Contrast in the electron spectroscopic imaging mode of a TEM

Abstract

SUMMARY An energy‐filtering microscope working at 80 keV is used for the investigation of the effect of inelastic scattering on Bragg contrast. Inelastic scattering results in a preservation of Bragg contrast but edge and bend contours are blurred by a spectrum of excitation errors due to the angular distribution of inelastic scattering. This blurring and the chromatic aberration results in a decrease of contrast and resolution for thick specimens. Therefore, contrast and resolution can be increased by zero‐loss filtering as shown by evaporated films of increasing thickness below 150 μg/cm2. Up to ∼300 μg/cm2 an energy‐filtered image at the most probable energy shows the best results. The results obtained are extrapolated to energy‐filtered high‐voltage electron microscopy.

Energy-filtering transmission electron microscopy in materials science

“…However, the Lorentzian function of d03C3(03B8)/d03A9 decreases slowly at larger 0 up to the cut-off angle 03B8c (~ 6 mrad for Al) and a large fraction of inelastically scattered electrons contributes to the increase of the effective illumination aperture and the spectrum of excitation errors. The convolution of two-beam dynamical calculations of edge contours with the angular distribution (4) of plasmon losses qualitatively confirm this blurring effect [26,39].…”

“…Therefore, plasmon loss-filtering shows approximately the same Bragg contrast in edge and bend contours and lattice-defect images as zero-loss filtering in the bright-and dark-field modes. When plasmon-scattered electrons are selected with a small objective diaphragm near the primary or Bragg spots the same bright-or dark-field images can be observed, whereas zero-loss filtering of the thermal-diffusely scattered electrons show no Bragg contrast but only contrat by anomalous absorption effects because their intensity between the spots is proportional to the probability density 00* of the Bloch wave field near the nuclei [26]. Also plasmon-loss filtering between the spots only shows anomalous absorption effects and no Bragg contrast, because these electrons are predominately elastically and inelastically doublescattered.…”

“…When increasing the energy loss an increased blurring of the high-order bend contours and thickness fringes has been observed [26,[37][38][39][40][41]. This can be explained by the angular distribution of inelastic scattering, which becomes equivalent to a spectrum of excitation errors.…”

“…Anomalous transmission also allows to observe thicker single-crystal gold films [28]. The decrease of chromatic aberration by zero-loss filtering at 80 keV results in comparable images in a conventional TEM at 200 keV [29].…”

“…la (Fig. 4) figure 4 can be described by [26] with the mean absorption length of dynamical theory and the imaginary zero Fourier coefficient V0' of the lattice potential. These maximum mass-thicknesses of 150 p,gjcm2 are of the order of twice of those reported above for amorphous films.…”