Scanning electron microscope. Researcher looking at a sample using a scanning electron microscope (SEM). An SEM uses an electron beam to obtain a three-dimensional image of an object. The beam is scanned over the sample in a vacuum, causing the emission of secondary electrons. These secondary electrons are detected and used to form the image. The sample here is material from a fossilised footprint found in rock on the Roccamoufina Volcano, near Naples, Italy. It is part of a set known locally as the 'Devil's tracks'. The footprints have been identified as human and dated to between 385,000 and 325,00 years ago. Photographed at the University of Naples, Italy.