Tetragonal states of palladium II. Experiment

The goal of this work is to try and stabilize by constrained pseudomorphic epitaxy the body-centered-tetragonal (bct) phase of Pd that was revealed by the epitaxial Bain path (EBP) at the axial ratio c/asimilar to0.9. The substrate chosen is W{001}, and Pd is deposited on it in ultrahigh vacuum at room temperature. The films obtained are pseudomorphic with the substrate, but quantitative low-energy-electron diffraction (QLEED) analysis suggests that they do not consist of pure Pd. The analysis provides strong evidence for the fact that Pd and W interdiffuse, producing an alloy of Pd and W. In order to avoid alloy formation, and yet maintain conditions for pseudomorphism, a diffusion barrier is introduced in the form of a pseudomorphic film of Mn on W{001}. A Pd film with thickness of about 19 Angstrom is then grown pseudomorphically on top of the Mn film and analyzed by QLEED. The film is highly strained and defective, allowing only mediocre agreement between theory and experiment, but the analysis shows that its structure is probably a strained state of the bct phase found on the EBP.