With the support of ray, diagrams explain how the images were obtained. Your explanation must include comments about the location and use of the objective and selected area apertures. A TEM consists of condenser lenses to focus the electron beam on the specimen, an objective lens to form diffraction in the BFP (Back focal plane) and the image in the image plane, and other lenses to magnify the image or the diffraction pattern on the screen. In order to obtain images in TEM, we either focus on the central spot (direct beam), or on the scattered electrons (diffracted beam). This is done by inserting an aperture (selected area aperture) into the BFP of the objective lens followed by selecting the appropriate beam. Bright field image (Figure 1) The given micrograph depicts a dark MgO crystal on a light and bright background. The topography on the face of the crystal is very clear. Such an image is called a bright field image and has a very high contrast. ...
The parts of the crystal in Bragg orientation appear dark, and the amorphous parts of the crystal are bright. The objective diaphragm is adjusted in such a way that an aperture appears in the back focal plane of the objective lens, allowing only the direct beam to enter and blocking the diffracted beam. The objective aperture, when inserted, controls the collection angle. The placement of the SAD (selected area aperture) is critical as it should be adjusted to obtain only the direct beam in this case. Darkfield image (Figure 2) The micrograph in figure two depicts a bright MgO crystal on a dark background. Such an image is obtained by selecting only the scattered electrons using a selected area aperture, enabling them to reach the image plane. The electrons that are not in the direct beam are selected to form a dark field image. The objective aperture is moved sideways to select the un-scattered electrons. This method is of high utility in case of observing certain specific crystallographic orientations of the specimen. The dark field image can also be obtained through another method, called centered dark field operation. In this case, the objective aperture is not shifted and the primary/direct beam is used instead. "The beam is tilted in order to allow only the scattered/diffracted electrons to go through the objective aperture (William and Carter 2009). Selected area diffraction pattern SAED (Figure 7) The given micrograph clearly depicts the symmetry of the lattice of MgO crystal through a selected area diffraction pattern. Selected area diffraction patterns are obtained by inserting the SAD aperture into the image plane of the objective lens and aperture on the optic axis in the middle of the viewing screen (William and Carter 2009).
This essay analyzes Transmission Electron Microscopy, that has revolutionized the field of microscopy, touching a variety of aspects, both biological and physical. TEMs comprise a range of different instruments that make use of the properties of electrons, both as particles and as waves…
The paper gives detailed information about the TEM, that generates a tremendous range of signals so we can obtain images, DPs and several different kinds of spectra from the same small region of the specimen (Williams and Carter 2009). A TEM consists of condenser lenses, an objective lens and the image in the image plane.
The above micrographs represent a Secondary electron image (SE) and a Backscatter electron image (BSE) of the same region of an asbestos sample.The SE image appears more three dimensional than the BSE image. The cluster of fibers at the center in the SE image appears more rounded, while the one in the BSE appears flat.
Images in TEM are obtained by focusing an electron beam on the specimen. The electrons are absorbed, transmitted, scattered or backscattered. Depending on the kind of image required by the operator, either the transmitted electrons (called direct beam) or the scattered electrons (called diffracted beam) is selected.
From this paper, it is clear that TEM has a large number of applications in innumerable fields ranging from life sciences to material science. TEM has proved to be a priceless tool for studying the ultrastructure of metals (Egerton 2005, 14). In life sciences, it is used for studying bacteria, viruses, and tissues of plants and animals.
SEM images were used to carry out size distribution analysis of the powder particles using a software package CARNOY. BSE image of the powder particles was taken and EDS was performed to get chemical information about bright particles in the powder sample.
Different attributes of particles like particle shape, size and size distribution and chemical composition of different particles were determined. SEM analysis shows that there is multimodal distribution of particle size with modes at 25 ?m, 60 ?m and 115 ?
This essay analyzes that spherical aberration also occurs in the Electron Microscopes when electrons passing through the side of the lens are refracted greater than those passing along the axis.2 (Lam, 2009); while Diffractive aberrations are brought about by the deviations from geometrical optics caused by the wave nature of light.
From this paper it is clear that to obtain such a pattern, the selected area aperture is placed in the image plane of the objective lens and used to select only one part of the image. Using projector lenses to focus on electron beams to obtain small spots on the object surface, the diffraction patterns can be obtained.
This essay analyzes that in an electron microscope, the electrons are accelerated in a vacuum until their wavelength is shortened. Shorter wavelengths can be produced by increasing the voltage. Beams of these fast-moving electrons are focused on an object. The object either absorbs these beams and forms an image on an electron-sensitive photographic plate.
Besides, attenuation of the primary electron beam will also be lesser. This will lead to better image quality and better microanalytical capability of a TEM. Besides, minimizing molecule – electron beam interaction, better vacuum level
3 pages (750 words)Coursework
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