Composition evaluation by the lattice fringe analysis method using defocus series

The present paper deals with an extension of the composition evaluation by lattice fringe analysis (CELFA). The procedure is applied to an InxGa1−xAs/GaAs(0 0 1) Stranski–Krastanow heterostructure capped with 10 nm GaAs. CELFA is based on images obtained with a three-beam condition of only three excited reflections. Their interference produces a fringe pattern in the image plane. Under appropriate imaging conditions, the contrast pattern strongly depends on the In-content. CELFA uses the amplitude ratio |I0 0 2|/|I0 0 4| of the (0 0 2)- and (0 0 4)-reflections of image cell diffractrograms, which is an approximately linear function of the In-content x. In this paper an extension of CELFA will be introduced that is based on a defocus series instead of only one single image. All free parameters of the image formation are directly derived from the defocus series with a simple procedure. Therefore, the extended CELFA procedure does not require any knowledge concerning the imaging conditions (except the sample orientation). Furthermore, we will show how the effect of locally changing imaging conditions across the HRTEM image can be taken into account.