A direct observation of the trapping of deuterium ions at a grain boundary in tungsten

Abstract

The imaging atom-probe/field ion microscope has been used to study the trapping of low-energy deuterium ions in tungsten. The experimental results indicate that implanted deuterium does not remain trapped in a tungsten lattice at room temperature for a period of several days unless a defect is present. Time-gated imaging atom-probe images show the first direct correlation between the trapped deuterium and the presence of a grain boundary on an atomic scale. Comparing these results to secondary-ion mass spectrometer and nuclear reaction analyses of simultaneously exposed, flat tungsten, and silicon samples indicates that the imaging atom-probe is sensitive to low levels of hydrogen concentration at lattice defects that are invisible to these other two techniques. The implications of the experiment relating to tokamak plasma-wall and hydrogen embrittlement studies are discussed.