Défense de thèse de doctorat en sciences

Depth profiling of hybrid multilayers using ToF-SIMS: from model samples to photonic devices

Jury

Francesca CECCHET (UNamur), présidente; Laurent HOUSSIAU (UNamur), secrétaire; Yan BUSBY (UNamur); Anouk GALTAYRIES (Chimie Paris Tech); Laetitia BERNARD (EMPA, Suisse); Arnaud DELCORTE (UCLouvain).

Résumé

In diverse areas such as medicine, energy, aerospace or electronics, the technology around us is constantly growing in sophistication. To improve device performances, advanced materials are combined into thin films multilayers or complex 3D architectures.

At the same time, the search for miniaturization pushes the device features to dimensions in the nanometer range, which confers to interfaces a preponderant role in the macroscopic behavior of devices. The understanding of complex phenomena taking place at thin films interfaces is mandatory to identify degradation mechanisms and also to rationally prevent or limit these effects. Therefore, methods for in-depth characterization need to be developed to implement strategies and to guide both the design and the processing conditions of thin film stacks; this would finally allow increasing the device performance and lifetime.

In this context, time-of-flight secondary ion mass spectrometry (ToF-SIMS) has shown its ability to provide in-depth molecular information, combining an extremely high detection limit and surface sensitivity, high mass and depth resolutions, and convenient lateral resolution to image 3D features.

In this work, ToF-SIMS surface and depth profile analysis is applied to investigate model and applied thin film architectures using different analysis and erosion ion beams conditions. In particular, fundamental mechanisms of interaction with the surfaces are highlighted by varying the nature, energy and size of the ion beam projectile. The best analysis parameters to sputter organic and organic/inorganic hybrid thin films are then studied, allowing to limit the material modification induced by the ion beam exposition while maintaining intense and characteristic (high mass fragments) molecular signals and reasonable sputtering yields (analysis time).

On particularly challenging hybrid device architectures for OLEDs and solar cells applications, the results unambiguously show that low energy cesium ion beam (Cs+ at ~ 500 eV) and argon clusters ion beams (Arn+) with reduced size (n~500 atoms) at a relatively high energy (~20 keV) are the most suitable conditions to perform depth profile analysis.

 

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