Conférence: The versatile family of molybdenum oxides: epitaxial flakes, gas sensors and oxide electronics

In the first part of this talk, the curious case of epitaxial growth of MoO2 onto c-plane oriented sapphire substrates is analysed. Density functional theory (DFT) calculation of the deformation energy allowed to predict the possible epitaxial relations of this heterostructure. To verify these predictions, MoO2/(001) Al2O3 were grown using the chemically driven isothermal close space vapor transport technique (CD-ICSVT). In the first stages of the growth, flakes both normal or parallel to the surfaces were observed. The composition and morphology of both types of flakes as well as the epitaxial relations of each were determined using transmission and scanning electron microscopies, x-rays pole figures, and Raman spectroscopy. They coincide with those predicted by DFT as the more favorable from the deformation energy point of view. For thicker samples, the flakes normal to the surface evolve to form a porous epitaxial film as a result of the coalescence of the flakes.

In the second part of the talk, it is presented the fabrication of MoO2/MoOx junctions by locally oxidizing the surface of a MoO2 film with a high-power pulsed laser.6 The junction presented a rectifying behaviour and the I-V characteristic was observed to be strongly dependent to the gases
exposure. This responds to a resistivity change of MoOx as a function of the used gas. This is an interesting effect that can be used for gas detection devices.