SURFACE CHEMISTRY AND DEPTH-RESOLVED CHARACTERIZATION OF MATERIALS FOR HIGH-ENERGY PHYSICS DETECTORS

The long-term reliability of modern particle detectors depends critically on the chemical and structural stability of the materials exposed to intense radiation fields and plasma environments. Understanding the microscopic mechanisms governing surface evolution is therefore essential for improving detector performance and lifetime. Recent investigations have demonstrated that the aging of gaseous detector materials involves complex physicochemical transformations, including the redeposition of polymeric fragments and elemental migration within metallic electrodes [1]. More recently, the interaction between CO₂-based gas mixtures and copper electrodes has been shown to promote controlled oxidation-state evolution and the formation of thin oxygenated surface layers, providing new insight into the remarkable long-term stability of these detector materials [2].

In this contribution, we present a unified view of these degradation mechanisms through the combination of complementary surface-sensitive and depth-resolved characterization techniques. Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) reveals the redeposition of polyimide fragments inside detector microstructures together with chromium migration from buried metallic layers, while Near-Ambient Pressure X-ray Photoelectron Spectroscopy (NAP-XPS) identifies the evolution of copper oxidation states and the formation of carbonyl, hydroxyl and carbonate species under controlled CO₂ atmospheres. Raman microscopy further confirms the heterogeneous distribution of Cu₂O and CuO phases, providing structural support for the oxidation-state evolution inferred from XPS.

The combined results demonstrate that plasma-induced degradation arises from the interplay between polymer fragmentation, elemental migration, gas–surface reactions and oxidation processes occurring within the first nanometers of the material. This multimodal approach establishes a comprehensive framework for understanding surface evolution in copper–polymer systems operating under harsh radiation environments and illustrates how complementary surface and depth-resolved analytical techniques can reveal degradation mechanisms that remain inaccessible to individual characterization methods.

References

[1] T. B. Saramela et al., “Evidence for polyimide redeposition and possible correlation with sparks in Gas Electron Multipliers working in CF 4 mixtures”, Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, v. 1066, p. 169573, set. 2024, doi: 10.1016/j.nima.2024.169573.

[2] T. F. Silva et al., “Surface mechanisms governing long-term stability of GEM detectors in CO2-based gaseous mixtures”, Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, v. 1090, p. 171638, out. 2026, doi: 10.1016/j.nima.2026.171638.