ATOMIC-RESOLUTION CHEMICAL-ANALYSIS USING A SCANNING-TRANSMISSION ELECTRON-MICROSCOPE

THE high angle elastic scattering of electrons in scanning transmission electron microscopy depends strongly on the atomic number Z, of the sample atoms, through the Z2 dependence of the Rutherford scattering cross-section1. The detection of scattered electrons at high angles and over a large angular range (75-150 milliradians) removes the coherent effects of diffraction, and the resulting incoherent image provides a compositional map of the sample with high atomic-number contrast1. If a fine electron probe is used, and the sample is a crystalline material oriented along one of its principal axes, individual columns of atoms can be imaged in this way2. Electrons scattered at low angles are not used in this detection scheme, and are thus available for simultaneous electron energy-loss spectroscopy3; in principle, this combination of techniques should allow the direct chemical analysis of single atomic columns in crystalline materials. Here we present electron energy-loss spectra from expitaxial interfaces between cobalt silicide and silicon, which confirm that atomic resolution can be achieved by this approach. The ability to correlate structure and chemistry with atomic resolution holds great promise for the detailed study of defects and interfaces.