Highlights

• Precipitation of implanted He is a major concern for the performance and survivability of plasma-facing components in future fusion reactors.
• In the Applied Physics Letters 98, 241913 (2011) *, the use of NR is reported to study the Cu/Nb layered nanocomposites resistive to high He doses.

(left) NR data (filled black circles) from [Cu/Nb]x samples and fitting curves (red solid lines). (right) SLD profiles obtained from the NR fits and schematics of the real-space interpretations. A prime indicates that the curve corresponds to a measurement after He ion implantation.

*Selected as a frontier research by the American Institute of Physics and the American Physical Society.

Neutron Reflectometry Helps To Understand the Performance of Radiation-Resistant Materials

Precipitation of implanted helium is a major concern for the performance and survivability of plasma-facing components in future fusion reactors. The deleterious effects of He may be minimized if it can be trapped at special microstructural features, such as YTiO clusters in oxide dispersion strengthened steels. Recent work on metallic multilayers indicates that a remarkably high concentration of He can also be trapped at certain heterophase interfaces before nanometer-scale bubbles are resolved via transmission electron microscopy (TEM). Atomistic modeling suggests that excess atomic volume leads to a high He ‘solubility’ at these interfaces. Since TEM cannot resolve He clusters smaller than 1-2 nm in diameter, there is a need to characterize He concentration profiles across interfaces via other techniques. The ideal technique would be directly sensitive to He, and additionally, have markedly higher depth resolution than ion-beam analysis techniques such as elastic recoil detection (ERD) or nuclear reaction analysis (NRA). In the paper “Trapping of implanted He at Cu/Nb interfaces measured by neutron reflectometry” published in Applied Physics Letters an interdisciplinary group of scientists report on the use of neutron reflectometry (NR) to quantitatively determine the changes in the transverse chemical profile of Cu/Nb layered nanocomposites due to He ion migration, absorption, and storage after ion implantation. NR experiments were performed on the reflectometer (SPEAR) at the Los Alamos Neutron Science Center. NR involves the specular reflection of a neutron beam from a surface or film and provide sub-angstrom level resolution in location of the He-enriched interfaces. From NR measurements, layer parameters such as thickness, density, chemical composition, and interface and surface roughnesses can be determined with high precision regardless of the crystallinity of the sample (single crystal, polycrystalline, or amorphous). Neutron scattering is a unique tool to study such nanolayered composites because the scattering strength is a non-monotonic function of the Z number of a material. Therefore, elements like Cu and Nb provide the necessary neutron scattering contrast even though their X-ray scattering contrast is low. Additionally, unlike electron microscopy which yields local structure information, NR provides data averaged over a large sample area.

“Trapping of implanted He at Cu/Nb interfaces measured by neutron reflectometry”, Mikhail Zhernenkov, Michael S. Jablin, Amit Misra, Michael Nastasi, Yongqiang Wang, Michael J. Demkowicz, Jon K. Baldwin, Jaroslaw Majewski, Applied Physics Letters, 98, 241913 (2011). (Selected as a frontier research for the June 27, 2011 issue of Virtual Journal of Nanoscale Science & Technology by the American Institute of Physics and the American Physical Society).

¹ Lujan Neutron Scattering Center, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
² Center for Integrated Nanotechnologies, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
³ MST-8, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
⁴ Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA