Secondary electrons types

Detecting ions in GC/MS is performed almost exclusively using an electron multiplier. There are two types of electron multipliers the continuous dynode type and the discrete type. Both operate on the principle that ions with sufficient kinetic energy will emit secondary electrons when they strike a metal surface. The discrete type of electron multiplier has a series of... 

The secondary electrons emitted from the sample are collected in the sample chamber. The most common type of secondary electron detector is the scintilla-... 

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)... 

Figure 12.20 shows the structure of the side-window circular cage type and linear focused head-on type of photomultiplier which are both preeminent in fluorescence studies. The lower cost of side-window tubes tends to favor their use for steady-state studies, whereas the ultimate performance for lifetime studies is probably at present provided by linear focused devices. In both types internal current amplification is achieved by virtue of secondary electron emission from discrete dynode stages, usually constructed of copper-beryllium (CuBe) alloy, though gallium-phosphide (GaP) first dynodes have been used to obtain higher gains. 

Track structure simulation has found application in many areas of radiation research since the pioneering studies of Mozumder and Magee [35]. These studies all employ essentially the same type of approach, a collision-to-collision modeling of the trajectory of the primary radiation particle and of its daughter secondary electrons, with the most significant difference between different calculations being the interaction cross sections used to describe the... 

Secondary-electron coefficients are strongly dependent upon the condition of the surface. The presence of adsorbed gas or surface roughness can significantly alter the number of secondary electrons. Moreover, much of the work in this field predates ultra-high-vacuum technology and the associated surface-characterization tools (for reviews see Refs. 144-146). In addition, surfaces exposed to a plasma are not well characterized. Therefore, crude, estimates of the magnitude of the secondary-electron coefficients seem to be the most useful type of data in the present context. 

Figure 2.4 Different types of interactions of electrons with a solid 1, X-ray or optical photons 2, back-scattered electrons 3, secondary electrons 4, coherent elastic scattering 5, inelastic scattering 6, incoherent elastic scattering.

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. 

A block diagram of a scanning-type electron microscope is given in Fig. 5. Major elements of the instrument include the electromagnetic lenses that are used to form the electron probe, the scan coils that sweep the beam over the sample, the detector that collects the secondary electrons, and the amplifying means where the secondary electrons are amplified and fed to the cathode ray tube for display. Since the cathode ray tube is scanned in synchronization with the electron beam, the resulting picture corresponds to the area of the sample being examined. 

The multiplier structures may be divided into two main types (1) dynamic and (2) static. The dynamic multiplier in its simplest form consists of two parallel dynode surfaces with an alternating electric field applied between them. Elections leaving one suiface at the piopei phase, of the applied field are accelerated to the other surface where they knock out secondary electrons. These electrons, in turn, are accelerated back to the first plate when the field reverses, creating still more secondary electrons. Eventually, the secondary electrons are collected by an anode placed in... 

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