DETECTION AND QUANTITATIVE ASSESSMENT OF IMAGE ABERRATIONS FROM SINGLE HRTEM LATTICE IMAGES

For utilizing the full capabilities of quantitative high-resolution tr ansmission electron microscopy in materials characterization, a precis e knowledge of the various aberrations blurring the object information is essential. Here, we describe an extended approach to the detection and quantitative assessment of image aberrations from lattice images of crystal samples, The approach is based on a theoretical analysis of five-beam lattice images in the presence of all relevant optical aber rations and for partial beam coherence, Compact analytical expressions for linear and nonlinear image Fourier coefficients as explicit funct ions of the aberration parameters are derived. In particular, a fundam ental relationship between the occurrence of erroneous image symmetrie s and the simultaneous presence of optical misalignments and partial b eam coherence is established. An image analysis procedure is proposed which allows for the detection of even-and odd-order residual aberrati ons and for the quantitative determination of defocus, two-fold astigm atism and axial coma if the three-fold astigmatism is known. For coma- free images, the three-fold astigmatism can also be determined quantit atively. Moreover, the procedure allows for a reliable detection of cr ystal misalignment for images of wedge-shaped crystal samples.