Organometallic compounds provide volatile sources of metals used for the deposition of insulating, semiconducting and metallic films. Our projects focus on deposition of transparent conducting oxides using organometallics in combination with ozone, atomic oxygen or molecular oxygen. The resulting films become part photovoltaic or other devices for which electrical conductivity, optical transparency and electronic structure of the films are critical to the device function. One of our primary goals in this research is to learn how the deposition chemistry impacts the composition and structure of the resulting film.
Atomic Layer Deposition in Tandem Solar Cells
As part of our collaboration with the Campbell group in the Department of Electrical and Computer Engineering and the Aydil group in Department of Chemical Engineering and Materials Science we are developing atomic layer deposition (ALD) processes to deposit transparent conducting oxide layers at the junction between absorbing layers in a tandem solar cell. Atomic Layer Deposition (ALD), the controlled layer-by-layer growth of thin films is often the method of choice to prepare thin films of uniform thickness over large areas, especially on surfaces with complex topography.
Atomic Layer Deposition on Porous Polymer Templates
When the components of block polymers undergo phase separation the resulting self-assembled microstructures can be used as templates for a variety of applications such a bit-patterned magnetic media for data storage. In collaboration with the Hillmyer group in the Department of Chemistry and the Leighton group in the Department of Chemical Engineering and Materials Science, we are using ALD to modify the size of pores of the initial template and to convert it into an inorganic material that can withstand higher temperature conditions.
Precursors for Hybrid Molecular Beam Epitaxy of Metal Oxide Films
Molecular beam epitaxy (MBE) is used to prepare single crystal, epitaxial films of the highest quality, which are critical for the exploration of their fundamental properties. For complex oxides such as BaSnO3, achieving ideal stoichiometry can be difficult using traditional metal sources. Hybrid MBE incorporates organometallic precursors into the process as a source of one of the metals, which means that chemistry will play a role in the deposition. In collaboration with the Jalan group in the Department of Chemical Engineering and Materials Science, we are exploring this chemistry by making systematic changes in the molecular structure of the precursor and determining the impact these changes exert on film composition, structure and properties. Our initial work focuses on organotin precursors used in the deposition of SnO2, BaSnO3 and related complex oxides.
Probing Chemical Reactions Used in Deposition Processes
Computational methods provide a critical means of unraveling the complex reaction mechanisms involved in the deposition of films. This is especially important for elucidating chemistry occurring at elevated temperatures that are difficult to probe experimentally. In collaboration with the Cramer group in the Department of Chemistry, we are using density functional and other methods to identify possible reaction pathways and have identified fascinating reactions between surface-bound metal alkyls and ozone. This is just one of the reactions used in ALD to deposit metal oxide films.