Collision cascades

Fig. 1. The ballistic interactions of an energetic ion with a sohd. Depicted are sputtering events at the surface, single-ion /single-atom recoil events, the development of a collision cascade involving a large number of displaced atoms, and the final position of the incident ion. ° = normal atom ...

By 1969, when a major survey (Thompson 1969) was published, the behaviour of point defeets and also of dislocations in crystals subject to collisions with neutrons and to the eonsequential collision cascades had become a major field of researeh. Another decade later, the subjeet had developed a good deal further and a highly quantitative body of theory, as well as of phenomenological knowledge, had been assembled. Gittus (1978) published an all-embracing text that eovered a number of new topics chapter headings include Bubbles , Voids and Irradi-ation(-enhanced) Creep . 

Todorov et al. [73] made equivalent assumptions in the modeling of a-CN.v film growth within another context. They focused their attention on the calculation of the collision cascade details following subsurface penetration of and N+ ions... 

Fig. 12. Collision cascades induced by a recoil-implanted atom with the generation of heat and pressure pulses [56]...

SIMS involves bombarding a material surface with a primary ion beam, with a typical energy in the keV range. Ion impacts on the surface induce a so-called collision cascade sputtering process, where the energy of the primary ions is transferred to the surface through nuclear collisions [Brunelle et al. 2005]. 

Figure 15.1 Collision cascade and secondary ion production during ToF SIMS analysis...

When a surface is exposed to a beam of ions, energy is deposited in the surface region of the sample by a collision cascade. Some of the energy will return to the... 

The angular dependence of the secondary ion intensity is expected to follow a simple cosine law, in particular for randomly oriented polycrystalline surfaces. The explanation for this is that upon impact the collision cascade takes care of an isotropic distribution of the energy through the sample. Hence the intensity of collision... 

Fig. 9.4. Simple illustration of an instantaneous collision cascade generated as a result of primary particle impact in desorption/ionization mass spectrometry. Adapted from Ref. [24] by permission. John Wiley Sons, 1995.

Figure 1. Principles of plasma interaction with material. The Ar ions hit polymer surface and create a collision cascade in the surface layer by which a number of atoms are set in movement. As a result ionization of atoms and molecular bond cleavage take place and some of liberated atoms are ejected (sputtering process) [6].

TAD has been demonstrated to be very effective for studying the long-time behavior of defects produced in collision cascades [25,26]. An MD/TAD procedure has also been applied to the simulation of thin-film growth of Ag... 

Collision cascades (see Fig. 1) lead to a distribution of vacancies, interstitial atoms, and other types of lattice disorder in the region around the ion... 

Thus as a starting point for understanding the bombardment process we have developed a classical dynamics procedure to model the motion of atomic nuclei. The predictions of the classical model for the observables can be compared to the data from sputtering, spectrometry (SIMS), fast atom bombardment mass spectrometry (FABMS), and plasma desorption mass spectrometry (PDMS) experiments. In the circumstances where there is favorable agreement between the results from the classical model and experimental data It can be concluded that collision cascades are Important. The classical model then can be used to look at the microscopic processes which are not accessible from experiments In order to give us further insight into the ejection mechanisms. 

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