Nanostructured Composite Coatings: Growth and Applications

A.U. Mane, J.W. Elam
Argonne National Laboratory,
United States

Keywords: nanocomposite, ALD, metal fluoride, CSP, MEMS, MCP, Li-ion Battery

Summary:

We have an developed atomic layer deposition (ALD) method to synthesize nanocomposite coatings comprised of metallic nanoparticles embedded in an amorphous dielectric matrix. These films have numerous applications including medical imaging, homeland security, microelectronics and energy storage. These ALD coatings are nominally composed of M:Al2O3 where M= W, Mo or Ta. By varying the ratio of ALD cycles for the metal and the Al2O3 components in the film, we can precisely tune the composition and structure of these coatings over a very broad range. These films exhibit tunable Ohmic behavior and resist breakdown even at high electric fields of 1E7 V/m as well. In addition, the coatings are chemically and thermally robust. Moreover, the self-limiting nature of ALD allows us to grow these films over large areas, inside of high aspect ratio substrates, and on complex 3D surfaces. To investigate the ALD growth mechanism for the nanostructure composite films we employed in-situ quartz crystal microbalance (QCM), quadrupole mass spectrometry, and Fourier transform infrared (FTIR) absorption spectroscopy studies. For M:Al2O3 films, QCM showed that the metal ALD inhibits the Al2O3 ALD and vice versa. Despite this inhibition, the relationship between metal content and metal ALD cycle percentage was close to expectations. Depth profiling X-ray photoelectron spectroscopy showed that the M:Al2O3 films are uniform in composition across the thickness of the layer. Cross-sectional transmission electron microscopy (XTEM) revealed the film microstructure to be metallic nanoparticles (~1-2 nm) embedded in an amorphous matrix. The transport properties of these M:Al2O3 were studied as function of ratio of metal to Al2O3 ALD cycles. We have utilized these nanocomposite coatings to functionalize capillary glass array plates to fabricate large-area microchannel plates, charge drain coatings in microelectromechanical system (MEMS) devices, protective coatings on Li-ion battery electrodes, and selective solar absorber coating for concentrated solar power.. Here we will discuss the ALD growth, characterization, and applications of these ALD nanostructure composite coatings.