IMPROVEMENTS IN DETECTION SENSITIVITY BY SPATIAL DIFFERENCE ELECTRON-ENERGY-LOSS SPECTROSCOPY AT INTERFACES IN CERAMICS

Many problems in materials science require that a small amount of an impurity is detected; for example the segregation of such an impurity to an internal interface. For such inhomogeneous specimens two electron energy-loss spectra can be recorded: one from the interface and one from the nearby matrix. The second spectrum serves as a reference and can be subtracted from the first to remove the background and to reveal the excess of an element at the internal boundary. This method is labelled ''spatial difference''. In this paper spatial difference is compared to other methods of background removal in electron energy-loss spectra. After a general discussion of the methods their detection sensitivity is compared quantitatively by calculating the signal-to-noise ratio with a simple numerical model. The results are compared to experimental results for the detection of Ca at grain boundaries in alumina and N inclusions in diamond. It is found that spatial difference has the highest signal-to-noise ratio in these model experiments and therefore improves the detection sensitivity as compared to the other methods. Spatial difference of inhomogeneous specimens in a scanning transmission electron microscope is straightforward. A clear advantage of the spatial difference involves the study of near-edge structure of the impurity element, yielding information on the atomistic structure and chemical bonding of internal interfaces.