Speaker
Description
E. Mitsi1,2, P.Tsavalas2, S. Pantousa2, M. Axiotis2, A. Lagoyannis 2, K. Mergia2, G. Apostolopoulos2
1 Department of Physics, National Technical University of Athens, Athens, Greece
2 National Centre for Scientific Research “Demokritos”, Agia Paraskevi, Greece
Presenting author email: elmitsi@ipta.demokritos.gr
Accelerator-based ion irradiation is widely employed to investigate radiation effects in solids. In fusion materials research, it is particularly valuable as a surrogate approach for studying neu-tron-induced damage. For ion irradiation to serve as a reliable tool for radiation damage studies, extrinsic effects such as impurity incorporation during the irradiation process must be mini-mized.
Ion beam-induced carbon uptake is a notable concern, particularly in studies of Fe-based ferrit-ic/martensitic steels, which are considered candidate structural materials for future fusion power plants. Carbon can influence microstructural evolution and irradiation response through its strong interaction with irradiation-induced point defects. Since the extent of carbon contamina-tion depends on the specific experimental conditions, it is important for ion irradiation studies on steels to verify whether carbon uptake has occurred and, where possible, to quantify it.
In the present study, carbon depth profiles of irradiated pure Fe films were acquired by combined Rutherford Backscattering Spectrometry (RBS) and Nuclear Reaction Analysis (NRA). The 50 nm Fe films were deposited by DC magnetron sputtering onto Si substrates capped with a 300 nm thermally grown SiO2 layer. The thickness and structure of the films were confirmed by X-ray reflectivity and grazing incidence X-ray diffraction. Specimens were irradiated with 4 MeV O²⁺ ions to a damage dose of 0.25 displacements per atom (dpa) and with 5 MeV Cu³⁺ ions to 1 dpa. The RBS/NRA measurements were performed using a 1.4 MeV deuterium beam and a surface barrier detector positioned at a scattering angle of 170o. Spectra were acquired from irradiated specimens, unirradiated reference samples, and the pristine Si/SiO2 substrate. All irradiations were conducted at the 5.5 MV Tandem accelerator of NCSR “Demokritos”. Carbon was detected via the 12C(d,p0)13C reaction. The carbon signal comprised a high-energy peak, attributed to a surface layer typically formed under high-vacuum conditions by hydrocarbon deposition, and a low-energy tail, associated with carbon distributed throughout the sample volume. Carbon profiles were quantified by simulating the RBS/NRA spectra with the SIMNRA code. For the given experimental conditions, the detection limit for the carbon volume concentration was ~ 2 · 1019 at./cm3. Carbon was identified in all specimens, exhibiting a characteristic near-surface enrichment and extending to a depth of approximately 4 μm. The irradiated specimens showed substantially higher carbon concentrations than the reference sample, consistent with ion-beam-induced carbon uptake. Quantitatively, the near-surface carbon concentration increased by 1.2(2) · 1020 at./cm3 and 2.4(2) · 1020 at./cm3 for the 0.25 dpa and 1 dpa specimens, respectively, demonstrating a dose-dependent enhancement of carbon incorporation.