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Ewalds Sphere construction for electron and X-ray radiation.īecause the radius of the Ewalds sphere (1/ l ) of the electron beam is large in comparison to the reciprocal lattice, (along with beam convergence and small variations in l ) you are assured to produce diffraction off multiple planes. If the material of interest has a lattice parameter of a o = 3.6Å, a*=0.278Å -1įigure 2. So you are only observing a very small portion of the material.
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The material must be less than 200 nm thick in order to pass the electron beam through. Limitation of TEM: Sample size and preparation. compositional analysis of individual phases imaging atomic planes and defects in packing associated with dislocations or interfaces determining the growth directions of precipitates or lamella in the material and the type of interfaces between different phases (i.e. determining site occupancy preferences of the atoms in the crystal structures characterizing and identifying defects (antiphase boundaries, dislocations, stacking faults) in the crystal structure and to determine modes of deformation (identifying the slip systems of a material or mode of failure) identifying the phases and crystal structures present in the material composition analysis of individual phases imaging regions or phases of different chemical composition surface topography and analysis of fracture surfaces This type of x-ray production in the sample is the same principle as that of the generation of x-rays used in x-ray diffraction instruments.įigure 1. Detectors in both SEM and TEM instruments collect the characteristic x-rays that are generated from the sample to allow for compositional analysis of the material. In a TEM, the electron beam passes through the sample and produces an image using the transmitted electron beam which contains both diffracted and unscattered electrons. A SEM uses the electrons that are scattered off of the sample surface to produce images of the sample. The electron microscopes also use the many interactions that the electron beam has on the sample (Figure 1) to produce various imaging and diffraction modes that can be used to analyze the material down to the atomic scale. Electron microscopes, such as the scanning electron microscope (SEM) and transmission electron microscope (TEM) are instruments used in the analysis of materials on a scale much smaller than possible by optical microscopy.