EELS FINDS ATOMS

Abstract

RESEARCHERS in Japan have pushed to the single-atom limit the sensitivity of the chemical spectroscopy method called electron energy loss spectroscopy (EELS). The advance in EELS’s analytical resolving power provides scientists the ability to pinpoint in solids the locations of lone atoms such as impurities and identify them chemically ( Nat.Chem. , DOI:10.1038/nchem.282). In an EELS experiment, researchers irradiate a solid specimen with an electron beam and measure the element-specific decrease in beam energy (the energy loss) caused by interactions between the beam and sample atoms. Commonly used in conjunction with transmission electron microscopy (TEM), EELS can often reveal the chemical identity of atoms in the nanometer-sized area probed by the TEM beam. A standard way to boost the spatial resolution of both methods is to increase the beam energy (up to about 400 keV), which narrows the electron beam toward atomic dimensions. But therein lies a tradeoff: Raising the acceleration voltage focuses the ...