Surface plasmon sensors on ZnO:Ga layer surfaces: Electric field distributions and absorption-sensitivity enhancements

Surface plasmon resonances (SPRs) on ZnO:Ga layer surfaces (ZnO-SPR) enhanced absorption bands related to molecular-vibrations (OH and CH3 modes) in the near-infrared range by controlling layer thickness. These behaviors were due to the interaction between SPR excitations and molecular vibrations. Further investigation revealed that the high detection sensitivity of SPRs on ZnO:Ga layer surfaces was 6837 nm/RIU using water and methanol mixtures. The detection region of ZnO-SPR was limited within several hundred nanometers from the layer surfaces, which is discussed relative to theoretical analysis of field distributions and spatial coherence of SPRs on ZnO:Ga layer surfaces.