The design of nanoparticles (NPs) with dedicated material properties relevant for specific applications relies on a fundamental understanding of the underlying (trans-)formation mechanisms. Combining experimental observations during particle formation with corresponding simulations offers mechanistic insights necessary to optimize particle characteristics. Chemical vapor synthesis (CVS) is a gas-phase NP synthesis technique enabling scalable production of NPs with desired characteristics. The time–temperature, T(t), profile of the CVS reaction mainly governs the (trans-)formation of NPs. Ex situ investigations to determine correlations between process parameters and particle characteristics often suffer from information loss due to aging or oxidation of transient species, aggregation, or preferred orientations of nanocrystals. These discrepancies may be avoided by in situ and operando probing: where and while the particles are formed. Here, we report results on in situ X-ray diffraction of tin oxide (SnO2) NPs during CVS using synchrotron radiation to observe the evolving crystal structure as the particles form and grow. Especially, the influence of the T(t) profile on the crystal structure of NPs is investigated in situ. Experimental results are complemented by simulations using a physicochemical model of the CVS process. Combining in situ and operando experiments with simulations uncovers the underlying (trans-)formation mechanisms and indicates a dynamic evolution of NP structures. Additionally, temperatures of the nanocrystals in the CVS process are determined by Rietveld refinement of the in situ and operando XRD data via thermal expansion of the lattice parameters.
Joshi et al. (Wed,) studied this question.
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