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Hetero‐contacts are interfaces between different materials at the nanoscale leading to novel functional properties. In hetero‐aggregates, primary particles of at least two different materials are mixed at primary particle or cluster level. Double flame spray pyrolysis (DFSP) is a versatile technique for the controlled synthesis of such materials. Characterization of hetero‐aggregates by scanning transmission electron microscopy (STEM) requires acquisition and evaluation of many aggregate images in order to derive statistically significant results. Usually, STEM energy dispersive X‐ray spectroscopy (EDXS) is used to acquire elemental maps providing the material distribution of the primary particles within hetero‐aggregates. However, the acquisition of a single EDXS map takes up to several minutes. For this reason, determination of material types of primary particles from the intensity in high‐angle annular dark field STEM images alone is desirable. These images can be acquired within a couple of seconds. In the present work, a method is suggested which allows for achieving this objective. It can be applied to distinguish materials with a significant difference in their atomic number and hence sufficient material contrast in the STEM images. [ABSTRACT FROM AUTHOR]

In hetero-aggregates, different materials form sintered hetero-contacts, which lead to new material properties. In this study, the influence of process parameters on the formation of hetero-contacts in Double Flame Spray Pyrolysis (DFSP) was quantified. The mixing of jets was monitored by Particle Image Velocimetry (PIV) measurements as well as by thermocouples and compared to the single flame setting. Overlap of the jets was evaluated using tracers to visualize the mixing zone. Ten CuO/CeO 2 model material samples were prepared with different flame inclination angles, nozzle distances and different particle volume fractions. Mixing on hetero-aggregate level was quantified using Convolutional Neural Network (CNN) evaluations of STEM images, Temperature-Programmed Reduction (TPR) and Differential Centrifugal Sedimentation (DCS) disk centrifugation to determine cluster sizes and hetero-coordination numbers as mixing quantifiers. Here, good correlations between the differently measured quantifiers were observed. [Display omitted] • Single-step synthesis of hetero-aggregates by gas phase mixing of different materials leading to hetero-contact formation. • Quantification of the mixing process of two aerosol-laden jets with respect to gas velocity, temperature, and tracer mixing. • Quantification of mixing quality on hetero-aggregate level in a CuO/CeO 2 model material • Cluster sizes, hetero-coordination numbers, mobility equivalent diameters, and material reducibility as mixing quantifiers. [ABSTRACT FROM AUTHOR]