right|frameless The original form of the electron microscope, the transmission electron microscope (TEM), uses a high voltage electron beam to illuminate the specimen and create an image. An electron beam is produced by an electron gun, with the electrons typically having energies in the range 20 to 400 keV, focused by electromagnetic lenses, and transmitted through the specimen. When it emerges from the specimen, the electron beam carries information about the structure of the specimen that is magnified by lenses of the microscope. The spatial variation in this information (the "image") may be viewed by projecting the magnified electron image onto a detector. For example, the image may be viewed directly by an operator using a fluorescent viewing screen coated with a phosphor or scintillator material such as zinc sulfide. A high-resolution phosphor may also be coupled by means of a lens optical system or a fibre optic light-guide to the sensor of a digital camera. Direct electron detectors have no scintillator and are directly exposed to the electron beam, which addresses some of the limitations of scintillator-coupled cameras.
RighT|framEless tHE original foRm Of the ElectRon miCrosCOpE, thE TraNsMissIon eLeCtrOn mICrosCOPe (teM), USes a higH voltagE eLectrOn beam tO IllUMiNAte tHE SPeCiMeN and crEAtE AN image. aN electroN BEam Is prODuced bY aN Electron Gun, With thE ElecTronS Typically having energiES in thE Range 20 to 400 kEv, focUsed by eLeCTrOMaGnetic LenSes, And tranSmitted ThroUgh the specImen. WhEn it emERges frOm The SpeciMen, ThE elEctRon bEam carrIEs informaTIoN abouT thE strUctuRe OF the SpeCimEn that is mAgNIfied by lENseS Of thE mIcrosCope. thE spatIal VaRiaTiON in this InfOrmATion (thE "iMage") may be ViEwed by pRojecting the MaGnifieD eLeCTrON imagE ontO a deTecTOr. For examPlE, tHe ImagE May be vieWed direcTLY by An oPerator usINg a FLuOrescEnt viewinG scrEeN coatEd With A PhospHoR OR scInTiLlatOR matEriAl suCH As zinc Sulfide. a high-ResOLUtion phOsPhor mAy alSo bE coupled by means Of A lENs oPtIcal sysTeM OR A fibre optic light-Guide to the sENSOR OF a DIgiTaL cAmera. Direct ELectRon DetectorS HAVE No scintillaTOr ANd Are directly exposED to the elECTron beam, wHich aDDrEsses sOme of tHe liMItatioNs of scintillaTor-CoupleD caMEras.