Norman Mannella

UTK physics and astronomy

As fossil fuels have dwindled in the modern age and their combustion has begun to adversely affect climate and the environment, the search for dramatically more efficient and less expensive solar energy conversion technologies has become a driving force behind research in nanomaterials.

As yet, no major breakthrough in the conversion efficiency of materials used in photo-electrochemical applications has been achieved, limiting photo-catalysis efficiency well below the ten percent target for commercial and industrial applications.

In a path-breaking step to address this challenge, JDRD team leader Norman Mannella partnered with the LDRD team headed by Zhenyu Zhang at ORNL. Combined expertise from the two teams integrates advanced materials synthesis with a fundamental understanding of materials properties for new high-efficiency solar energy applications—all guided by predictive theoretical modeling and simulations.

In the basic experimental approach chosen for this work, Mannella and graduate research assistant Amal Al Wahish use a technique known as molecular beam epitaxy (MBE) to grow high quality titanium oxide (TiO2) thin films in a state-of-the-art chamber, where they can probe and characterize the structural, electronic, and chemical properties of the resulting films without removal (and so without the contamination that would result).

JDRD Project: Doping control of epitaxial TiOx and TiO2 thin film hetero-structures for photo-electrochemical solar energy conservation;
LDRD Project: Bandgap narrowing of oxide semiconductors using non-compensated n-p Co-doping for enhanced solar energy utilization, Zhenyu Zhang.

In a process known as “doping” the researchers intentionally add impurities to the transition metal oxide material, in an effort to “narrow the band gap.” The team employs two novel doping schemes while leveraging the unique advantage of the MBE system to precisely control the structure and composition of the films.

In recognition of the potential in this line of inquiry, Mannella has recently been awarded his first National Science Foundation research grant in support of a major effort on growing thin film transition-metal oxides with MBE.

Schematic drawing of the MBE system in Mannella’s Laboratory in UTK’s Science and Engineering Facility. The MBE chamber is connected to a photoemission chamber with the ultrahigh resolution Scienta R4000 spectrometer and a variable temperature scanning transmission microscope (VTSTM).