A Study On Deuterium Retention In Carbon And Carbon-silicon Co-deposited Films Formed By RF Sputtering

The first wall materials have strict requirements because of the complex interaction between the first wall materials and D/T plasma in fusion device and one of these requirements is low D/T retention. Carbon material has unique performance, such as low Z, high melting point （4313 K）, high heat conductivity, small absorption cross section and good compatibility with plasma, so it is highly appropriate to be candidate materials. And SiC material has good heat conductivity, corrosion resistance, low density, and low induced radioactivity especially after irradiation etc, which make SiC crystals can be used in extreme conditions （ultra-high pressure, high temperature）. SiC material can be used as microelectronics and photoelectric aerospace materials, and the first wall materials in fusion device.In this article deuterium retention in carbon and carbon-silicon co-deposited films of the plasma facing materials in fusion experimental reactors has been studied. The C-D co-deposited layers were prepared on graphite and silicon substrates by using a graphite target （99.999% purity） in a RF magnetron sputtering system in pure deuterium （99.999% purity） discharge plasma for half hours. The C-Si-D co-deposited layers were prepared by using a graphite-silicon mixed target （C/Si=1/11） in a RF magnetron sputtering system in pure deuterium （99.999% purity） discharge plasma. The depth profiles of deuterium retention in the films were measured by means of elastic recoil detection analysis （ERD）. Film composition and thickness were determined by Rutherford backscattering spectrometry （RBS） analysis. The deuterium thermal desorption in the films was analyzed by thermal desorption spectroscopy （TDS）. The co-deposited deuterated SiC layers were investigated by infrared absorption spectroscopy （IR）, Raman scattering spectroscopy （RS） and scanning electron microscopy （SEM） observations.The C-D co-deposited layers thickness and D retention on C and Si substrates increased with the increasing D₂ gas pressure, but both of them decreased with substrate temperature increasing. The C-Si-D co-deposited layers thickness decreased with substrate temperature increasing but D retention is slowly increased. The C-Si-D co-deposited layers thickness and D retention increased with the increasing D₂ gas pressure. This is because Si content in the co-deposited layers increased with the increasing pressure and reducing substrate temperature, leading to C content rising. This result indicates that the temperature effect and high D₂ gas pressure on Si species is stronger than that on C species and the deuterium are mainly trapped by carbon atoms.Raman spectra of the C-Si-D co-deposition layers show Si nano-crystallites state （～520 cm-1） with the deuterated amorphous phase and a very weak peak of the second-order features of Si phonon mode （～970 cm-1） in low temperature. These imply that the deposition layer at 350K is dominated by mixture of the Si and C nano-particles containing crystallites as well as amorphous phases. As the deposition temperature increased, the ratio of D/G bands of carbon as well as Si peaks decreased greatly and the layers was to be more graphite-like.SEM images of the C-Si-D co-deposition layers deposited on Si substrate have been performed to investigate the surface of the layers. However, the further investigation is needed in order to figure out the characteristic of deuterium retention in other first wall materials.