Geometric factors in f.c.c. and b.c.c. metal-on-metal epitaxy III. The alignments of (111) f.c.c.-(110) b.c.c. epitaxed metal pairs

Abstract

Deposits (≤ 100 nm thick) of Ni, Cu, Au and Ag condensed in u.h.v. onto (110) tungsten surfaces in the range 300-1200 K have been examined by transmission electron microscopy (TEM). In general agreement with the results of LEED, FEM and FIM on very thin deposits or individual small crystals, the metals epitax (111) f.c.c.// (110) b.c.c. in one of two types of alignments [110] f.c.c.// [001] b.c.c. (Ni and Cu) or [011] f.c.c.// [111] b.c.c. and [101] f.c.c.// [111] b.c.c. (Au and Ag).

All deposits of f.c.c. metals on (110) b.c.c. metal substrates and deposits of b.c.c. metals on (111) f.c.c. metal substrates examined so far epitax as above. The distribution of the alignments as a function of ρ = d₀ b.c.c./d₀ f.c.c., the ratio of the bulk atomic diameters of metal pairs, is analysed. Scaled nets of discs representing (111) f.c.c. and (110) b.c.c. planes are superimposed in the two types of alignments and the resulting patterns compared. Areas where discs in the two nets coincide are more elongated in the adopted alignment. This differentiation is used to predict the alignment of other f.c.c.-b.c.c. metal pairs in the range 0·82 < ρ < 1·15.

When W substrates deviate from (110), Ni and Cu also epitax (001) f.c.c.// (110) W with[1 10] f.c.c.//[111] W or [110] f.c.c.//[111] W; f.c.c. metals are expected to adopt this orientation also on (110) b.c.c. when ρ > 1·2.