Bombardment-induced kinetics

It is important to note that Eqs. 5, 8, and 9 were derived entirely from a silicon material balance and the assumption that physical sputtering is the only silicon loss mechanism thus these equations are independent of the kinetic assumptions incorporated into Eqs. 1, 2, and 7. This is an important point because several of these kinetic assumptions are questionable for example, Eq. 2 assumes a radical dominated mechanism for X= 0, but bombardment-induced processes may dominate for small oxide thickness. Moreover, ballistic transport is not included in Eq. 1, but this may be the dominant transport mechanism through the first 40 A of oxide. Finally, the first 40 A of oxide may be annealed by the bombarding ions, so the diffusion coefficient may not be a constant throughout the oxide layer. In spite of these objections, Eq. 2 is a three parameter kinetic model (k, Cs, and D), and it should not be rejected until clear experimental evidence shows that a more complex kinetic scheme is required. 

Neutrons readily induce nuclear reactions, but they always produce nuclides on the high neutron-proton side of the belt of stability. Protons must be added to the nucleus to produce an unstable nuclide with a low neutron-proton ratio. Because protons have positive charges, this means that the bombarding particle must have a positive charge. Nuclear reactions with positively charged particles require projectile particles that possess enough kinetic energy to overcome the electrical repulsion between two positive particles. 

For small kinetic energies, most of the secondary electrons are generated as consequence of the potential energy of the impinging ion (potential ejection) however, kinetic ejection becomes dominant as the kinetic energy is increased. The difference between potential and kinetic ejection is clearly established by the data of Medved et al. (see Fig. 8), who compared the yield of secondary electrons from molybdenum induced by Ar bombardment (potential plus kinetic ejection) with the yield obtained under bombardment by neutral argon atoms of... 

The first example of the application of atomistic simulation to a materi-als-related area is probably the work of Vineyard and co-workers. They used classical trajectories to model damage induced in a solid by bombardment with ions having hyperthermal kinetic energies. These calculations, which were done at about the same time as Rahman s initial studies on liquids, provided important data related to damage depth as well as new insights into many-body collisions in solids. The potentials used were continuous pair-additive interactions similar to those employed in Rahman s simulations. 

NUCLEAR TRANSMUTATIONS (SECTION 21.3) Nuclear transmutations, induced conversions of one nucleus into another, can be brought about by bombarding nuclei with either charged particles or neutrons. Particle accelerators increase the kinetic energies of positively charged particles, allowing these particles to overcome their electrostatic repulsion by the nucleus. Nuclear transmutations are used to produce the transuranium elements, those elements with atomic numbers greater than that of uranium. 

Most nuclides with mass numbers between 225 and 250 do not undergo fission spontaneously (except for a few with extremely long half-lives). They can be induced to undergo fission when bombarded with particles of relatively low kinetic energies. Particles that can supply the required activation energy include neutrons, protons, alpha particles, and fast electrons. For nuclei lighter than mass 225, the activation energy required to induce fission rises very rapidly. 

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