Abstract
Non-stoichiometric ceria nanoparticles (NPs) were obtained by a gas aggregation source with a magnetron and were mass-selected with a quadrupole mass filter. By varying magnetron power, Ar gas flow, and the length of the aggregation tube, NPs with an average diameter of 6, 9, and 14 nm were synthesized and deposited onto a substrate, thus obtaining NP films. The morphology of the films was studied with scanning electron microscopy, while high resolution transmission electron microscopy was used to gain a deeper insight into the atomic structure of individual NPs. By using X-ray photoelectron spectroscopy we analyzed the degree of reduction of the NPs of different diameters, before and after thermal treatments in vacuum (reduction cycle) and in O2 atmosphere (oxidation cycle) at different temperatures. From this analysis we inferred that the size is an important parameter only at intermediate temperatures. As a comparison, we evaluated the reducibility of an ultra-thin ceria film with the same surface to volume ratio as the 9 nm diameter NPs film, observing that NPs are more reducible than the ceria film.
Highlights
The main property of cerium oxide that attracts scientific attention is its ability to store and release oxygen depending on the ambient conditions [1]
The aim of this work is to investigate the fundamental relationship between NPs chemical and physical properties, in order to improve the understanding of the basic processes, which are fundamental for the ceria NPs applications
After a thermal treatment at 1020 K, these differences in the Ce3+ component intensities are less significant; in agreement with the results reported in [27], the oxygen vacancy formation energy is related with NPs size, in particular it decreases with increasing the NPs size
Summary
The main property of cerium oxide that attracts scientific attention is its ability to store and release oxygen depending on the ambient conditions [1]. With the assumption that the increase of the lattice parameter is due to a higher concentration of oxygen vacancies, Tsunekawa results are complementary with the ones of Zhou et al [7], obtained for NP diameters between 4 and 60 nm. These results led to the conclusion that the lattice parameter increase is related to the formation of oxygen vacancies and Ce3+ ions
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