“Hetero-contacts in functional oxide aggregates: Descriptors of heterogeneity, aggregate design and process simulation towards nanostructured optical precursor materials” 

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The present project targets the generation, mechanistic understanding and process model implementation of hetero-contacts in inorganic oxide particle aggregates derived through gas-phase processing. A further focus is on the specific material functionality resulting from such hetero-contacts in the context of particle-based precursors and green bodies for optical and photonic applications. In the first funding phase, special attention will be given to two types of hetero-contacts: contacts between oxide particles of variable chemical composition (hetero-chemical contacts) and contacts between oxide particles of variable atomic structure, in particular, crystalline and amorphous particles of equivalent chemical composition (hetero-structural contacts). We expect comprehensive interfacial design on aggregate level to provide unique opportunities in the fabrication of functional materials in two regards. First, exploiting hetero-contacts for tailoring post-processing routes (e.g., sintering ability, triggering or suppression of interfacial reactions, contact transport reactions) is assumed to enable new routes towards as to yet inaccessible material properties, for example, in the combination of assumedly incompatible material chemistries. Secondly, gas-phase aggregation of heterogeneous material formulations is a basic requirement for the manufacture of bulk optical materials with controlled nanoscale heterogeneity beyond the limits of direct (liquid-phase) doping. Both of these aspects require fundamental consideration and a particular degree of interdisciplinary insight such as offered in the scope of the priority program 2289, to which we are addressing this proposal. 

We will initially aim for comprehensive analytical protocols which enable the characterization and mechanistic understanding of the functionality of nanoscale oxide aggregates towards the design of specific material functions based on hetero-contacts. In particular, this is to connect the understanding of non-linear mixing effects on the level of material properties (the fundamental role of the contact) with a process framework and engine for dedicated aggregation strategies (based on process understanding and simulation tools). Adjusted particulate structures will be prepared by means of coaggregation using jet injection assisted by atmospheric microwave plasma treatment. While targeting universal applicability of tools and understanding, we will start from the example of heterogeneous particle aggregates of rare-earth doped silica and alumina nanoparticles. These do not only offer the specific application context, but also enable optical tracking of contact formation and evolution. They may thus act as model systems for a wider range of solid aggregates and aggregate formation in gas phase.