Analysis of diffraction contrast as a function of energy loss in energy-filtered transmission electron microscope imaging

The relationship between diffraction contrast and electron energy loss was investigated by obtaining energy-filtering transmission electron microscope images of a bend contour in aluminum in 100 eV increments from 0 to 1000 eV. Results show that: (i) the relationship is an exponentially decaying function which becomes approximately zero at 1000 eV under the experimental conditions employed, (ii) there is a large influence of diffraction contrast on energy-filtered images (EFI), and particularly jump-ratio images, out to several hundred eV energy loss, (iii) while blurring of diffraction contrast in EFI is due to the increase in the characteristic scattering angle of inelastic electrons associated with an increase in energy loss, the intensity of diffraction contrast in EFI is proportional to the total image intensity, and (iv) diffraction contrast does not become negligible in EFI acquired at increasing energy loss until the image is noisy and contains little usable signal, indicating that diffraction contrast is always present to some degree in EFI. This can be attributed to plural scattering since high-angle Bragg (elastic) events redistribute inelastic signal in the diffraction plane outside of the collection aperture. Finally, a dynamical two-beam calculation is presented that describes diffraction contrast in EFI as a function of both tilt parameter and energy loss for comparison with the experimental results. (C) 1999 Elsevier Science B.V. All rights reserved.