AFM was not the only device used in my PhD project to measure surface forces. We also used another powerful technique/device, called SFA (Surface Force Apparatus). SFA provides high resolution direct force measurements between two contacting surfaces in fluids, based on optical interferometry  . It contains two opposing cylindrical shaped disks (shown schematically in the left bottom figure) where micrometer thick samples (with semireflective coating on their back) are mounted on each disk. The separation between these two surfaces (D), interaction forces and surface deformations are measured through analysis of the optical interference fringes that result from white light passing through the opposing surfaces. They are known as fringes of equal chromatic order (FECO), shown in the top left image. More detail about this part of my work can be found here  .