Richard Mayet

Electrical and optical properties of vanadium dioxide containing gold nanoparticles deposited by pulsed laser deposition

Nanostructured vanadium dioxide is one of the most interesting and studied member of the vanadates family performing a reversible transition from an insulating state to a metallic state associated with a structural transition when heated above a temperature of 68 C. On the other hand, noble metal nanoparticles (NPs) support localized surface plasmon resonance which causes selective absorption bands in the visible and near-IR regions. The purpose of this letter is to study structural, optical, and electrical properties of vanadium dioxide thin films containing gold nanoparticles synthetized using pulsed laser deposition process. Thus, we have performed x-ray diffraction, optical transmission, and four point probe electrical measurements to investigate the nanocomposite properties versus its temperature. Interestingly, we have observed switching behavior for VO2 film containing gold NPs with a resistivity contrast of four orders of magnitude and a decrease of its transition temperature

Structural and electrical properties of large area epitaxial VO2 films grown by electron beam evaporation

Large area (up to 4 squared inches) epitaxial VO 2 films, with a uniform thickness and exhibiting an abrupt metal-insulator transition with a resistivity ratio as high as 2.85 × 10 4 have been grown on (001)-oriented sapphire substrates by electron beam evaporation. The lattice distortions (mosaicity) and the level of strain in the films have been assessed by X-ray diffraction. It is demonstrated that the films grow in a domain-matching mode where distortions are confined close to the interface which allows to grow high-quality materials despite the high film-substrate lattice mismatch. It is further shown that a post-deposition high-temperature oxygen annealing step is crucial to ensure the correct film stoichiometry and provide the best structural and electrical properties. Alternatively, it is possible to obtain high quality films with an RF discharge during deposition, which hence do not require the additional annealing step. Such films exhibit similar electrical properties and only slightly degraded structural properties.

A nitriding process of very thin molybdenum films in an expanding microwave plasma at low temperature

A transfer of nitrogen of about 20 at % is detected in very thin molybdenum films of about 200 nm thick coated on Si (100) wafers heated at 673 K and exposed to ternary (Ar-N2- H2) plasma. The nitrogen diffusion goes with a noticeable decrease of the remaining oxide layers in the whole film thickness. On the contrary, pure N2 gas exposure leads to a slight diffusion of nitrogen into the first molybdenum layers up to a depth of about 40 nm, only and an enhancement of oxygen amount also. Hydrogen species contained in the plasma reduce the oxide layers which act as nitrogen diffusion barrier. The nitrogen diffusion decrease with increasing distance of the workpiece surface from the centre of the discharge as well as the occurrence of nitrogen diffusion in molybdenum layers at room temperature highlight the role of NHx<3 active species of the plasma on the reactivity of the surface. The morphology of the nitrided surface consists of slightly smaller grains compared with those corresponding to untreated molybdenum films ranging in size from 30 to 50 nm wide. In contrast to substrates heated at 873 K, the tetragonal Mo2N structure has not been detected in molybdenum films heated at 673 K.