MS Thesis Presentation by Lisa M. Ellis
Tuesday, July 6, 2004

(Dr. Steven Danyluk, Chair )

"Monitoring Oil Quality with Optically Stimulated Contact Potential Difference Sensor"


This thesis validates the concept of using an optically stimulated Contact Potential Difference (osCPD) sensor to monitor oil degradation. The osCPD technique is a variant of the contact potential difference (CPD) method used to obtain surface properties of materials. The new approach uses AC modulated light to stimulate electron charge carriers in silicon coated with a layer of oil. Demonstration of this oil monitoring technique was done by placing different oil samples that had degraded due to use in an engine on the silicon surface and monitoring the corresponding electrical signal from the osCPD sensor.

Experiments showed that the osCPD sensor produced an electrical signal that was related to the amount of time oil was used in an engine (or mileage). It is believed that the osCPD signal is dependant on the charge transfer at the silicon and oil interface. Investigation of this interaction was carried out by creating a passivating layer on the silicon surface. This passivation layer separates the silicon and oil and thereby eradicates the charge transfer process between the two. Experiments show that adding the nitride layer eliminated the change in osCPD electrical signal with mileage. This supports the belief that a change in signal due to mileage is caused by a charge interaction between the oil and silicon. A model of this charge interaction will also be shown.