Editing Scanning electron microscope (section)

==Resolution of the SEM==
[[File:SEM Zoom.ogv|thumb|A video illustrating a typical practical magnification range of a scanning electron microscope designed for biological specimens. The video starts at 25×, about 6 mm across the whole field of view, and zooms in to 12000×, about 12&nbsp;[[μm]] across the whole field of view. The spherical objects are glass beads with a diameter of 10&nbsp;μm, similar in diameter to a [[red blood cell]].]]
A SEM is not a [[camera]] and the detector is not continuously image-forming like a [[Charge-coupled device|CCD]] array or [[Photographic film|film]]. Unlike in an optical system, the [[Optical resolution|resolution]] is not limited by the [[diffraction limit]], fineness of lenses or mirrors or detector array resolution. The focusing optics can be large and coarse, and the SE detector is fist-sized and simply detects current. Instead, the spatial resolution of the SEM depends on the size of the electron spot, which in turn depends on both the wavelength of the electrons and the electron-optical system that produces the scanning beam. The resolution is also limited by the size of the interaction volume, the volume of specimen material that interacts with the electron beam. The spot size and the interaction volume are both large compared to the distances between atoms, so the resolution of the SEM is not high enough to image individual atoms, as is possible with a [[transmission electron microscope]] (TEM). The SEM has compensating advantages, though, including the ability to image a comparatively large area of the specimen; the ability to image bulk materials (not just thin films or foils); and the variety of analytical modes available for measuring the composition and properties of the specimen. Depending on the instrument, the resolution can fall somewhere between less than 1&nbsp;nm and 20&nbsp;nm. As of 2009, The world's highest resolution conventional (≤30&nbsp;kV) SEM can reach a point resolution of 0.4&nbsp;nm using a secondary electron detector.<ref>[http://www.nanotech-now.com/news.cgi?story_id=42612 Hitachi Launches World's Highest Resolution FE-SEM]. ''Nanotech Now''. 31 May 2011.</ref>