Optimization of STEM tomography acquisition--a comparison of convergent beam and parallel beam STEM tomography.

In this paper two imaging modes in a state-of-the-art scanning transmission electron microscope (STEM) are compared: conventional STEM with a convergent beam (referred to as nanoprobe) and STEM with a parallel beam (referred to as microprobe). The effect and influence of both modes with respect to their depth of field are investigated. Tomograms of a human white blood cell (hemophagocytes) are acquired, aligned, and evaluated. It is shown that STEM using a parallel beam produces tomograms with fewer distortions and artifacts that allows resolving finer features. Microprobe STEM tomography is advantageous especially in life science, when semi-thin sections (approximately 0.5 microm thick) of biological samples are imaged at relatively low magnification with a large field of view.