Transmission Electron Microscopes (TEM)
TEMs transmit a beam of electrons through a thin specimen (<100nm), interacting with the specimen as it passes through. The interaction forms an image which is magnified and focused, then projected onto a phosphor screen for viewing. Images can then be captured with CCD cameras at various locations above and below the screen.
Analytical information can also be sampled with other detectors such as in Electron Energy Loss Spectroscopy (EELS), Energy Dispersive X-ray analysis (EDX), and automated crystal orientation mapping (ACOM). The beam may also be scanned over an area, using a scanning TEM detector (STEM).
TEMs are capable of imaging at sub-nm spatial resolution; significantly better than both SEMs and light microscopes, owing to the small de Broglie wavelength of electrons. This enables the instrument to examine fine detail - even as small as a single column of atoms, which is thousands of times smaller than the smallest resolvable object in a light microscope.
TEM imaging is a major analysis method in a range of scientific fields, in both physical and biological sciences. TEMs find application in cancer research, virology, materials science as well as pollution, nanotechnology, and semiconductor research.
At smaller magnifications TEM image contrast is due to absorption of electrons in the material, due to the thickness and composition of the material. At higher magnifications complex wave interactions modulate the intensity of the image, requiring expert analysis of observed images. Alternate modes of use allow for the TEM to observe modulations in chemical identity, crystal orientation, electronic structure and sample induced electron phase shift as well as the regular absorption based imaging.