Post-it note. Coloured scanning electron micrograph (SEM) of spheres of adhesive (yellow) on the back of a Post-it note. The spheres contain an adhesive. They rupture under pressure, releasing a thin film of adhesive over the surface they are in contact with. Only a few spheres are ruptured at one time, meaning the Post-it note can be reused many times until all the spheres have been exhausted. Magnification unknown.