at the top picture of:
http://physicsworld.com/cws/article/news/2014/apr/08/atom-thin-sheets-are-transferred-with-ease
he is holding a layer of material (of graphene in this case ) just one-atom thick and about 1cm by 1cm in 2D area, with tweezers and that layer, despite being only one atom thick, is clearly visible with the unaided eye -I find that quite remarkable.