Effect of substrate temperature on microstructure and deuterium retention of molybdenum co-deposition with oxygen

The formation of co-deposition has a large impact on plasma surface interactions. It has been reported that co-deposition of Mo and O changed the surface properties of the TRIAM-1M tokamak and affected the confinement of the plasma. In this work, the influence of the substrate temperature on the crystallographic structure and hydrogen retention of the Mo-O co-deposition was studied by means of transmission electron microscopy and thermal desorption spectroscopy. Microstructures and hydrogen retention of the depositions showed a remarkable substrate temperature dependence. The deposition formed at high temperatures (>673 K) was found to be Fe₂MoO₄, which is the oxide of deposited elements and substrate elements. For the deposition formed and implanted at high temperatures (>573 K), the retention of deuterium is negligibly small. These results indicate that the retention of the hydrogen isotope is expected to become quite small by optimizing the wall temperature, even if the peculiar material is formed on the plasma-facing surface.