Palladium Substrate Research Articles

Imperfect Misfit Dislocations in Thin Films of Silver on Palladium

A calculation of the energy of complete and partial misfit dislocations has been made. This suggests that the misfit between an (001) silver film and a palladium substrate will be accommodated by partial misfit dislocations. The extrinsic stacking faults associated with these partials are expected to lie in the silver film and modify its crystal structure. To test these predictions silver films were grown in ultrahigh vacuum (2 × 10−9 Torr) on cold (−5 to −105 °C) palladium surfaces prepared inside the chamber. Transmission electron-diffraction patterns from these specimens showed that the silver films contained a high density of stacking faults.

Structural Influences on Adsorbate Binding Energy. I. Carbon Monoxide on (100) Palladium

The structural arrangement and binding energy of CO adsorbed on a (100) surface of palladium have been determined and related to each other over the submonolayer coverage range. There are four distinct equilibrium structural arrangements of CO: (1) At low coverages (< 0.4 monolayers) a random lattice gas configuration is observed in which each CO molecule is localized on a specific adsorption site. (2) Just below 0.5 monolayers a liquidlike short-range order arrangement is found. (3) At exactly 0.5 monolayers a c(4 × 2) − 45° overlayer structure forms which is in complete registry with the substrate. (4) For coverages greater than 0.5 monolayers, the c(4 × 2) − 45° structure is uniaxially compressed to form an overlayer which is out of registry with the palladium substrate. The observed linear decrease in binding energy with coverage up to 0.5 monolayers suggests that the only important CO–CO interaction occurs between nearest neighbors. Near 0.5 monolayers an almost discontinuous decrease in the binding energy of 0.35 eV is attributed to loss of registry between the overlayer and substrate. As the coverage increased above 0.6 monolayers the binding energy again decreased sharply as a consequence of neighboring CO orbital overlap.

Accommodation of misfit across the interface between single-crystal films of various face-centred cubic metals

Abstract Specimens consisting of a pair of single-crystal films in contact and in parallel orientation were prepared by successive evaporation of the film materials in ultra-high vacuum onto the (001) surfaces of hot sodium chloride crystals. The combinations of film materials used were gold-palladium, gold-silver and platinum-gold. Examination of the specimens by transmission electron microscopy revealed that the difference between the lattice parameters of the pairs of metals was divided between elastic strain and misfit dislocations in approximately the manner predicted by van der Merwe (1963). Most of the 4·6% misfit between a 100 A gold film and its 400 A palladium substrate was accommodated by misfit dislocations. The 0·19% misfit between a gold film and its 1500 A silver substrate was entirely taken up by elastic strain until the thickness of the gold reached between 250 A and 300 A. When the thickness of the gold film exceeded 250 to 300 A some misfit was accommodated by dislocations that moved by...