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Title: Phase formation in codeposited alloy thin films
Author: Saunders, N.
ISNI:       0000 0001 3553 9901
Awarding Body: University of Surrey
Current Institution: University of Surrey
Date of Award: 1984
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Alloy thin films of Cu-Ag, Pd-Rh and Cu-Sn have been codeposited over a range of substrate temperatures by secondary ion beam sputter deposition and examined using x-ray diffraction, Transmission and Scanning Electron Microscopy. Depending on the substrate temperature either equilibrium or metastable phases are formed. It is postulated that the formation of multi-phase structures in codeposited alloy films is controlled by the diffusional breakdown of fully intermixed depositing atoms, so that three kinetic regimes are observed as the substrate temperature is varied: (1) At low T/T[m] the surface mobility is insufficient for the decomposition of the fully intermixed depositing atoms and the films contain metastable single phase structures. (2) With increasing substrate temperature decomposition to metastable two phase structures is observed. (3) Finally with a further increase in substrate temperature the atomic mobility at the surface is sufficient to allow the full atomic rearrangements necessary for the formation of equilibrium phases. By relating the distance an atom can move on the surface during deposition to substrate temperature and deposition rate, it has proved possible to accurately predict the substrate temperature for the metastable two phase → equlibrium transition in all the alloys studied, and hence the conditions for the deposition of films containing equilbrium phases. The metastable phases found in the Cu-Ag and Pd-Rh films are simply formed by the supersaturation of the equilibrium f.c.c. phases. However, the Cu-Sn alloy films exhibited a complex deposition behaviour at low T/T[m] substrate temperatures, with the formation of two phases that are not observed in the phase diagram, and the formation of the zeta phase, found only at high temperatures and within a narrow composition range in the equilibrium phase diagram. An hypothesis is put forward that relates the metastable phases formed in the first kinetic regime to Free Energy vs composition diagrams at the temperature of the substrate. This gives excellent correlation with the metastable phases that are formed both in the Cu-Sn alloy films and in codeposited alloys previously reported in the literature.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Solid-state physics