ELECTRONIC MICROSCOPY AND MATERIAL MICROANALYSIS

Scanning Electron Microscopy

The images obtained by scanning electron microscopy, they provide both topographic information of the surface of a rough sample (fracture facies, coatings, micro-threads etc.) and qualitative information on compositional differences, or crystal orientation of a sample polished. The R-X emission spectra of the sample, which can be purchased both with the EDX detector as WDX detectors give both qualitative and quantitative information on the composition of a sample point, a line or a small surface the same. Thus it is possible, on the one hand to determine the chemical formula of each of the phases present in the sample and observing the segregation of elements, provided that these do not occur in a submicron scale. Furthermore, the diffraction patterns of Kikuchi bands obtained with EBSD detector, can recognize crystal structures and thereafter determine both the misorientation between adjacent crystals, such as obtaining microtextures produced during the treatment of the sample under study etc. You can also simultaneously, looking forward to obtain compositional and crystalline information simultaneously over multiphasic samples, obtainEDX maps and EBSD maps .

Transmission Electron Microscopy

Electron microscopy of transmission, provides information both in image as in diffraction of the same point of the sample and this information can be acquired for different inclinations of the sample, relative to the electron beam. This property gives it great versatility, as it can be characterized with both crystalline defects (dislocations, grain boundaries) and compositional (antiphase boundaries, precipitates, segregations etc.) and the crystal structure. Being able to make convergent beam diffraction (CBED),is able to determine the crystal cell, the point group and space group of crystals, micro and nano imbued , or not, in a larger sample size. Moreover, EDX spectra (obtained by the photon emission of RX) and EELS spectra (obtained as a result of the loss of energy of electrons passing through the sample), which can be acquired on different points of the sample, allow to determine chemical formulas of the phases under consideration, that can be nano-sized. Furthermore, when the transmitted beam sweeps the sample it can be obtained distribution maps of elements that can give compositional information, even at the level of an atomic column if this is sufficiently separated from its adjacent (in our team Titan Cubed distance, between atomic columns must be greater than 0.135nm). The images are acquired in high resolution due to the interference of different diffracted beams and the transmitted beam and give information about the atoms that constitute the unit cell, as long as the sample is thin enough (two or three dozen nm) and the results of the series of focus, obtained experimentally, with simulated images are compared. 0.07nm resolution allows to determine a number of crystalline structures provided as, again, the samples are adequate. The resolution of 0.135nm STEM with HAADF detector mode, allows to see compositional differences in different atomic columns, again if the samples have adequate preparation and guidance, if not the case compositional differences between nanometric phases will only be observed.

FIB

The FIB which is provided, is a computer that contains two columns one for electrons and one for  ion forming a known angle. It allows to prepare samples of a wide variety of materials (metals, ceramics, semiconductors) for observation in a transmission electron microscope, being these lamellae, of substantially parallel faces, and thicknesses which  can be controlled. The sample size is typically about 20mm long by about 5 mm of width and thickness depends on the type of information required and the density of that sample.