PNNL

Abstract

Thin film superlattice materials can exhibit physical, optical and mechanical properties very different and superior to those of single layer counterparts. In the past fifteen years, hard coating, optical and electrical device technologies have advanced beyond the use of single layer coatings with the development of nanoscale compositionally modulated coatings, or superlattices and nanocomposites. A typical superlattice consists of hundreds to thousands of nm-scale layers with alternating compositions and/or crystalline phases. It is possible to engineer the electrical and mechanical properties by choice of layer thicknesses and compositions. Typical layer thicknesses are between 2 and 100 nm. We report of three types of superlattice coatings: (1) AlN/Si3N4 optical superlattice for abrasion protection of ZnS IR windows, (2) Al/Cu structural superlattices and (3) advanced thermoelectric superlattices. All superlattice coatings were deposited by DC and RF reactive magnetron sputtering. The AlN/Si3N4 superlattice had layer thicknesses of 2 nm and exhibited a nanohardness of 35 GPa. The Al/Cu superlattice had layer thicknesses of 1.5 nm and a hardness near 6.5 GPa and is being developed for lightweight optics for space applications. The thermoelectric superlattice demonstrated a figure of merit (ZT) ~ 1.5 and is being developed for power generation from waste heat sources.