Spatial resolution and radiation damage in quantitative high-resolution STEM-EEL spectroscopy in oxides

The chemical analysis on the atomic scale in a scanning transmission electron microscope bears a number of challenges. These are an unambiguous assignment of a spectroscopic signal to a sample location and sufficient signal above noise for quantification. Modern aberration-corrected optics provide intense electron probes allowing for the highest spatial resolution and beam current density possible. On the other hand, non-destructive analysis requires low irradiation doses, so that there is a limit to the achievable signal-to-noise ratio. Here, we employ the StripeSTEM method that sacrifices the resolution in one spatial dimension in return for decreased radiation damage to the sample. Using this technique, radiation damage effects and achievable quantification accuracy are examined on the example of bulk SrTiO3 and a one unit cell thick layer of LaAlO3 in SrTiO3. The results show that valency artefacts are expected for conventional recording conditions where the electron dose is concentrated to a few atomic columns. Likewise a high accuracy for measuring the oxygen defect chemistry without radiation damage requires spreading out the irradiation dose.

► STEM EELS quantification accuracy is discussed against the background of radiation damage. ► Quantitative data is shown for a SrTiO3/LaAlO3 oxide heterointerface. ► A high-resolution acquisition procedure that distributes the electron dose is applied. ► Cation intermixing and defect chemistry are evaluated, methodological limits are discussed.