Electron Microscopy for High Resolution Imaging
Electron microscopes come in two broad varieties: transmission electron microscopes (TEMs) and scanning electron microscopes (SEMs). Both instruments provide high-resolution imaging and 1-D and 2-D compositional information.
SEMs provide surface images and information about topography by scanning the sample with a focused beam of electrons and monitoring the commisurate secondary electron signal. High-contrast images using backscattered primary electrons (EBSD) can provide general information about atomic mass. An energy dispersive X-ray detector (EDS) on the SEM gives elemental composition with excellent spatial resolution (~10 nm) and an information depth of ~ 5 microns. Cathodoluminescence images from electron-induced UV-visible fluorescence can provide real color data. Sample composition can be found at a point, series of points, across a line or over an area.
TEMs provide nanoscale or atomic-scale images of thin sections of a material, where high-energy electrons pass through the sample to form the image or provide crystal structure information, including phase. The narrow beam of electrons can also provide elemental information via EDS as a function of position (maps). The addition of an electron spectrometer on our TEM allows electron energy loss spectroscopy (EELS) for measurement of atomic composition (particluarly light elements), chemical bonding, and valence and conduction band electronic properties.