Implantation and Diffusion of Cu in Be

Abstract

The implantation and diffusion of Cu in single-crystal Be has been studied. Backscattering of 2 MeV He⁺ ions was used to determine the concentration-versus-depth profile to ≈ 2 µm with a resolution of ≈ 300 Å. Room temperature implantations were made 8° from the C and A crystalline axes respectively, at 100 keV incident energy. Implantation fluences of 4–5 × 10¹⁶ Cu/cm² were used throughout, except for one lower fluence ≈ 7 × 10¹⁵/cm². The position (900 ± 100) Å and width (850 ± 100) Å of the peak in the Cu profile agree fairly well with the LSS theory. An extended tail at greater depths also was present, however, suggesting enhanced diffusion during the room temperature implantation. Isochronal anneals between 400 and 650° C showed a strongly temperature-dependent diffusion rate above approximately 550° C, with a much weaker temperature dependence below 550° C. The existence of such a low temperature region is again suggestive of damage-enhanced diffusion. A series of isothermal anneals at 595° C demonstrated that the penetration depth is proportional to the square root of the total anneal time, as expected from the diffusion equation, and showed no evidence of Cu being trapped near the surface. The diffusion constants D_C and D_Afor the C and A axes, respectively, are different, with D_C/D_A = 0.6 ± 0.1 at 595° C. Published data for autodiffusion in Be give D_C/D_A = 0.4 at 595° C, whereas from the model of LeClaire this ratio is expected to be larger for autodiffusion than for Group IB metals in Be. An even larger inconsistency has previously been reported for diffusion of Ag in Be for which D_C/D_A= 2.3 at 595° C.

This work was supported by the U.S Atomic Energy Commission.