Challenges in the characterization of complex nanomaterials with analytical STEM

Aberration corrected electron optics, novel detection techniques in combination with advancedcomputational capabilities have turned scanning transmission electron microscopy (STEM) intoone of the most powerful characterization techniques for a wide range of nanomaterials. Itsversatility stems from the availability of different imaging and diffraction modes as well asanalytical techniques such as electron energy-loss (EELS) and energy dispersive X-rayspectroscopy (EDX), which enables one to deduce information about structure, elementalcomposition and chemical bonding with atomic resolution [1]. This has paved the way for manybreakthroughs in understanding fundamental phenomena in physics, chemistry and materialscience in recent years.In practice, however, structural and chemical characterization on an atomic level, such as thedetection of impurities, dopants or point defects within a crystal, is often impeded by experimentalchallenges in sample preparation, limitations in signal-to-noise ratios (SNR), instrumentalinstabilities and the high current densities introduced by a highly focused electron beam. Thisleads to steady, yet often unrecognized specimen transformations [2], especially when applyingspectroscopic techniques, which in general require higher acquisition doses. This is particularlytrue for experiments that aim to determine concentrations or defects quantitatively [1, 3]. As aconsequence, many highly relevant material systems such as battery materials, materials with ahigh amount of low-coordinated surface atoms (nanoporous materials and nanoclusters) andorganic/biological materials, require the development of novel methodologies in preparation,characterisation and data analysis.The talk will give an overview over acquisition and analysis strategies for STEM spectroscopytackling the above-mentioned challenges by exemplary showcasing some selected researchquestions, with different material systems like complex oxides, metallic clusters and energymaterials.Exemplary, the column-by-column quantification of barium lanthanum ferrate and thecompositional characterization of Au@Ag and Ag@Au core-shell nanoclusters will be discussed.Emphasis will be placed on the use of direct detection detectors for EELS and complementaryhigh-sensitivity EDX.