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He ion irradiation damage in multilayers
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View: Figures


Image of FIG. 1.
FIG. 1.

XTEM micrographs of as-deposited (a) multilayer films with KS orientation relationship between bcc Nb and fcc Al grains, and (b) multilayers with an average columnar grain size of less than .

Image of FIG. 2.
FIG. 2.

A SRIM calculation simulates the variation of He concentration vs radiation depth for He ions of and fluence of , same as the experimental condition, in multilayers.

Image of FIG. 3.
FIG. 3.

XRD patterns of (a) multilayers and (c) multilayers before and after He ion irradiations. Radiation induces a reduction in peak intensity and slight left shift of peak positions of Al (111) or Nb (110) diffraction. (b) Deconvolution of XRD peaks of irradiated specimen shows the formation of (210).

Image of FIG. 4.
FIG. 4.

XTEM image of after radiation. (a) At below the surface, few He bubbles can be seen primarily in Al layer. (b) In the peak damage region, from surface, a large number of He bubbles are observed. (c) At a depth of , essentially no damage is observed.

Image of FIG. 5.
FIG. 5.

Variations of Al (111)/Nb (110) lattice spacing in irradiated Al/Nb 100nm film, along implantation path, examined by SAD in XTEM studies with an aperture of in diameter. Superimposed is the SRIM calculation of He concentration profile. A minimum lattice spacing is observed at the peak He concentration region, corresponding to the lattice spacing of (210).

Image of FIG. 6.
FIG. 6.

Underfocused XTEM images of irradiated multilayer show the retention of layer interface at (a) surface, (b) peak damage, and (c) unirradiated regions. He bubbles are observed primarily in the peak damage regions. HRTEM micrographs of the corresponding regions shows rough interfaces in the surface and peak damage regions , and crystallographically well-defined interface in the unirradiated region .

Image of FIG. 7.
FIG. 7.

Chemical analysis of layer interface in irradiated multilayers. (a) STEM image reveals chemically abrupt interface close to surface, and wavy interfaces in peak damage region. (b) and (c) EDX composition profiles along lines and in Fig. 7(a) normal to the layer interfaces show the interface widths of and respectively by using a cutoff criterion of 10%–90%.

Image of FIG. 8.
FIG. 8.

STEM micrographs of irradiated multilayers at different depth. (a) surface, (b) peak damage region, and (c) unirradiated region. The corresponding EDX analyses along line markers show alternating Al and Nb compositions in and , and intermixing along interface in the peak damage region .

Image of FIG. 9.
FIG. 9.

(a) Comparisons of hardness vs for as-deposited (solid squares) and ion-irradiated (solid circles) multilayer films. The hardnesses of multilayers with layer thickness of greater than are fitted by using solid lines. (b) Hardness enhancement vs shows that the hardness increases slightly when is , whereas radiation hardening is significant and increases monotonically at smaller . Two horizontal dash lines indicate radiation hardening of single layer Al and Nb films subjected to identical radiation conditions. Two solid lines show calculated radiation hardening by considering defects, and using a simple model based on the formation of 0.5 and thick intermetallic layer along interface.

Image of FIG. 10.
FIG. 10.

Schematics of a composite model that consists of a thick layer along the layer interfaces in irradiated multilayers. The volume fraction of the intermetallic layer increases in multilayers of smaller .


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: He ion irradiation damage in Al∕Nb multilayers