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Microscopic techniques (EDXA (Energy Dispersive X-Ray Analysis (EDX is an…
Microscopic techniques
SEM
Scanning electron microscope A scanning electron microscope (SEM) produces images by detecting secondary electrons which are emitted from the surface due to excitement of the primary electron beam, SEM can produce detailed images of the surfaces of cells and whole organisms that are not possible with TEM. It can be used for particle counting and size determination, (University of Massachusetts Medical School, 2018)
The SEM is widely used to identify phases based on qualitative chemical analysis and/or crystalline structure and to generate high- resolution images.
Metal samples can be examined with the SEM to determine strength in different conditions such as cold and heat.
The SEM generates a beam of electrons above the sample chamber, these electrons are produced by a thermal emission source (e.g. a heated tungsten filament). The electrons are focused into a small beam by a series of electromagnetic lenses in the SEM column. Scanning coils near the end of the column direct and position the focused beam onto the sample surface. The electron beam is scanned over the surface for imaging, and the emitted electrons are detected for each position in the scanned area by an electron detector. The intensity of the emitted electron signal is displayed as brightness on a display monitor, (Materials Evaluation and Engineering, Inc., 2018).
TEM
Transmission electron microscopy is a microscopy technique in which a beam of electrons is transmitted through a sample and an image is produced for analysis. A typical TEM in a laboratory contains 7 components: Electron Column, Magnetic Lens System, Detectors, Electron Gun, Sample Chamber, Main Control Panel and Operational controls and Image Capture
The images allow researchers to view samples on a molecular level, making it possible to analyze structure and texture.
Technology companies use TEMs to identify flaws, fractures and damages to micro-sized objects; this data can help fix problems and/or help to make a more durable, efficient product.
Advantages of TEM
TEMs offer the most powerful magnification, potentially over one million times or more
TEMs have a wide-range of applications and can be utilized in a variety of different scientific, educational and industrial fields
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TEMs are able to yield information of surface features, shape, size and structure
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EDXA
Energy Dispersive X-Ray Analysis (EDX is an x-ray technique used to identify the elemental composition of materials. Applications include materials and product research.
EDX systems are attachments for SEM’s or TEM’s instruments where the imaging capability of the microscope identifies the specimen of interest. The EDX analysis generates spectra showing peaks corresponding to the elements composing the sample being analysed. Elemental mapping of a sample and image analysis are also possible.
The technique can be qualitative, semi-quantitative, quantitative and also provide spatial distribution of elements through mapping. The EDX technique is non-destructive and specimens of interest can be examined in situ with little or no sample preparation.
In situations where combined Microscopy and EDX data acquired are insufficient to identify a specimen, complementary techniques are available, typically Infra-red (FTIR) Microscopy, RAMAN Microscopy, Nuclear Magnetic Resonance Spectroscopy (NMR) and Surface Analysis (X-ray photoelectron spectroscopy (XPS) or Time-of-Flight Secondary Ion Mass Spectrometry (SIMS)).
EDX relies on an interaction of X-ray excitation and a sample. Its characterization capabilities are due in large part to the fundamental principle that each element has a unique atomic structure allowing a unique set of peaks on its electromagnetic emission spectrum
Energy Dispersive X-ray Spectroscopy is based on the detection of characteristic x-rays emitted of an element as a result of the de-excitation of core electron holes created by a high energy electron beam. An electron from a higher binding energy electron level falls into the core hole and an x-ray with the energy of the difference of the electron level binding energies is emitted. The number and energy of the X-rays emitted from a specimen can be measured by an energy-dispersive spectrometer. As the energies of the X-rays are characteristic of the difference in energy between the two shells and of the atomic structure of the emitting element, EDS allows the elemental composition of the specimen to be measured.
WDXA
Wave Dispersive X-Ray analysis
- counts the number of x-rays of a specific wavelength that are diffracted by a crystal
- the crystal, specimen and detector are mounted, with equal distance between each, to allow the measurement of the angle of diffraction of the x-rays
X-rays given off by elements are characteristic. The technique is used to gain elemental composition of a sample. It is typically used in conjunction with SEM.
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