Experimental method for determining Cliff-Lorimer factors in transmission electron microscopy (TEM) utilizing stepped wedge-shaped specimens preparedby focused ion beam (FIB) thinning

An experimental method to determine the Cliff-Lorimer factor has been devel oped utilizing an ultra-wide double-wedge (UWDW) FIB membrane geometry with terraced steps that increase in thickness in increments of approximately 3 0 nm. Pure elements are deposited as thin films onto a single-crystal Si su bstrate and energy dispersive X-ray spectroscopy (EDS) is performed on each of the terrace steps. The linear relationship that exists between X-ray co unts and specimen thickness can be established and the Cliff-Lorimer factor (k-factor) determined. This method for experimental k-factor determination can be used as an alternative to intimately mixed standards, when they are difficult to obtain. The following general relation was developed to deter mine the k-factor by this method: k(beta-alpha) = (m(alpha)/m(beta))(rho(be ta)/rho(alpha)) where m(alpha) and m(beta) are the slopes of X-ray intensit y vs. thickness plots for elements alpha and beta, respectively; and rho(al pha) and rho(beta) are the mass densities of elements alpha and beta. A pol ycrystalline Wi thin him on a single crystal Si substrate was used to test this method. The theoretical k-factor calculated for Wi and Si was k(Ni-Si) = 1.50. Two k-factors were determined for the UWDW membrane using the appr opriate microscope and detector conditions: k(Ni-Si)(Right) = 1.51 for the terrace steps to the right of the specimen membrane, and k(Ni-Si)(Left) = 1 .56 for the terrace steps on the left side. These results agree to within 0 .44% and 2.67%, respectively, of the calculated theoretical value. (C) 1999 Elsevier Science B.V. All rights reserved.