Sniffing out hazards
“There’s a continuing need for the development of sensitive, selective and low-cost sensors for applications in a wide range of manufacturing, processing and power generating industries,” Akbar said. “Over the past 20 years, our focus has been on the development of a series of high-temperature gas sensors specifically for combustion processes such as in automobile engines and heat-treating furnaces. We’ve recently moved toward air quality monitoring applications.”
Akbar credits foundational work by PhD candidate Derek Miller for the basis of Akbar and Morris’s successful proposal to the NSF’s Division of Materials Research which will result in $732,975 in funding over four years. Miller wondered why some sensors were more successful than others.
“In the summer of 2013, I began a literature review on all of the different combinations of metal oxides that were being used as gas sensors,” Miller said. “The combinations typically used a few possible materials in one sensor, and combined these materials in many different forms on the nanoscale.”
Some would merely mix nanoparticles, some would put a thin coating of one oxide onto nanowires of another oxide. More intricate combinations – hierarchical heterostructures -- were also created that often looked like flowers or pine trees. These papers all seemed to give unique and promising results.
“However, it was apparent that the literature was not really building on itself and the studies were mostly trial-and-error, making any combination of materials they could and testing them against every gas they had,” Miller said. “Very few studies actually did the proper measurements to figure out the reasons for the improved performance.”
He framed his project to address this issue, and was awarded a NASA Space Technology Research Fellowship to carry out the work.
“NASA is obviously interested in gas sensors to monitor space-based habitats for safety of the astronauts,” Miller noted. He said the published literature review has garnered about 170 citations in two years, which is quite fast even for a review paper and “shows that it addressed a real problem in the literature. My project has focused on two parts – electrical measurements and electron microscopy characterization.”
The characterization aspect utilized unique capabilities found at Ohio State’s Center for Electron Microscopy and Analysis (CEMAS).
Akbar and Miller are aiming for a complete picture of electronic structure at the interface that helps determine what happens to electrons and holes in these heterostructures–which is the key to understanding why the structures have enhanced performance. These theories will then be tested out experimentally using new equipment on order funded by the NSF grant.
Another aspect of the NSF project is the construction of an open-access database to serve as a depository of published gas sensor literature using these types of materials. Once complete, this database will allow for searching and filtering of actual data, not just the publication details.
“We envision the open-access database to aid the gas sensor researcher in evaluating the current state-of-the-art, the most notable deficiencies in need of study, and to aid the commercial manufacturer in selecting the most promising systems for specific applications,” Miller said.
The Open-access Database of Resistive-type Gas Sensors (ODORS) will help establish Ohio State as a leader in the gas sensor field and peers in other countries will be encouraged to help keep the database up-to-date with work published from their respective regions. “A database such as this is long overdue in this field given the nature of the data produced,” Akbar said.
“We hope that this will allow researchers to quickly compare many similar papers and find trends that are otherwise not obvious when reading many papers from different groups separately,” Miller said.
Miller will complete his NASA fellowship when he graduates in Spring 2017, but work on the NSF project will continue with future students.