Our research focus is the synthesis of thin films by surface-controlled reaction to afford ultra-smooth, conformal, superconformal, or nanostructured surfaces for use in electronic, photonic, magnetic or tribological applications.
The primary experimental approach is low-temperature chemical vapor deposition (CVD) under conditions where molecular adsorption is strong and the reaction (film growth) rate is moderated by surface site blocking or associative desorption processes. An innovation in our work is the use of neutral ‘inhibitor’ molecules to control the surface kinetics.
Our work involves a very close collaboration with the group of Prof. Greg Girolami in the Department of Chemistry. They specialize in the invention and synthesis of new precursor molecules for the CVD process. These molecules are designed to react at desired substrate temperatures to afford high purity materials. However, if a molecule is not satisfactory, the group of Prof. Girolami creates a new variant for us by modifying the ligand groups. Thus, our joint group effort operates at the leading edge of invention and new possibilities in thin film growth.
Current systems under study include: refractory and ultra-hard metal diborides; oxides of Ti, Mg, and the rare earths; copper and silver; iron, cobalt and other magnetic materials.
We have invented a method to grow films in a superconformal fashion, in which the thickness increases with depth below the opening of a deep feature. This will enable the complete filling of such features, as required in microelectronic and nanoscale device fabrication. Figure: cross-sectional SEM image of superconformal filling of deep trenches with CrB2.
We have invented a method to control the density and size distribution of nuclei on relatively unreactive substrates. This can be used to deposit ultra-smooth, ultra-thin films, or instead, an array of relatively uniform islands for plasmonic applications. Figure: AFM image of HfB2 islands on SiO2 substrates, where the island size distribution has been purposefully controlled.
Kinetic and atomic mechanisms are determined in-situ using spectroscopic ellipsometry, desorption mass spectroscopy and reflection IR absorption. Ex-situ analyses include coverage profiles vs. depth in deep substrate features as well as the suite of methods in the Center for Microanalysis of Materials at UI.