atom-location by channeling-enhanced microanalysis, ALCHEMI

"Atom-location by channeling-enhanced microanalysis (ALCHEMI)" is a method that determines sites (locations) of impurity atoms in a crystal by utilizing a phenomenon where the incident electrons pass through specific atom sites (electron channeling). Sites occupied by impurity atoms can be distinguished from the intensity difference of characteristic X-rays (EDS spectra) observed at a small positive tilt angle and a small negative tilt angle from an exact Bragg condition, the tilt angle being adjusted by observing the electron diffraction pattern. In this method, EDS spectra are measured at two crystal orientations but recently, a more reliable technique has been prevailing. That is, a technique of two-dimensional rocking of the incident electron beam enables us to obtain patterns of characteristic X-ray intensities over a large angular range.

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