Trapping and Detrapping Mechanisms of Deuterium in SiC Studied by XPS and TDS Techniques

Abstract

The elucidation of the trapping and detrapping mechanisms of hydrogen isotopes in SiC is one of the most critical issues for future fusion reactors if SiC is used as the first wall and structure material. In this study, 1 keV deuterium (D 2 þ ) ions were implanted into SiC and the chemical states of C and Si were evaluated by X-ray photoelectron spectroscopy (XPS). The deuterium desorption and retention were also analyzed by thermal desorption spectroscopy (TDS). The deuterium desorption behavior for SiC was compared to that for Si and graphite, and it was found that deuterium is preferentially trapped by C and, after the saturation of the C-D bond, it is trapped by Si in SiC. Deuterium desorption was found to consist of two stages, namely deuterium desorptions bound to Si and C. Their trapping mechanisms were influenced by the damaged structures produced by the D 2 þ ion implantation. Finally, deuterium retention in SiC at temperatures above 700 K was higher than that in graphite, indicating that tritium retention in SiC may be high compared to that in graphite during plasma operation.

Deuterium retention in SiC coated graphite by D2+ implantation

“…Comparison with the deuterium retention behavior in polycrystalline ␤-SiC reported in [5,7], two similar points were observed. For polycrystalline ␤-SiC, there are also two desorption peaks in TDS spectra and deuterium was also trapped preferentially by C in the initial implantation.…”

“…It was reported that implanted hydrogen will be trapped by two vacancies in SiC, namely the carbon vacancy and silicon vacancy. If both types of vacancy are present, implanted hydrogen is preferentially trapped by silicon vacancy [7,8]. Therefore, for the trapping process of hydrogen isotopes, it was found that D was preferentially trapped by C in the initial D 2 + implantation.…”

Dependence of implantation temperature on chemical behavior of energetic deuterium implanted into tungsten carbide

“…6, in which the D retention in pyrolytic graphite (D/C) and SiC (D/ SiC · 0.5) are also shown [10,11]. The D retention in WC was decreased significantly up to 573 K, and the reduction became almost gradual above 573 K, where the amount of D bound to C was less than 20% of the D retention at 323 K. It should be noted that the D retention in WC was much less than those in the other materials, one fifth of that in pyrolytic graphite and one sixth in SiC.…”

Overview of research and development activities on fusion nuclear technologies in Japan

“…Tritium transfer behavior through concrete material is studied at Kyushu University [38] and the diffusivity of water was expressed using the obtained adsorption isotherm. The hydrogen isotope behavior in typical plasma facing materials, namely graphite, SiC, WC and boron, were studied at Shizuoka University and The University of Tokyo, and the correlation between chemical state of materials and hydrogen isotope desorption process was discussed [39,40].…”