Formation of Aluminum‐Doped Zinc Oxide Nanocrystals via the Benzylamine Route at Low Reaction Kinetics

Abstract

The influence of essential process parameters on the adjustability of specific process and particulate properties of aluminum-doped zinc oxide (AZO) nanocrystals during synthesis via the benzylamine route at low reaction kinetics is demonstrated by enabling time-resolved access of the selected measurement technique. It is shown that the validity of the pseudo-first-order process kinetics could be extended to the minimum operable reaction kinetics. On the other hand, the impacts of the process temperature and the initial precursor concentration on both the process kinetics and the particle morphology are discussed. The obtained data provide a versatile tool for precise process control by adjusting defined application-specific particle properties of AZO during synthesis.

Evaluation of the Dispersion Stability of AZO Mesocrystals for Their Processing into Functional Thin Films Using Small Angle X-ray Scattering

“…The presence of the third structural level, which was originally assigned to the aggregate structure in Section 3.1, is no longer detectable for the stable phase in Figure 4, indicating a successful steric stabilization of the system at the mesocrystal level . Obviously, the stabilization at the primary crystal level could not be achieved due to irreversible adhesions and intergrowth during synthesis, as expected and reported in our previous works [16,17]. Possibly, the intergrowth of the primary crystals into highly-ordered, regularly shaped hexagonal mesocrystals, having a high aggregation density with ( ) = 2.7, could have a positive effect on the particle occupancy density and thus on the application properties of the final thin films (e.g., lower interfacial resistances), since a comparable density could probably not be generated by selfarrangement of stable particles during the coating and drying processes by stabilization at the primary crystal level alone.…”

“…The TEM image in Figure 2a is used to assign the structural parameters of the various levels from the Unified-Fit model obtained with SAXS to the actually existing particle structures of the examined non-stabilized AZO nanocrystals. Figure 2a shows hexagonally shaped mesocrystalline particle structures of AZO (solid line) with remaining internal grain boundaries (dashed line) arising due to non-classical crystal growth with oriented agglomeration processes during the synthesis process, as we reported previously [16,17]. Here, the mesocrystals are arranged in superordinate aggregate structures with clearly visible phase boundaries, resulting in an average mesocrystal size of d 50,TEM = 29.5 nm(±19%) from a statistical imaging evaluation of approximately 200 mesocrystals using TEM under the assumption of spherical particles.…”

“…The endothermic synthesis was ended by quenching the particle growth after 120 min by rapid cooling in a water bath. To remove the organic reaction medium from the particle surface necessary for the subsequent stabilization process, the AZO nanocrystals were purified after the synthesis by repetitive centrifugation and dispersion processes and were finally presented in an ethanol-based dispersion, as described in detail in our prior works [16,17].…”

“…For this purpose, small-angle X-ray scattering (SAXS) as a non-invasive measuring method basically offers the possibility of recording and correlating structural properties in each individual process step independently of the state of the nanoparticles (e.g., powder, dispersion, or thin film) [13][14][15]. In the course of our own previous work, the synthesis of AZO nanocrystals via the benzylamine route could be comprehensively clarified using X-ray scattering analysis methods, on the one hand, by developing a growth model covering the time-resolved growth to hexagonal-shaped mesocrystalline nanoparticles [16] and, on the other hand, by investigating influences of important process parameters on the growth behavior at low reaction kinetics [17].…”

Genetic Parameterization of Interfacial Force Fields Based on Classical Bulk Force Fields and Ab Initio Data: Application to the Methanol-ZnO Interfaces

“…On the one hand, CH 3 OH is not only one candidate to be a green liquid fuel in the future, but it is also used to characterize the reactivity of surfaces from oxide materials since it takes part in various catalytic reactions . On the other hand, the application range for ZnO is wide, e.g., it is used as a material for gas sensing, for nanoparticles, for microelectronic devices, or as a catalyst in catalytic reactions . The interaction of both materials is a current topic of interest due to their applications during an industrial methanol synthesis or a synthesis of ZnO nanoparticles with different morphologies .…”