique

EXELFS (extended energy loss fine structure) spectroscopy contains unique information of local atomic structure, same as XAFS (X-ray fine structure), but has several advantages overXAFS, such as having high spatial resolution (nanoscale versus bulk), better low Z element sensitivity, parallel detectability, and no dependability on synchrotron-radiation-sources. Due to poor statistical total counts, however, EELS data quality is inferior and, therefore, EXELFS technique has not been well developed to its full advantages. The main limitations in EELS acquisition are channel-to-channel gain variations (CCGV) in the parallel detection system and low S/N ratio due to the instability of instrument that prevents long acquisition times. Techniques that circumvent CCGV, such as first or second difference, do not allow the retrieval of EXELFS signal from the spectra. Recently we have improved the EELS data acquisition technique so that CCGV could effectively be corrected and statistical fluctuations could reach a level much lower man that in the fine structure.