Scanning tunneling microscopy (STM), also called a scanning probe microscopy, was developed in the 1980s to explore the surface structure of specimens at the atomic level. This technique uses electronic methods to move a metallic tip (a conducting material such as platinum-iridium), composed ideally of a single atom, across the surface of a specimen. As the tip is moved across the surface of the specimen, electrical voltage is applied to the surface. If the tip is close enough to the surface and the surface is electrically conductive, electrons will begin to leak or “tunnel” across the gap between the probe and the sample. The tip of the probe is automatically moved up and down to maintain a constant rate of electron tunneling across the gap as the probe scans the sample. The movement is presented on a video screen. Successive scans then build up an image of the surface at atomic resolution.