EELS log‐ratio technique for specimen‐thickness measurement in the TEM

Abstract We discuss measurement of the local thickness t of a transmission microscope specimen from the log‐ratio formula t = λ In (I t /I 0 ) where I t and I 0 are the total and zero‐loss areas under the electron‐energy loss spectrum. We have measured the total inelastic mean free path λ in 11 materials of varying atomic number Z and have parameterized the results in the form λ = 106F (E 0 /E m )/ln (2βE 0 /E m ) where F = (1 + E 0 /1,022)/(1 + E 0 /511) 2 , the incident energy E 0 is in keV, the spectrum collection semiangle β is in mrad, and E m = 7.6Z 0.36 . This formulation should allow absolute thickness to be determined to an accuracy of ±20% in most inorganic specimens.