Grazing Incidence Fast Atom Diffraction in high-pressure conditions : from collisional decoherence to real-time characterization of thin-film growth by HiPIMS.

Real-time characterization of thin film growth is a major issue because the growth parameters largely predetermine the properties of the film. This is particularly challenging in the case of film deposition by magnetron sputtering (MS) where the presence of electromagnetic fields near the substrate makes high energy electron diffraction (RHEED) ineffective. To date, there is no simple laboratory approach to monitor thin film growth by MS and obtain real-time information on growth mode, crystallographic properties, lattice orientation, etc.
This work focuses on the development and validation of a new tool for characterizing surfaces and thin layers in a high pressure environment (beyond 10^-4 mbar) using Grazing Incidence Fast Atom Diffraction (GIFAD). GIFAD is an extremely surface sensitive and non-destructive technique, considered as a complement/alternative to RHEED. It is used to monitor in real time the growth of thin films from ultra-high vacuum up to approximately 10^-6 mbar.
The first part of the work is dedicated to the implementation of a new device, HP-GIFAD, allowing operation at higher pressures. A compact solution with double differential pumping, which preserves the beam coherence and a good signal-to-noise ratio on the detector, allows HP-GIFAD to operate up to 10^-2 mbar (1 Pa) of Ar.
The second part investigates the fundamental properties of the beam diffracted by the surface and propagating in the high pressure zone. A decoherence induced by the interaction of the wave packet with the surrounding Ar atoms could be quantified ; it is associated with an anomalous narrowing of the Bragg peaks that strongly depends on the coherence width of the primary beam.
The last part of the thesis focuses on the compatibility of HP-GIFAD with thin film deposition by high-power impulse magnetron sputtering (HiPIMS), a variant of MS. Pulsing the detector, in anti-synchronization with the plasma pulse, makes it possible to significantly reduce the effect of particles, identified as metastable atoms produced by the plasma, on the detector. Thus, from a technical point of view, HP-GIFAD is fully compatible with HiPIMS. Preliminary results on the growth of Cu films on an insulating substrate indicate an island growth ; further adjustment of the HiPIMS parameters (pulse power and duration, ion acceleration, Ar pressure, etc.) should favor a layer-by-layer growth mode.