Flexible incidence angle scanning surface plasmon resonance microscopy for morphology detection with enhanced contrast

Abstract

Surface plasmon resonance microscopy (SPRM) has been massively applied for near-field optical measurement, sensing, and imaging because of its high detection sensitivity, nondestructive, noninvasive, wide-field, and label-free imaging capabilities. However, the transverse propagation characteristic of the surface plasmon wave generated during surface plasmon resonance (SPR) leads to notable “tail” patterns in the SPR image, which severely deteriorates the image quality. Here, we propose an incidence angle scanning method in SPRM to obtain a resonance angle image with exceptional contrast that significantly mitigates the adverse effects of “tail” patterns. The resonance angle image provides the complete morphology of the analyzed samples and enables two-dimensional quantification, which is incapable in conventional SPRM. The effectiveness of the method was experimentally verified using photoresist square samples with different sizes and two-dimensional materials with various geometric shapes. The edges of samples were fully reconstructed and a maximum fivefold increase in the image contrast has been achieved. Our method offers a convenient way to enhance the SPRM imaging capabilities with low cost and stable performance, which greatly expands the applications of SPRM in label-free detection, imaging, and quantification.