Scanning beam-specimen secondary electrons

Scanning electron microscopy (SEM) seems to have been used only scarcely for the characterization of solid lipid-based nanoparticles [104], This method, however, is routinely applied for the morphological investigation of solid hpid microparticles (e.g., to smdy their shape and surface structure also with respect to alterations in contact with release media) [24,38,39,41,42,80,105]. For investigation, the microparticles are usually dried, and their surface has to be coated with a conductive layer, commonly by sputtering with gold. Unlike TEM, in SEM the specimen is scanned point by point with the electron beam, and secondary electrons that are emitted by the sample surface on irradiation with the electron beam are detected. In this way, a three-dimensional impression of the structures in the sample, or of their surface, respectively, is obtained. 

In this type of Microscopy a fine beam of electrons is scanned across the surface of an opaque specimen to which a light conducting film has been applied by evaporation. Secondary electrons, backscattered elections, or (in the electron microprobe)... 

In scanning electron microscopy (SEM), a finely focussed electron beam probe moves from one point on the specimen to the next to form a raster pattern, just as in television imaging. The intensity of scattered or secondary electrons is continuously... 

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. 

In scanning electron microscopy, the surface of a whole specimen is coated with a layer of heavy metal and then scanned with an electron beam. Excited molecules in the specimen release secondary electrons which are focused to produce a three-dimensional image of the specimen. 

SEs and BSEs are typically detected by an Everhart-Thornley (ET) scintillator-photomultiplier secondary electron detector. The SEM image is shaped on a cathode ray tube screen, whose electron beam is scanned synchronously with the high-energy electron beam, so that an image of the surface of the specimen is formed [52], The quality of this SEM image is directly related to the intensity of the secondary and/or BSE emission detected at each x- and y-point throughout the scanning of the electron beam across the surface of the material [8],... 

This technique is used to study the surface or near-surface characteristics of specimens, and is one of the most versatile and widely used instruments in science. In this technique, a beam of electrons from a thermionic emission type tungsten filament is accelerated to 20-40 KeV, demagnified and reduced in diameter to 2-10nm on point of contact with a sample. The fine beam is scanned across the sample and a detector counts the number of low-energy secondary electrons or the radiation given off from each point on the surface (McHardy and Bimie, 1987 Newbury et al., 1987 Goodhew and Humphreys, 1988). Electron emission from a... 

The surface structure of thicker samples can be examined using scanning electron microscopy (SEM). Here a fine beam of electrons is scanned across the surface of the specimen, and the scattered secondary electrons emitted from the surface of the sample are detected electronically. Secondary electrons are best produced by electron collision with conduction electrons in a metal surface (by analogy with the photoelectric effect), so samples for SEM are usually coated by evaporation with a thin film of gold in order to make them more visible. This naturally limits the fine detail that can be seen. 

Iron microscope can be used with thicker specimens and forms a perspective im e, although the resolution and m nification are lower. In this type of instrument a beam of primary electrons scans the specimen and those that are reflected, together with any secondary electrons emitted, are collected. This current Is used to modulate a separate electron beam in a TV monitor, which scans the screen at the same frequency, consequently building up a picture of the specimen. The resolution is limited to about 10-20 nm. See also field-emission microscope EIELD-IONIZATION MICROSCOPE. 

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