Comparison between HRTEM and HAADF-STEM (Z contrast)

	HRTEM	HAADF-STEM
basics	interference of coherently scattered electron waves	incoherent scattering
recording method / time	parallel / 0.5 – 2 s	serial / 5-20 s (more problems with sample stability and drift)
cathode	LaB₆ or FEG	FEG
point resolution of a Tecnai F30 of a C_s-corrected microscope	ca. 2 Å < 0.5 Å	ca. 2 Å < 0.5 Å
obtainable information	atomic positions (and elemental distribution)	atomic positions and elemental distribution
image interpretation	comparison with simulations; at Scherzer defocus: atom columns dark	direct: atom columns always bright; intensity ~Z²

Example: WO₃ segregations in a niobium tungsten oxide


F30	HRTEM	HAADF-STEM

The positions of the metal atoms are recognizable in the HRTEM image recorded close to Scherzer defocus as dark dots while they always appear with bright contrast in the HAADF-STEM (Z contrast) image. The different brightnesses of dots in the Z contrast image indicate varying occupancies of the corresponding metal position by Nb and W (see: Krumeich, Nesper, J. Solid State Chem. 179 (2006) 1857-1863 DOI).

A useful introduction into theory and practice of TEM and STEM is given on the web site of Rodenburg.

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