Simple Optical Imaging of Nanoscale Features in Free-Standing Films

Measuring thicknesses in thin films with high spatial and temporal resolution is of prime importance for understanding the structure and dynamics in thin films and membranes. In the present work, we introduce fluorescence-interferometry, a method that combines standard reflected light thin film interferometry with simultaneous fluorescence measurements. We apply this method to the thinning dynamics and phase separation in free-standing inverse phospholipid bilayer films. The measurements were carried out using a standard fluorescence microscope using multichannel imaging and yielded subnanometer resolution, which is applied to optically measure the discrete thickness variations across phase-separated membranes.