A 9 GHz EPR imager for thin materials: application to surface detection.

A 9 GHz EPR imager that is capable of the imaging surface area of thin materials has been built. The EPR imager resolved samples spaced 1 mm apart. The developed TE(111) cavity was able to detect easily ~1.0 mM aqueous TEMPOL solution in ~1.0 mm (i.d.) glass capillary placed just above the cavity. The sensitivity measured using the TEMPOL solution showed ~0.3 of that for the modified JEOL cavity, which was in a qualitative agreement with the calculations considering the difference in the filling factors of the cavities. The relatively low measured sensitivity of the TE(111) cavity is due to utilization of the microwave field from ~3 mm aperture (hole) in the cavity wall. More importantly, the TE(111) cavity does not require inserting the sample into the cavity and placing samples into EPR tubes.