Toward Quantitative Annular Dark Field Imaging
Annular Dark Field imaging has the potential to be directly quantifiable. By this I mean that with careful measurement, the absolute image intensity has physical meaning. Unlike Bright Field TEM, the ADF image has no contrast reversals with focus and with the exception of thick specimens there are no contrast reversals with changes in thickness. Thus, image intensity is related to thickness, composition, orientation, and structure of local regions whose size is determined by the electron probe. The ability to extract quantitative information about the specimen from the intensity requires careful collection of the intensity data and a solid understanding of how that intensity will change with thickness, composition, orientation, and structure. The qualitative effect of thickness and composition has been well shown in the literature but more quantitative approaches have been lacking.The simplest models of ADF imaging treat each atom interacting