Graphene is at the atomic limit of thinness: a single layer of crystalline, hexagonally bonded carbon. Yet real-world samples usually contain defects, which are challenging to visualize. For graphene layers grown on or transferred to a transparent substrate, conventional light microscopy achieves an image contrast of only 2%. Ke Xu and his group at the University of California, Berkeley, have developed a new visualization approach based on interference reflection microscopy (IRM), a label-free optical technique originally developed for cell biology. When applied to graphene on a transparent substrate, the technique can distinguish layers with a contrast greater than 30% and allows in situ monitoring at up to 100 frames per second.
This image, generated by IRM using filtered green light from a broadband lamp, shows a 62 μm × 77 µm section of a graphene layer grown by chemical vapor decomposition and deposited on glass. Voids (white regions), cracks (white...
