Foil thickness measurements in transmission electron microscope

Abstract

Methods for the in situ measurement of foil thickness in the transmission electron microscope (TEM) are reviewed for the non-specialist. The techniques described range from those based upon the analysis of crystallographic features contained in the specimen, as may be carried out with the most basic TEM configuration, to those which involve measurements of electron energy loss spectra or X-ray emission characteristics and require the addition of sophisticated analytical equipment to the electron microscope. Some methods are seen to give the foil thickness directly, while others must be regarded as being relative since they require calibration using reference foils of known thickness and composition. Factors such as the range of applicability, ease of use, and accuracy of the techniques are discussed as well as the possibility of misinterpreting the data.MSTj665

Determination of mean free path for energy loss and surface oxide film thickness using convergent beam electron diffraction and thickness mapping: a case study using Si and P91 steel

“…The determination of the thickness of a transmission electron microscope (TEM) specimen is an essential prerequisite for quantitative microscopy. A large number of methods have been devised for achieving this over the years (von Heimendahl, 1964; Hall & Vander Sande, 1975; Kelly et al ., 1975; Morris et al ., 1980; Allen, 1981; Berriman et al ., 1984; Egerton & Cheng, 1987; Scott & Love, 1987; Horita et al ., 1989; Egerton, 1996; Pozgai, 1997). Many of these methods have severe limitations, both in terms of the types of materials to which they can be applied and in their accuracy.…”

Thickness profiling of electron transparent aluminium alloy foil using convergent beam electron diffraction

“…(d) Absorption. Absorption causes a decrease in contrast in the CBED patterns contrast 5,12 . The absorption shifts the maxima in higher $$\Delta {\theta _i}$$ values and the minima in lower $$\Delta {\theta _i}$$ values.…”

“…The biggest effect is for the first minima/maxima 7,8 . Therefore, the biggest error comes from the measurement of the position of the fringe with the lowest $$\Delta {\theta _i}$$, which might be significantly displaced 12 . The absorption effect goes to nearly zero for the fringes located at highest $$\Delta {\theta _i}$$.…”

“…Absorption causes a decrease in contrast in the CBED patterns contrast. 5,12 The absorption shifts the maxima in higher Δ𝜃 𝑖 values and the minima in lower Δ𝜃 𝑖 values. The biggest effect is for the first minima/maxima.…”

“…In that case, Equation () is rearranged to 3 : $$\begin{equation}\left( {s_i^2 + \frac{1}{{\xi _g^2}}} \right)\;\;{t^2} = \;n_i^2,\end{equation}$$where $${s_i}$$ is the deviation parameter for each i th minima fringe from the exact Bragg condition, which is the position of the fringe at the centre of the convergent diffraction disks for which the deviation parameter s = 0, and n i is an integer number which we arbitrarily assign to each fringe. By dividing with $$n_i^2$$ on both sides and rearranging the Equation (), the following one is obtained 4,5,6,7,8,9,10,11,12,13 : $$\begin{equation}\;{\left( {\frac{{{s_i}}}{{{n_i}}}} \right)^2} = \; - {\left( {\frac{1}{{{\xi _g}}}} \right)^2}{\left( {\frac{1}{{{n_i}}}} \right)^2} + \;{\left( {\frac{1}{t}} \right)^2}.\end{equation}$$…”