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edfas.org 19 ELECTRONIC DEV ICE FA I LURE ANALYSIS | VOLUME 23 NO . 4 electron imaging and diffraction and the technologies developed for electron beam control can conceivably be utilized in a STEM-in-SEM setting. Although the current level of lens control (i.e., beam spot size, no post-sample lenses, and lack of aberration correction) does not enable atomic resolution imaging or some of the specialized imaging modes, STEM-in-SEM imaging capabilities are extensive andnot limited tobright-field (BF) anddark-field (DF) imaging. In cases where users require more beam positioning control or automation than included in the SEM software user interface, most SEM vendors offer an applicationprogramming interface (API) which can extend the beampositioning capabilities, and external scan gen- erators can also be implemented for even more control. For example, arbitrary scan patterns can be implemented to accommodate low-dose imaging techniques. Although the current state of the art in SEM beam control is good (Figs. 2a-c show how the beam can be adjusted to obtain different diffraction conditions), it is only amatter of time before free-lens control and aberration correction are offered on new SEMs. A major benefit of STEM-in-SEM is vacuum chamber size. Ample room is often available for in situ or operando experiments, custom sample holders, and detectors. [9-13] Several access ports to the vacuum chamber are gener- ally also available, and other sample manipulation and measurement tools can be added or removed depending on experimental requirements. Moreover, sample sizes are not limited to 3mmdiameter configurations. Electron transparent samples of nearly any shape or size can be used provided that the sample can be supported between the pole piece and transmission detector, and multiple samples can be loaded and analyzed for high throughput analysis with the appropriate holder. (continued on page 22) Fig. 1 AnSEMequippedwith two transmissiondetectors for imaging and diffraction. Fig. 2 Au (001) foil DPs. Inset green circles indicate the [020] reflection. The direct beam is located approximately at the center of each image. (a) A 30 keV DP obtained with CL ≈ 7.5 mm and underfocused beam (i.e., working distance = 50 mm for quasi-parallel illumination). (b) A 30 keV convergent beamDP with beam convergence angle a ≈ 10 mrad. (c) A 30 keV DP with illumination set to emphasize Kikuchi scattering. Spot patterns obtained using a 7.5mmaperture, CL ≈ 25mm, and beam energies of (d) 10 keV, (e) 20 keV, (f) 30 keV. Note the satellite spots and other fine details between kinematically allowed reflections. (a) (b) (c) (d) (e) (f)