In Situ Observation of ZnO Nanoparticle Formation by a Combination of Time-Resolved X-ray Absorption Spectroscopy and X-ray Diffraction

Abstract

The formation of ZnO nanomaterials from different Zn acetylacetonate precursor solutions was studied in situ by employing simultaneous, time-resolved X-ray diffraction (XRD) and X-ray absorption spectroscopy (EXAFS) at the Zn K-edge. The precursor solutions were heated from room temperature to the desired reaction temperatures in a hermetically sealed cell dedicated to X-ray experiments. In general, the first indications for the formation of hexagonal ZnO were found for elevated temperatures of about 80 °C both by XRD and EXAFS, and the contributions increase with temperature and time. However, no reaction intermediates could be proved in addition to the Zn precursors and the formed hexagonal ZnO materials. Furthermore, the results show that the efficiency of the reaction, i.e., the conversion of the precursor material to the ZnO product, strongly depends on the solvent used and the reaction temperature. ZnO formation is accelerated by an increased temperature of 165 °C and the use of 1-octanol, with a conversion to ZnO of more than 80% after only a ca. 35 min reaction time according to a detailed analysis of the EXAFS data. For comparison, an identical concentration of Zn acetylacetonate in water or dilute alkaline NaOH solutions and a reaction temperature of around 90 °C leads to a smaller conversion of approximately 50% only, even after several hours of reaction. The particle size determined from XRD for different orientations shows a preferred orientation along the c-direction of the hexagonal crystal system, as well in accordance with scanning electron microscopy. The LaMer model explained this highly non-uniform growth of needle-like ZnO crystallites.

Improving optical and morphological properties of Mn-doped ZnO via Ar ion sputtering followed by high-temperature UHV annealing

“…The findings of the XRD analysis are summarized in Table 2, which provides the position peaks (2θ • ), corresponding diffraction planes, and the corresponding d hkl interplanar spacing. Notably, these results demonstrate a high level of consistency with similar XRD studies conducted on Mn-doped ZnO films synthesized through spray pyrolysis [44][45][46][47][48][49].…”

X-ray Investigations of Sol–Gel-Derived GeO2 Nanoparticles

“…In the future, in situ investigations of the Ge-oxide formation processes are planned. As recently shown, a simultaneous combination of quick-scanning EXAFS and X-ray diffraction with a sub-second time resolution allows the following of crystallization processes in the liquid phase in large detail [57,58]. Thus, more information about the dynamics of the extremely fast GeO 2 formation processes may be obtained, and the preparation conditions for a tailored preparation of Ge oxides may be identified.…”