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Séminaire PLUM

Jeudi 31 Janvier à 16h00
Salle Erwin Bertaut, F418

Orateur : Pierre Bordet, département PLUM
"Local structure of amorphous and crystalline VO2 thin films investigated by PDF analysis"


Pair Distribution Function analysis provides a quantitative multiscale description of the atomic arrangement whatever the material crystalline state, based on total scattering data. Due to experimental issues, only few PDF studies of thin films have been carried out until now. Here we show the possibility to obtain high quality thin film PDFs from moderately high energy synchrotron data recorded at the Cristal beamline at Soleil, using transmission geometry. We investigate the atomic structure of 200 nm-thick amorphous and crystalline VO2 layers. Due to the weak scattering signal from the thin films, special care was taken to minimize the contribution of the support material by using either a 50 μm-thinned down glass substrate or a 100 nm-thick monocrystalline silicon membrane. Three amorphous VO2 samples were investigated on each substrate : the pristine as-deposited layer, and two annealed variations of this material exhibiting a consistent change in resistivity. Additionally, a crystallized sample annealed at higher temperature was also measured. Surprisingly, PDF analysis revealed that the local structure of the crystallized sample is different from those of the three amorphous samples. Comparison of samples deposited on different substrates shows that the latter can have a large influence on the observed structure of the amorphous as well as crystallized phases, despite the presence of a SiN buffer layer.

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