Flash evaporation of low volatility solid precursors by a scanning infrared laser

Abstract

The steady and stoichiometric delivery of metal-organic precursor mixtures is essential for the production of complex, functional nanomaterials in the gas phase. Chemical vapor synthesis (CVS) is a corresponding process which enables the production of complex oxide nanoparticles such as perovskites. While there exist a vast number of compositions that form perovskite structures, many technically relevant materials consist of transition metals and lanthanides. Their corresponding metal organic precursors often deviate significantly in their thermal behavior, resulting in a challenging delivery of precursors to the reactor. One suitable method for precursor delivery is flash evaporation by an infrared laser, where a mixture of solid precursors is instantly sublimed. Using flash evaporation, the stoichiometry of the generated vapor corresponds to the composition of precursors in the solid mixture. In this study, we present an alternative flash evaporation system based on a marking laser which rapidly scans a focused infrared beam across a precursor powder bed. By focusing the beam, higher energy densities are reached, compared to existing systems while a large area powder bed is repeatedly scanned and sublimed. Fourier-transform infrared spectroscopy (FTIR) measurements confirm the decomposition-free sublimation of precursor mixtures. Furthermore, we confirm the successful precursor delivery by the synthesis of LaFeO3 nanoparticles with an average crystallite size of 5.3 nm. The structure of the ensemble of nanoparticles is examined using X-ray diffraction (XRD) and Rietveld refinement, transmission electron microscopy (TEM), selected area diffraction (SAED), and extended X-ray absorption fine structure (EXAFS) at the Fe-K edge analyzed by reverse Monte Carlo (RMC) analysis.

LaCo1–xFexO3 Nanoparticles in Cyclohexene Oxidation

“…Chemical vapor synthesis (CVS) is a gas-phase process that produces ensembles of nanoparticles with significant fractions of surface atoms in the size region of 5 nm and well-defined structural characteristics. The process also allows the synthesis of complex oxides such as lanthanum-based perovskites, e.g., LaGaO 3 or LaFeO 3 − nanoparticles. In the perovskite formula A III B III O 3 , the A-site is typically occupied by a lanthanide ion, while the occupancy of the B-site is variable over a wide range of elements.…”