Interaction of Electrons with Matter

HIGH RESOLUTION ANALYTICAL ELECTRON MICROSCOPY (HRAEM) 5.1.1 Interaction of Electrons with Matter 

The terms elastic and inelastic scattering of electrons describe that which results in no loss of energy and some measureable loss of energy respectively. If the incident electron beam is coherent (i.e. the electrons are in phase) and of a fixed wavelength, then elastically scattered electrons remain coherent and inelastic electrons are usually incoherent. 

There are three types of electron microscopes commonly used for microanalysis. These are the scanning electron microscope (SEM) with X-ray detectors, the electron probe microanalyser (EPMA), which is essentially a purpose built analytical microscope of the SEM type, and transmission microscopes (TEM and STEM) fitted with X-ray detectors. In a TEM, compositional information may also be obtained by 

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B1.17.2 INTERACTION OF ELECTRONS WITH MATTER AND IMAGING OF THE SCATTERING DISTRIBUTION... 

The continuous spectrum is thus characterized by a short-wavelength limit and an intensity distribution. Experiments on other target materials have shown that these characteristics are independent of the target material although the integrated intensity increases with atomic number. (See Equation 1-3.) The continuous spectrum, therefore, results generally from the interaction of electrons with matter. Attempts (none completely successful) have been made to treat this interaction theoretically by both classical and quantum mechanics. 

The interaction of electrons with matter is similar to the interaction of heavy particles, with the following differences ... 

The following interactions of electrons with matter can be visualized... 

The interaction of electrons with matter generates X-rays. In Electron probe microanalysis (EPMA), these are analysed to yield information about the elemental composition of the specimen. 

The interaction of electrons with matter is different from that of heavier charged particles for two reasons. One of them is the electron mass which is more than two orders of magnitude lower than that of the second lightest charged particle, the muon this makes photon radiation very important in the stopping power of electrons even at lower energies. The other reason is that at low energies, the interaction with shell electrons dominates and that is collision between identical particles, which has to be taken into account in the calculations. 

In this review we consider how EELS complements other high-energy spectroscopies in elucidating the electronic properties of rare earths and their compounds. Section 2 reviews the interaction of electrons with matter, while section 3 surveys the experimental techniques of transmission and reflection EELS. Section 4 considers excitation of the outer electrons in rare earth metals and their compounds one-electron and plasmon losses show both continuation of bulk properties to the surface and modified surface environment. Section 5 looks at core excitations, which emphasise atomic rather than band-like properties, while section 6 suggests new applications of EELS which will enhance understanding of the idiosyncracies of rare earth systems that keep the rare earth community both intrigued and employed. 

Figure 8.1 Schematic representation of the interaction of electrons with matter and the signals generated.

Conventional electron microscopes operate under high vacuum. This is because of the strong interaction of electrons with matter. Any gas molecules in the path of the incident beam will scatter and diffuse the electrons, at best lowering the resolution of the image. In order to place a sample in... 

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