Energy-Filtered Transmission Electron Microscope (EFTEM)

 Energy-filtering transmission electron microscope (EFTEM), developed about ten years ago, is now a routine analysis tool in the characterization of materials.

 It is a technique used in Transmission electron microscopy, in which only electrons of particular kinetic energies are used to form the image.  The ability of an energy-filter to show a two- dimensional distribution of a specific element.  The images at an energy-loss between 100 and 200 eV.

 If a very thin sample is illuminated with a beam of high-energy electrons, then a majority of the electrons will pass through the sample but some will interact with the sample, Scattered elastically or in elastically, Inelastic scattering results in both a loss of energy and a change in momentum

 If the electron beam emerging from the sample is passed through a magnetic prism, then the flight path of the electrons will vary depending on their energy.  It is possible to place an adjustable slit to allow only electrons with a certain range of energies through, and reform an image using these electrons on a detector.  The energy slit can be adjusted so as to only allow electrons which have not lost energy to pass through to form the image.

 It consists of two main parts:  Magnetic prism  Optical column

 In the curved magnetic field, electrons with different energies are dispersed, obtained at the end of this part.  The magnetic prism is the same as in a parallel electron energy loss spectrometer

 An energy range is selected by a slit located at the dispersion plane.  In imaging mode, and an energy-filtered image occurs at the end of the GIF, where a slow-scan CCD camera is installed for image recording.

 Spatial resolution refers to the size of the smallest object that can be resolved on the ground.  In a digital image, the resolution is limited by the pixel size, i.e. the smallest resolvable object cannot be smaller than the pixel size.  The spatial resolution obtained in an EFTEM image is influenced by the specific details of the experiment itself:

 When doing EFTEM at high magnifications elastic contrast that is always present in EFTEM images may become visible. as th collection angle.

 Energy filtering can be applied for various problems:  Zero-loss filtering :  Electron spectroscopic imaging :

 Zero-loss filtering removes the contribution  of all in-elastically scattered electrons to both images and diffraction patterns.  By using only the zero-loss beam, all in elastically scattered electron are omitted (reduction of noise).  That leads to increased contrast and the resolution in TEM images.

 By using electrons with a well-defined energy loss (ionization edge), elemental distribution maps can be generated.