Fabrication and Properties of Nanolaminates

Nanocomposites are a new frontier in materials science because composites can have very different properties than their constituents. We are focusing on nanolaminate composite materials. Nanolaminates show unique physical properties when the nanolayer thickness is less than the characteristic length scale that defines the physical property. For example, thermal conductivity is reduced when the nanolayer thickness is less than the mean free path of the phonon that transfers the heat. Likewise, hardness is increased when the nanolayer thickness is less than the dislocation length for the slip plane motion that characterizes the response of the material to stress.

Our nanolaminate work has recently focused on Al₂O₃/ZnO [1,2] and Al₂O₃/ W nanolaminates. These are interesting nanolaminates for a variety of reasons. Electrically, Al₂O₃ is an insulator and ZnO and W are both conductors. Structurally, Al₂O₃ is amorphous and ZnO and W are both nanocrystalline. By depositing these nanolaminates with various compositional ratios and different nanolayer thicknesses, the electrical and structural properties of the film can be tuned over a wide range.

The Al₂O₃/W nanolaminate may also be useful as a high temperature thermal barrier coating to protect turbine engine blades. The Al₂O₃/W nanolaminates may also be very useful as x-ray Bragg mirrors in the hard x-ray region. A cross-sectional transmission electron micrograph (TEM) of one of the Al₂O₃/W nanolaminates is shown in the accompanying figure.

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