Characterization of Multiple Layer Alloys

One of the most common methods for characterizing nanometer-wavelength multiple-layer alloys is x-ray diffraction (XRD), which provides information about the crystalline texture and superlattice structure of a multiple-layer material. The superlattice structure of the alloy is revealed as satellite peaks located at low and high angles around the crystallographic Bragg peaks in the diffraction pattern. The dispersion angle of the satellite peaks provides the modulation wavelength of the multiple layer, and the number and amplitude of the satellite peaks provide a measure of the interfacial "sharpness" between each lamella. The wavelength of a multiple-layer alloy (X) is quantitatively related to the first-order satellite peak locations through the relationship l = -

where Xx is the x-ray source wavelength, 9+ is the high-angle satellite peak location, and 9" is the low-angle satellite peak location. Transmission electron microscopy and Auger electron spectroscopy (used with sputtering) have both been employed to study nanometer-scale structure in multiple-layer alloys, but these techniques require significantly more sample preparation and handling than XRD. Moreover, the sample preparation for these techniques requires destructive treatment of the multiple-layer material.

Once the structural characteristics of a multiple-layer alloy are known, then the material properties are normally analyzed using conventional techniques. Relationships have been observed between the superlattice structure of multiple-layer alloys and their mechanical properties (e.g., tensile strength, moduli), their electrical properties (e.g., conductivity), their magnetic properties (e.g., magnetoresistance, magnetostriction, saturation magnetization), and their chemical properties (e.g., corrosion resistance).

The growing technological need for inexpensive, high-performance thin-film materials is propelling academic and industrial research efforts to understand the processing-structure-property relationships in a wider range of plated multiple-layer alloys. The degree to which plated multiple-layer films will ultimately meet the technological challenges that face surface engineers remains to be answered.

Selective (Brush) Plating

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