Ceria Monitors: Ultrasensitive oxygen sensor towards energy sustainability
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Ceria Monitors: Ultrasensitive oxygen sensor towards energy sustainability
R. Sanghavi1, M. Nandasiri2, 3, S. Kuchibhatla2, P. Nachimuthu2, M.H. Engelhard2, V. Shutthanandan2,
W. Jiang2, #, S. Thevuthasan2, A. Kayani3, S. Prasad1
1Department of Electrical, Computer and Energy Engineering, P.O. Box 875706, Arizona State University , Tempe, AZ 85287, USA
2 EMSL, #Pacific Northwest National Laboratory, Richland, WA 99354, USA,
3 Physics Department, Western Michigan University, Kalamazoo, MI 49008, USA
Poster Abstract: In developing energy efficient and sustainable automobile or industrial processing systems, one of the key components that requires sophisticated monitoring is the amount of trace oxygen within the combustion system. Hence, portable, stable and sensitive oxygen sensors are required for applications in automobile industry, wherein, the sensors operate at high temperatures to measure the oxygen concentration at the exhaust systems of the automobiles. To design a simple, compact, fast and sensitive oxygen sensor, we have identified, characterized and optimized the material system that would potentially function as the active sensing material for such an oxygen sensor.
In order to develop oxygen gas sensors based on Samaria Doped Ceria (SDC) thin films, it is important to understand the influence of dopant concentration, film thickness and the crystalline quality on the electrical properties of the active sensing material. We have recently established that 6 atom % Sm doping in ceria films has optimum conductivity. Based on this observation, we have studied the variation in the overall conductivity of these thin films as a function of thickness in the range of 50 nm to 300 nm at a fixed bias voltage of 2 volts. We observed saturation in the conductivity above 200 nm up to 300 nm film thickness. We have identified that the hysteresis error and the dynamic response of this oxygen sensor is generic for the material system and is independent of the sensing film thickness. For oxygen pressure values of 1 mTorr to 100 Torr, a tolerable hysteresis error, good dynamic response is observed. The influence of the grain boundaries on the conductivity was studied by growing single crystal epitaxial thin films and polycrystalline thin films with the similar thickness and the Sm concentration.
A hypothesis on the increase in the conductivity of the sensing material as well as the saturation in the increase in conductivity with the increase in the (SDC) film thickness above certain thickness will be discussed. Furthermore, the development of four probe conductivity measurement system of the oxygen sensing material will be discussed. This study can be used to design an oxygen sensor, maximizing the overall efficiency by optimizing the sensing film concentration, thickness and crystalline quality with the constraints on the sensor response time and overall power consumption.
