Scanning electron microscopy (SEM) is an imaging technique that is used to produce high resolution surface images of a sample. In SEM, the sample is bombarded with electrons from an electron gun. The electron beam is raster across the sample and secondary electrons and back scatter electrons can be observed to form the final image. SEM can provide a resolution of better than one nanometer. The technique can be used to image any solid sample that fits onto the specimen holder. It has been more recently employed to image biological samples as well. SEM instruments can be coupled with detector systems such as energy dispersive x-ray spectroscopy (EDS or EDX). This provides elemental information about the composition of the sample surface. SEM instruments range in size from benchtop instruments to large free standing models. The technology is mature.