Thesis Topic: Study of the Impact of UV Radiation on Contaminant Morphology through Photofixation: Molecular Mechanisms and Characterization Protocol

Exposure to ultraviolet (UV) radiation in orbit can induce photopolymerization phenomena, which significantly amplifies surface contamination by initially volatile species. Previous work conducted as part of CNES-ONERA theses in the early 2000s (A. Pereira, 2001–2004; M. P. Nghiem, 2006–2009) identified generic accretion mechanisms, such as UV activation of surfaces or contaminants and competition between desorption and chemisorption. However, these studies were limited to global characterization of deposits (total mass), which did not allow for precise confirmation at the molecular level. Furthermore, no robust protocol has been established to identify the chemical species involved and the parameters controlling them. A. Zamo's thesis demonstrated that the morphology of contaminants depends heavily on the contaminants' nature, the substrate, environmental conditions, and concentration. The presence of UV radiation likely modifies the formation of droplets, films, or clusters, thereby impacting the performance of onboard instruments.

Thanks to recent advances in the molecular characterization of degassed or re-emitted species, it is now possible to revisit this subject and refine and confirm these mechanisms. This thesis aims to identify the species (or classes of species) sensitive to these phenomena and the reaction intermediates (radicals) and specify the mechanisms involved. To accomplish this, a test protocol must be defined and validated to determine the parameters of the confirmed models for each material and species.

The main activities will consist of:

1. Characterizing the incoming flux and reaction intermediates at the chemical species level. One method is to desorb metastable species by reheating.

2. Define and validate a test protocol to identify reactions and reaction intermediates applicable to future routine testing.

Thus, this thesis will contribute to a better understanding of UV-contaminant interactions in space, which has implications for material durability and contamination management in orbit.

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For more Information about the topics and the co-financial partner (found by the lab!); contact Directeur de thèse - Jean-Francois.Roussel@onera.fr

Then, prepare a resume, a recent transcript and a reference letter from your M2 supervisor/ engineering school director and you will be ready to apply online before March 13th, 2026 Midnight Paris time!