Electron interaction with matter

Electron dynamic scattering must be considered for the interpretation of experimental diffraction intensities because of the strong electron interaction with matter for a crystal of more than 10 nm thick. For a perfect crystal with a relatively small unit cell, the Bloch wave method is the preferred way to calculate dynamic electron diffraction intensities and exit-wave functions because of its flexibility and accuracy. The multi-slice method or other similar methods are best in case of diffraction from crystals containing defects. A recent description of the multislice method can be found in [8]. 

The future for electron diffraction is very bright for two reasons. First, electron diffraction pattern can be reeorded seleetively from individual nanostrueture at sizes as small as a nanometer using the electron probe forming lenses and apertures, while eleetron imaging provides the selectivity. Second, electrons interact with matter mueh more strongly than X-ray and Neutron diffraction. These advantages, eoupled with quantitative analysis, enable the structure determination of small, nonperiodic, structures that was not possible before. 

When electrons interact with matter, they lose energy by four mechanisms... 

A companion field, Auger electron spectroscopy (AES), was developed simultaneously. AES does not provide chemical species information, only elemental analysis, as we will see. Since the electrons ejected in these two techniques are of low energy and the probability of electron interaction with matter is very high, the electrons cannot escape from any significant depth in the sample. Typical escape depths for XPS and AES electrons range from 0.5 to 5 nm for materials. The phenomenon is therefore confined to a few atomic layers, combined or otherwise, which are at the surface of the sample and provides a method of surface analysis. 

As a high energy radiation particle such as an electron interacts with matter, it loses its energy to the liquid water generating a track of events along its passage... 

In addition to Compton scattering, y-rays having energies above 1022 keV interact with matter by a process called pair production, in which the photon is converted into a positron and an electron. The y-ray energy in excess of the 1022 keV needed to create the pair is shared between the two new particles as kinetic energy. Each j3 -particle is then slowed down and annihilated by an electron producing two 511-keV photons. 

For 7-ray energies below 1 MeV (the range of interest) there are two principal modes of interaction with matter — Compton scattering and photoelectron absorption. Compton scattering is the elastic scattering of the 7 photon by an orbital electron in which part of the incident 7-energy is imparted to the recoiling electron. 

X-rays are electromagnetic radiation with short wavelengths of about 0.01 to 10 nm. X 0.15 nm is the typical wavelength for the study of soft condensed matter. Whenever X-rays are interacting with matter, their main partners are the electrons in the studied sample. Thus X-ray scattering is probing the distribution of electron density, p (r), inside the material. 

This book lays emphasis on the fundamental aspects of the chemical consequences of charged particle interactions with matter, particularly in the condensed phase. No details will be given about experimental apparatus or procedure, but results of experiments are discussed in relation to theoretical models. The role of the electron both as a radiation (primary and secondary) and as a reactant has been fully treated. Wherever necessary, physical theories have been discussed in detail with understanding of radiation-chemical experiments in view. 

All analytical methods that use some part of the electromagnetic spectrum have evolved into many highly specialized ways of extracting information. The interaction of X-rays with matter represents an excellent example of this diversity. In addition to straightforward X-ray absorption, diffraction, and fluorescence, there is a whole host of other techniques that are either directly X-ray-related or come about as a secondary result of X-ray interaction with matter, such as X-ray photoemission spectroscopy (XPS), surface-extended X-ray absorption fine structure (SEXAFS) spectroscopy, Auger electron spectroscopy (AES), and time-resolved X-ray diffraction techniques, to name only a few [1,2]. 

The convenience of using X-rays for stmcture determination stems from the nature of their interactions with matter the wavelengths of radiation in the X-ray region of the electromagnetic spectmm are comparable to the sizes of atoms and interatomic distances that are to be analyzed. Although, in principle, interatomic distances can be determined by electron microscopy, unlike electron microscopic... 

Ionizing radiation, as the term implies, defines those radiations that interact with matter by the production of charged particles, namely electrons and residual positive ions. 

Clearly, UV and EB radiation have a great deal in common, as shown above. However, there are also differences. Besides the nature of interacting with matter, where high-energy electrons penetrate, and photons cause only surface effects, there are issues concerning the capital investment and chemistry involved. 

Electron beam processors generate two types of ionizing radiation their primary product is high-energy electrons, and their secondary product is x-rays resulting from their interaction with matter. The ionizing radiation is damaging because of its capability of penetration into the human body. 

When radiation of sufficiently short wavelength interacts with matter, ( electrons are emitted. This is the photoelectric effect. It can be observed in gases and solids, and with X-rays and y rays, as well as with ultraviolet j radiation. It was die phenomena observed with short-wavelength visible and < ultraviolet radiation on solids, however, which were known in 1905. Figure J 1.10 shows the apparatus used. Light or UV radiation falls on one electrode 4 in an evacuated tube. If electrons are emitted, some will reach the second <... 

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