ORNL’s material scientists developed a synthesis strategy for discovering novel complex-oxide thin films for stronger solar light absorption.
light emitting diodes, displays and other electronic devices could get a
bump in performance because of a discovery at the Department of
Energy’s Oak Ridge National Laboratory that establishes new boundaries
for controlling band gaps.
complex transition metal oxides have for years held great promise for a
variety of information and energy applications, the challenge has been
to devise a method to reduce band gaps of those insulators without
compromising the material’s useful physical properties.
band gap is a major factor in determining electrical conductivity in a
material and directly determines the upper wavelength limit of light
absorption. Thus, achieving wide band gap tunability is highly desirable
for developing opto-electronic devices and energy materials.
a layer-by-layer growth technique for which Ho Nyung Lee of ORNL earned
the Presidential Early Career Award for Scientists and Engineers, Lee
and colleagues have achieved a 30 percent reduction in the band gap of
complex metal oxides. The findings are outlined in the journal Nature
approach to tuning band gaps is based on atomic-scale growth control of
complex oxide materials, yielding novel artificial materials that do
not exist in nature,” Lee said. “This ‘epitaxy’ technique can be used to
design entirely new materials or to specifically modify the composition
of thin-film crystals with sub-nanometer accuracy.”
band gap tuning has been widely successful for more conventional
semiconductors, the 30% band gap reduction demonstrated with oxides
easily surpasses previous accomplishments of 6%—or 0.2 eV—in this area
and opens pathways to new approaches to controlling band gap in
this discovery, the potential exists for oxides with band gaps to be
continuously controlled over 1 electron volt by site-specific alloying
developed by the ORNL team. “Therefore,” Lee said, “this work represents
a major achievement using complex oxides that offer a number of
advantages as they are very stable under extreme and severe
Michelle Buchanan, associate lab director for the Physical Sciences
Directorate, expanded on Lee’s sentiment. “This work exemplifies how
basic research can provide technical breakthroughs that will result in
vastly improved energy technologies,” she said.
authors of the paper, titled “Wide band gap tunability in complex
transition metal oxides by site-specific substitution,” are Woo Seok
Choi, Matthew Chisholm, David Singh, Taekjib Choi and Gerald Jellison of
ORNL’s Materials Science and Technology Division. A patent is pending
for this technology.
research was funded initially by the Laboratory Directed Research and
Development program and later by the Department of Energy’s Office of
Science. Optical measurements were performed in part at the Center for
Nanophase Materials Sciences, a DOE-BES user facility at ORNL.