ZnO sensing film thickness effects on the sensitivity of surface plasmon resonance sensors with angular interrogation

The effects of ZnO sensing film thickness on the surface plasmon resonance (SPR) curve have been investigated. ZnO sensing films with the thickness of 20 nm, 30 nm, 200 nm, 220 nm and 240 nm have been deposited onto Ag/glass substrates by radio frequency magnetron (RF) sputtering and thermally treated at 300 °C in air for 1 h. The surface morphology of the sample was inspected using an atomic force microscope (AFM). The refractive index of the ZnO films was extracted by using spectroscopic ellipsometry (SE). Theoretical analysis of the sensitivity of the SPR sensors with different ZnO sensing film thickness is discussed, and the experimental results are in agreement with the calculated value. Also, the theoretical calculation of the effects of ZnO film thickness on the SPR curves in the presence of different analytes are presented and studied. It is demonstrated that SPR sensors with angular interrogation may attain higher sensitivity and can detect higher surface environment refractive index with proper ZnO sensing film thickness.