Effect of oxygen concentration on the chemical behavior of deuterium implanted into oxygen-containing boron thin films

Boronization is planned as one of the wall conditioning techniques for impurity reduction in fusion plasmas. Oxygen-containing boron films were prepared for simulating boronization, and exposed to energetic deuterium ions. From the XPS results, it was found that the B-1s peak energy was shifted to higher energy as the oxygen concentration increased. However, the deuterium retention decreased according to TDS. In addition, deuterium desorption was observed at a higher temperature, which is not found for a deuterium ion implanted pure boron film. These facts indicate that boron oxide was formed and deuterium was trapped by forming O–D bond when the oxygen concentration was above 37%. We conclude that the oxygen concentration should be kept less than 10% to prevent high tritium retention on the surface of the first wall in the future fusion devices.