Contrast Mechanisms of Solution-Dispersed GrapheneCompounds in Twilight Fluorescence Microscopy

Twilight fluorescence microscopy is a newly developed technique that is capable of imaging a single layer graphene compound dispersed in a liquid. A graphene solution is mixed with a highly concentrated dye solution and the mixture is placed on a glass plate. An excitation beam enters the glass/solution interface with the incident angle that has a finite width around the total internal reflection angle, allowing a faint refracted beam to be transmitted into the solution phase. Furthermore, the propagation distance of the refracted beam is limited by the inner filter effect due to strong absorption of the concentrated dye. The fluorescence lights excited by both the evanescence field and the refracted beam decay exponentially as they travel from the glass surface and are used as a microscope illumination. In this study, the decaying length of each excitation light is measured. A simplified theory for dark contrast of graphene compounds is developed based on absorption and Forster resonance energy transfer ...