Applied and Engineering Physics
After receiving his doctoral degree in physics from Rutgers, Dr. Fennie spent two years at The Center for Nanoscale Materials at Argonne National Laboratory as the Nicholas Metropolis Fellow. He joined the Cornell faculty in July of 2008 and works in the broad area of computational/theoretical materials physics including Materials-by-design.
Starting at the level of electrons and atoms, rationally design real materials heterostructures with targeted macroscopic properties conducive for electro- and photo-catalytic applications.
For example, the photocatalysis of water at oxide semiconductors (e.g. TiO2 ) to generate hydrogen and oxygen – one of the most promising approaches for harnessing solar energy – reveals the complexity of the problem. The challenge is to develop a highly efficient (>10%), stable, and cost-effective material capable of directly catalyzing the splitting of water to oxygen and hydrogen as existing materials are either too inefficient (1-2%) or too unstable. A number of properties need to be optimized in order to achieve the desired performance criteria. First, the quasiparticle gap (Eqp ) must be larger than 1.23eV in order to drive the uphill water splitting reaction (due to losses, this number is typically stated as Eqp>1.5eV). Second, the optical gap must be matched to the solar spectrum, i.e., in the visible Eop < ~2.5eV, in order to achieve high efficiency. Third, the subsequently created electron and hole pair must be separated and transported to the respective active surface before recombination takes place. Fourth, the chemical potential of these electrons and holes must be such that water is reduced and oxidized by the photogenerated electrons and holes, respectively, i.e., the relative position of the conduction (valance) band must be more negative (positive) than the reduction (oxidation) potential of water. An additional constraint is that the surfaces must also be designed to provide low energy pathways so as to minimize energetic losses.
Considering the multitude of properties required in a single material system, we seek a highly tunable and multifunctional class of materials that has the ability to be synthesized with atomic scale precision thereby facilitating the design of new materials with the desired properties built in. Complex oxides such as SrTiO3, which are one of the few classes of materials that can directly split water (albeit with low efficiently due to the large optical gap), are such materials. We will explore several unique strategies to tailor the electrical and optical properties of complex oxide materials:
- Strain engineering
- Interface Phases stabilized in artificially layered systems
- Narrow gab ferroelectrics