Transmission secondary electron

Transmission secondary electron (TSE) devices made from InGaP/GaAs structures which exhibit gains as high as 540 at primary energies of 20 kV. 

In transmission electron microscopy (TEM), a beam of highly focused and highly energetic electrons is directed toward a thin sample (< 200 nm) which might be prepared from solution as thin film (often cast on water) or by cryocutting of a solid sample. The incident electrons interact with the atoms in the sample, producing characteristic radiation. Information is obtained from both deflected and nondeflected transmitted electrons, backscattered and secondary electrons, and emitted photons. 

The surface sensitivity is ensured by detecting the decay products of the photoabsorption process instead of the direct optical response of the medium (transmission, reflection). In particular one can measure the photoelectrons, Au r electrons, secondary electrons, fluorescence photons, photodesorbed ions and neutrals which are ejected as a consequence of the relaxation of the system after the photoionization event. No matter which detection mode is chosen, the observable of the experiment is the interference processes of the primary photoelectron with the backscattered amplitude. 

The most recent calculations, however, of the photoemission final state multiplet intensity for the 5 f initial state show also an intensity distribution different from the measured one. This may be partially corrected by accounting for the spectrometer transmission and the varying energy resolution of 0.12, 0.17, 0.17 and 1,3 eV for 21.2, 40.8, 48.4, and 1253.6 eV excitation. However, the UPS spectra are additionally distorted by a much stronger contribution of secondary electrons and the 5 f emission is superimposed upon the (6d7s) conduction electron density of states, background intensity of which was not considered in the calculated spectrum In the calculations, furthermore, in order to account for the excitation of electron-hole pairs, and in order to simulate instrumental resolution, the multiplet lines were broadened by a convolution with Doniach-Sunjic line shapes (for the first effect) and Gaussian profiles (for the second effect). The same parameters as in the case of the calculations for lanthanide metals were used for the asymmetry and the halfwidths ... 

To decide whether a surface effect is present and, if so which, the experimental spectra shown in Fig. 16 have been corrected for the spectrometer transmission. The secondary electron contribution and the emission from conduction band states have also been subtracted. Comparing this spectrum with calculated multiplet intensities it seems that a contribution from a divalent Am surface resulting in a broad structureless 5f 5f line at 1.8 eV is the most suitable explanation of the measured intensity distribution. Theory also supports this interpretation, since the empty 5f level of bulk Am lies only 0.7 eV above Ep within the unoccupied part of the 6d conduction band (as calculated from the difference of the Coulomb energy Uh and the 5 f -> 5 f excitation energy Any perturbation inducing an increase of Ep by that amount will... 

Figure 7. Scanning transmission scanning electron micrograph of a test pattern developed in a 30 nm thick layer of PMMA. Pattern was written with an electron beam with a diameter below 1 nm. The narrowest lines are 10 nm wide. Minimum linewidth and center-to-center spacing is limited by straggling of secondary electrons into the resist.

This type of electron microscope is completely different in principle and application from the conventional transmission-type electron microscope. In the scanning instrument, the surface of a solid sample is bombarded with a fine probe of electrons, generally less than 100 A in diameter. The sample emits secondary electrons that are generated by the action of the primary beam. These secondary electrons are collected and amplified by the instrument. Since the beam strikes only one point on the sample at a lime, the beam must be scanned over the sample surface in a raster pattern to generate a picture of the surface sample. The picture is displayed on a cathode ray tube from which it can be photographed. 

The electron microscope has a resolution of 10 3-10 4 p. A well-known example of an electron microscope is the TEM, the transmission electron microscope, which is used to study specimens a fraction of a micrometre or less in thickness, e g. for depicting and recognizing clay minerals. Another type of electron microscope is used to depict surfaces and is often applied for ceramics. The surface of a slide is radiated with a beam of electrons. Some electrons are bounced back and due to the collisions of fast electrons secondary electrons are liberated from the surface. In this way you can obtain more information about the surface relief and the chemical composi-tion. The SEM, the scanning electron microscope radiates a surface with a controlled electron beam. In this way a certain part of the surface can be studied. 

SEM is particularly useful for showing up the surface structure of materials by analysing the secondary electrons. Transmission electron microscopy (TEM) relies on the use of the electrons passing through the very thin samples and can show up images of the internal structure of samples. It can achieve a resolution of about 1 x 10-10 m. Both SEM and TEM require a high vacuum and so samples must be stable in vacuums and when subjected to fast moving electrons. 

The surface morphology of grains has been studied by secondary electron microscopy (SEM) (Hoppe et al., 1995). Such studies have been especially useful for pristine SiC grains that have not been subjected to any chemical treatment (Bernatowicz et al., 2003). Finally, the transmission electron microscope (TEM) played an important role in the discovery of presolar SiC (Bernatowicz et al., 1987) and internal TiC and other subgrains in graphite (Bernatowicz et al., 1991). It has also been successfully applied to the study of diamonds (Daulton et al., 1996) and of polytypes of SiC (Daulton et al., 2002, 2003). 

In secondary electron microscopy (SEM), in most cases, SEs are used for imaging. BSE detectors are closely connected with element analysis of the specimen. Other types are more or less seldom used in electron microscopy. In transmission electron microscopy (TEM), TEs will be processed to give an image. 

The scanning electron microscope is based on a somewhat different principle than the transmission electron microscope. In the scanning electron microscope, the viewed image is formed by the secondary electrons emitted from the sample surface when an electron beam is scanned across this surface. These secondary electrons are detected by a suitable detector and counted. An image is then formed on a cathode ray tube in which the brightness of the raster spot is proportional to the number of electrons emitted at each point on the sample surface. In order to prevent charging of the surface as the electron beam is scanned across it, the surface is coated with a conductor such as gold. 

AH - EPR signal linewidth AT/T - relative change in transmission D - electron donor, or secondary electron donor D - alternative designation for the primary electron donor cf. P ... 

With modern scanning electron microscopes many of the restrictions of the transmission electron microscope have been alleviated. Firstly, thin samples are no longer required. With instruments equipped with a field-emission gun, magnifications as low as 50X and as high as lOOOOOX can be achieved routinely. Imaging the back-scattered electrons gives the distribution of the heavy elements at a high resolution, whereas the secondary electrons are indicative of the shape and the size of the solid particles present in the specimen. Analysis of the emitted X-rays can indicate the elemental composition. 

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