ABSTRACT
Expressing annular dark-field scanning transmission electron microscopy (ADF-STEM) images on a quantitative absolute scale presents the experimentalist with a powerful opportunity for comparison with image simulations. Image simulations are natively expressed in the range from 0 to 100% of “fractional beam”. However, to obtain experimental data in these units detailed and careful calibrations are necessary. Some calibrations, such as magnification, are obvious; but other parameters, especially those relating to inhomogeneous ADF detector sensitivity or scanning distortion, require more careful consideration.
This chapter will discuss the approaches for experiment design and execution in the recording of high-fidelity quantitative ADF data. The dominant sources of error in both signal intensity and spatial precision will be explored from the most severe down to the more esoteric. While the focus will be on ADF imaging, many of the factors are also common to other imaging signals or even spectroscopy. The most common type of scintillator-photomultiplier ADF detectors will be discussed, along with their strengths and (several) weaknesses. With this, techniques to minimize the introduction of errors from these will be presented along with strategies for dealing with any residual errors. The emerging practice of reliable multi-frame imaging will be introduced, along with the benefits and new experimental opportunities it presents in electron dose or dose-rate management. Various tools will be discussed as well as their use in multi-frame image, or multi-pass spectrum-image, alignment.
