A lithium depth-marker technique for rapid erosion and deposition measurements

作者：Sullivan R M^*; Pang A; Martinez Sanchez M; Whyte D G

来源：Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms , 2014, 319: 79-86.

DOI：10.1016/j.nimb.2013.10.024

• Nuclear reaction analysis
• Rutherford backscattering spectrometry
• Erosion
• Plasma facing surfaces
• Plasma materials interactions
• Depth profiling

A novel, high-resolution technique has been developed for the measurement of erosion and deposition in solid material surfaces. The technique uses a combination of nuclear reaction analysis (NRA) and Rutherford backscattering spectrometry (RBS) to determine the change in depth of a previously implanted marker layer consisting of Li-7. A scoping study shows that Li-7 is an ideal marker candidate due to a high Q (similar to 18 MeV) nuclear reaction, Li-7(p,alpha)He-4. Net erosion or deposition is measured by NRA of modified alpha energy passing through the bulk material. The reaction's high cross-section provides for the fast time resolution needed to measure erosion from high flux plasmas, and a highly penetrating proton beam provides for a large range of erosion/deposition measurements. Additionally, the implantation of low-Z Li leads to relatively low vacancy concentrations in the solid material due to implantation. This technique thus provides greater assurance that the measured erosion rate is indicative of the solid material: due to both the low vacancy production and the fact that no films or deposits are involved. Validation was performed by comparing the measured and predicted amount of erosion based on previously measured sputtering yields; the two were found to agree, within the uncertainty of the experiment. The depth resolution of the techniques is similar to 60 nm at a net erosion depth of about 1 mu m. The benefits of this technique are summarized as: short time scales (minutes) to obtain results, the marker layer can be used in any solid material, greater assurance that the measured erosion is indicative of the unperturbed solid material, and the continuous monitoring of the surface composition for contaminants and/or identification of deposited species using RBS simultaneous with the NRA.

• 单位
  MIT