Highlights

Atomic Layer Deposition Synthesis of Nanostructured Materials

Scientific Achievement

Atomic layer deposition (ALD) is a thin film coating technology allowing nearly any material to be deposited onto flat surfaces as well as complex, nanoporous substrates such as membranes and powders.  ALD uses gaseous precursors and self-limiting surface chemistry to deposit materials in an atomic layer-by-layer fashion.  We are currently pursuing a variety of applications for ALD technology including catalysis, photovoltaics, sensors, and solid state lighting.

Through our work at the EMC, we have made significant progress in the last year on several applications for ALD.  In particular, we have developed an ALD method for depositing materials at specific depth locations within nanoporous solids.  We call this technique “stripe coating”, and it has applications for synthesizing nanostructured catalysts to promote sequential chemical reactions (i.e. A?B?C).  As part of this work, we analyzed cross-sectional specimens of anodic aluminum oxide (AAO) membranes using EDAX measurements.  These measurements allowed us to determine the location of the stripes within the nanopores (see highlight viewgraph).  We found that we could precisely control the depth location and width of the stripes by adjusting the timing of the ALD exposures, and we were able to model this process using Monte Carlo simulations.

In a different project we have developed ALD methods for synthesizing high surface area electrodes for dye-sensitized solar cells (DSSCs).  The electrodes were prepared using AAO membrane templates by first depositing a conformal indium tin oxide (ITO) layer followed by a TiO₂ layer.  Cross-sectional SEM and EDAX measurements performed at the EMC (see highlight viewgraph) allowed us to verify the thickness and conformality of these coatings.  By fabricating and testing DSSCs using these electrodes, we discovered that the underlying ITO layer dramatically improves the solar cell efficiency by facilitating radial charge collection of the photo-generated electrons from the TiO₂ layer.

Significance

The techniques developed in this project have broad reaching implications, and we are beginning to apply our ALD technology to other fields including fuel cells, sensors, and solid state lighting.  Our mission is to develop and commercialize ALD thin film technologies, and we are pioneering the use of ALD methods to solve a wide variety of problems that challenge our nation’s current and future energy needs.  Our ALD research benefits enormously from access to Argonne’s Electron Microscopy Center.

Performers

J. W. Elam, J. A. Libera (Argonne-ES); A. V. Zinovev (Argonne-MSD)