Influence of tungsten-carbon mixed layer and irradiation defects on deuterium retention behavior in tungsten

The D₂⁺ fluence dependence on deuterium (D) retention was studied to clarify the D retention mechanism in tungsten. The additional D desorption stage was observed around 660 K in the TDS spectrum for a sample implanted with D₂⁺ up to the fluence of 10²³ D⁺ m^-2, which desorption stage was not observed the D ₂⁺ implanted sample with the fluence less than 10 ²² D⁺ m^-2. The TEM observation showed that the highly dense voids were formed in tungsten by D₂⁺ implantation with the fluence of 10²³ D⁺ m^-2, considering that the D would be trapped by voids. To understand the D trapping by voids in C⁺ implanted tungsten, C⁺-D₂ ⁺ sequential implantation experiments at various C⁺ implantation temperatures were performed. It was found that the amount of D desorbed around 560 K was increased by increasing the C⁺ implantation temperature. The formation of the voids was observed with increasing the C ⁺ implantation temperature by TEM, indicating that the increase of D desorption around 560 K was caused by the formation of voids. However, the desorption temperature of D trapped by voids in C⁺ implanted sample was lower than that in D₂⁺ implanted one. TEM observation and XPS measurement indicated that this difference was caused by the increase of void size and/or the presence of implanted carbon.