posted on 2024-01-11, 22:30authored byAndrea Macrelli, Alessio Lamperti, David Dellasega, Valeria Russo, Carlo S. Casari, Andrea Li Bassi
Nanostructured
manganese oxide thin films with different crystallinity
and nanomorphology were synthesized by pulsed laser deposition (PLD)
in oxygen gas. Through grazing-incidence X-ray diffraction during
postdeposition thermal annealing in oxidizing (air) or inert (N2 flux) atmospheres, phase changes, crystallization onsets,
and orientation effects were evaluated between room temperature and
600 °C, revealing a significant impact of growth conditions and
nanoscale morphology on the X-ray patterns. Compact nanocrystalline
Mn3O4 films underwent first crystallization
improvement between 300 and 485 °C accompanied by unit cell shrinkage,
then phase transition to α-Mn2O3 above
500 °C in an oxidizing environment. In contrast, during annealing
under N2 flux, crystalline Mn3O4 was
stable up to 600 °C, maintaining the preferential orientation
promoted by PLD. Similarly, nanoporous amorphous MnO2 films
crystallized to α-Mn2O3 (>480 °C)
and Mn3O4 (∼385 °C) in oxidizing
and inert atmospheres, respectively; however, the amorphous porous
morphology led to poorer crystallinity and an isotropic, powder-like
crystal orientation. Quantitative analysis of structural parameters
in the whole temperature range and microscopic and Raman analyses
complemented the results. These findings shed light on the structural
stability and nanoscale design achievable by PLD, followed by suitable
annealing, of materials relevant for several technological applications.