Research Overview

Transition metal nitrides (TMNs) offer stronger bonding covalency than oxides, leading to improved charge transport. Yet, semiconducting TMNs remain largely unexplored due to the difficulty of material synthesis. Using reactive sputter deposition, our group creates a growth environment rich in highly reactive nitrogen species, enabling the formation of metastable nitride thin films that are otherwise challenging to obtain. For example, we have synthesized Ta3N5 films derived from metastable Ta2N3 precursors. These films naturally incorporate sub-nitride impurities near the substrate interface, which facilitate electron transport and allow a 100 nm Ta3N5 photoanode to outperform much thicker oxide-derived counterparts. This approach enhances photoelectrochemical performance while reducing tantalum usage, opening a scalable route toward efficient nitride-based solar energy conversion.

Originally developed for water splitting and solar fuel production, photoelectrochemical methods are now emerging as powerful tools for organic synthesis. Photoelectrodes can not only replace traditional organometallic catalysts but also offer distinct reaction selectivity under light-driven conditions. Our group investigates the electron transfer kinetics and surface reaction mechanism that govern these processes, aiming to reveal how photoexcited carriers mediate selective chemical transformations and to expand the scope of light-driven synthetic chemistry.

Ternary oxides are promising materials for photoelectrochemical energy conversion because of their chemical robustness, low fabrication cost, and tunable optoelectronic properties. However, understanding their intrinsic charge transport—particularly polaronic conduction—is often hindered by the grain boundaries present in conventional polycrystalline thin films. Our group has developed a chemical solution epitaxy approach that enables the growth of highly oriented, epitaxial thin films of complex metal oxides using a cost-effective, scalable process. This method minimizes grain boundary density and provides well-defined crystallographic control, allowing us to probe anisotropic charge transport and carrier dynamics with unprecedented clarity.