Geometric factors in f.c.c. and b.c.c. metal-on-metal epitaxy. Part I. Deposits of Cu and Ni on (001) Ag

Abstract

Electron microscopy has been used to examine films of Cu and Ni (mean thickness, t _m ⩽ 100nm) vacuum-deposited (1 × 10⁻⁷−5 × 10⁻⁴ N m⁻²) at substrate temperatures, T _S, in the range 93 K-700 K onto (001) Ag films.

The results show that under certain conditions it is possible to prepare a metal deposit with a crystal and/or defect structure not usually observed for this metal. Thus Ni films were a mixture of f.c.c. and h.c.p. material at T _S < 525 K and Cu films were b.c.c. if t _m< 10 nm at T _S ≈ 300 K. Films of b.c.c. Cu were (001) epi-taxed, i.e. (001) Cu ‖ (001) Ag with, say, [110] Cu ‖ [100] Ag. Continuous films of f.c.c. Cu were (001) epitaxed single crystals at T _S > 600 K, i.e. they were oriented (001) Cu ‖ (001) Ag with, say, [110] Cu ‖ [110] Ag. At T _S ≈ 600 K the films also contained a few (110) epitaxed grains. The latter were oriented (110) Cu ‖ (001) Ag and occurred in two domains aligned with, say, [111] Cu parallel to either [100] Ag or [010] Ag. The (110) grains contained high concentrations of thin twins exclusively parallel to (111) Cu. At T _S ≈ 300 K, continuous films of f.o.c. Cu consisted of about equal proportions of (001) and (110) epitaxed grains.

Films of Ni epitaxed (001) at T _S > 525 K. At T _S ≈ 300 K they consisted of similar proportions of (001) and (110) epitaxed grains and at T _S ≈ 93 K only of (110) grains. In Ni films the two (110) domains were characterized by high concentrations of stacking faults (rather than twins) exclusively parallel to (111) Ni. The faulting caused appreciable parts of Ni (110) grains to adopt the h.c.p. structure.

A tentative model is proposed to account for the change in epitaxy and crystal structure with T_S.