The Control of Interfacial Reactions Via Length Scales of Ultrathin-Film Modulated Composites

Autor: Thomas Novet, David W. Johnson, Christopher A. Grant, Loreli Fister, John McConnell
Rok vydání: 1991
Předmět:
Zdroj: MRS Proceedings. 238
ISSN: 1946-4274
0272-9172
DOI: 10.1557/proc-238-629
Popis: Interfaces are difficult to probe because the volume of the interfacial region is exceedingly small compared with the bulk. Our approach is sequentially to deposit thin (5–50Å) elemental layers to create a unique initial reactant. Due to the short modulation length, the interfaces constitute a large fraction of the total composite. Composites modulated below a critical repeat unit length are found to evolve into homogeneous amorphous alloys. Composites modulated above this critical distance behave like bulk diffusion couples. The layered nature of the starting reactant permits the evolution of the interfacial structure to be followed in a quantitative manner using x-ray diffraction. Distinct differences in the evolution of the interfaces above and below the critical distance are observed. This approach to studying interfaces also permits the direct and selective synthesis of crystalline compounds. Nucleation is the rate-limiting step in the formation of a crystalline material from an amorphous alloy, and the phase formed is strongly influenced by the stoichiometry of the homogeneous amorphous alloy. Results from studies of molybdenum-selenium and iron-silicon ultrathin-film composites will be discussed.
Databáze: OpenAIRE
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