Using X-Rays, Prof. Joel Brock, applied engineering and physics, explores electrochemical processes in solid state materials, especially complex oxide thin films.
A thin film is a layer of material ranging from fractions of a nanometer to micrometers in length. Metal oxides exhibit a host of interesting and useful phases of matter, such as high temperature conductivity; quantum magnetism, magnetic properties at the atomic level that are dependent on electron spin states; and multiferroic behavior, the ability to become a permanent magnet.
According to Brock, the crystal arrangements of oxygen and metallic ions in the oxides support electronic interactions and allow oxides to assume a range of different arrangements.
Brock studies pulsed laser deposition of films comprised of complex oxides. In PLD systems, pulses from a focused laser shoot out UV light. This light vaporizes the surface of the material and converts it to plasma, which then reverts back to a gas before it reaches the reactants.
Using X-Rays from the synchrotron light source, Brock observes the structure of the atomic layers during the formation of the film, facilitating an in-depth understanding of the kinetics of the reaction and how the chemicals are distributed on the surface of the film.
“When I heard about this 15 years ago, I thought this is crazy,” Brock said, “It’s like taking mud and rocks, throwing it at the garage door, and getting the Mona Lisa. It doesn’t seem possible.”
The desire to manufacture smaller electronic devices, often on the nanometer length scale, has driven an effort to control the chemical makeup and structure of thin films used in integrated circuits.
In addition to PLD, Brock uses X-Rays to study electrochemical processes using oxide materials as catalysts to propagate photocatalytic water splitting reactions, or the dissociation of water into hydrogen and oxygen using light as a catalyst.
These methods are being investigated in order to create hydrogen fuel cells, which burn cleanly, and have positive ramifications for the rise of alternative energy sources according to Brock.
Brock’s project studies strontium titanate, SrTiO3, and observes how successful it is at catalyzing water-splitting reactions. Strontium titanate is a stable compound, but it is reactive enough that, with light, it may be able to catalyze the water-splitting reaction. At the moment, the lab has only managed to carry out the reaction splitting a very basic solution, such as Liquid Drano.
Currently, most materials that can split water absorbs light in the UV spectrum range. The next step in the project is to continue altering the conditions under which the reaction occurs, until the reaction absorbs light from a different energy range, such as solar radiation. Brock is optimistic that once there are enough experiments conducted, the result will be a fuel cell that, through the photocatalytic water-splitting reactions, takes in solar radiation and gives out clean water and power as products.
“There is good reason to think that in the next four to five years, we could hear news about materials that can absorb solar radiation, which would be really exciting given the current energy crisis,” Brock said.
The machine responsible for the X-Ray experiments that Brock investigates is Cornell’s High Energy Synchrotron Source. A synchrotron is a large machine, about the size of a football field, that accelerates electrons close to the speed of light. As the electrons are deflected using magnetic fields, they create a very bright light, which is channeled into experimental stations, where it is then used for research. Light from the synchrotron can be generated from the whole electromagnetic spectrum, from infrared light to X-Rays.
Brock currently serves as associate director of the synchrotron, and this coming summer, he will be director of the G-Line Division at CHESS, the facility that houses the synchrotron. The facility caters to hundreds of scientists every year, from a wide range of disciplines, from biology and chemistry to applied physics and materials science.
CHESS runs projects as diverse as developing new sources of X-Rays to enhance the technology of beams to using the synchrotron’s beams to detect chemicals in the inner-ear bones of fish to give insight as to what environments the fish have encountered over a period of time.
Brock is not teaching at Cornell this semester, but he has taught various courses in applied engineering and physics, including statistical mechanics, electricity and magnetism, and advanced experimental physics. He enjoys interacting with students who truly want to learn, especially when he gets the opportunity to work with them one on one, he said.