TRACE ELEMENTAL ANALYSIS AT NANOMETER SPATIAL-RESOLUTION BY PARALLEL-DETECTION ELECTRON-ENERGY-LOSS SPECTROSCOPY

Parallel-detection electron energy loss spectroscopy (EELS) combined w ith scanning transmission electron microscopy (STEM) and a field emiss ion source provides an unprecedented sensitivity for elemental microan alysis. By deflecting the energy loss spectrum across a parallel detec tor and computing the difference spectrum from sequentially collected energy-shifted spectra, the effects due to detector pattern noise are nearly eliminated so that signals less than 0.1% of the background can be readily detected. Measurements on a series of glass standard refer ence materials show that EELS provides both high spatial resolution an d trace sensitivity at the 10 atomic ppm level for a wide range of ele ments including the alkaline earths, 3-d transition metals, and the la nthanides. For analytical volumes with dimensions of the order of 10 n m, this translates into near-single atom detectability.