Collision sputtering

Figure 8.2 The sputtering process in SIMS (a) direct collision sputtering (b) collision cascade and (c) thermal sputtering. (Reproduced with kind permission of Springer Science and Business Media from R. Behrisch, Ed., Sputtering by Particle Bombardment I, Springer-Verlag Gmbh, Berlin. 1981 Springer Science.)...

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 ...

Figure 1 Schematic of DC glow-discharge atomization and ionization processes. The sample is the cathode for a DC discharge in 1 Torr Ar. Ions accelerated across the cathode dark space onto the sample sputter surface atoms into the plasma (a). Atoms are ionized in collisions with metastable plasma atoms and with energetic plasma electrons. Atoms sputtered from the sample (cathode) diffuse through the plasma (b). Atoms ionized in the region of the cell exit aperture and passing through are taken into the mass spectrometer for analysis. The largest fraction condenses on the discharge cell (anode) wall.

In secondary ion mass spectrometry (SIMS), a beam of energetic primary ions is focused onto the surface of a solid. Some of the ions are reflected but most of the energy of the primary ions is dissipated in the surface by binary collisions that cause neutrals, excited neutrals, and ions (positive and negative) to be ejected or sputtered from the surface. The secondary ions can be analyzed by a mass spectrometer to provide information about the surface composition of the solid. 

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]. 

Energy Increasing the energy of the primary ions initially increases the sputter yield. At high energy, however, ions penetrate deeper into the solid and dissipate their energy further away from the surface. The result is that fewer collision cas-... 

Figure 4.19 The LEIS spectrum of a Cu/Al203 catalyst illustrates that ions lose more energy in collisions with light elements than with heavy elements. Note the step in the background at the low kinetic energy side of the peaks. The high peak at low energy is due to sputtered ions. The low energy cut-off of about 40 eV is indicative of a positively charged sample (courtesy of J.P. Jacobs and H.H. Bron-gersma, Eindhoven).

The primary ion impact is believed to start a cascade of collisions between the impacting particle and the atomic nucleii in the sample, resulting in ejection of neutral molecules and ions through so-called sputtering (Fig. 2.8) [119]. The SIMS... 

P. Sigmund and C. Claussen. Sputtering from Elastic-Collision Spikes in Heavy-Ion-Bombarded Metals. J. Appl. Phys., 52(1981) 990-993. 

Synthesis of nano-structured alloys by the inert gas evaporation technique A precursor material, either a single metal or a compound, is evaporated at low temperature, producing atom clusters through homogeneous condensation via collisions with gas atoms in the proximity of a cold collection surface. To avoid cluster coalescence, the clusters are removed from the deposition region by natural gas convection or forced gas flow. A similar technique is sputtering (ejection of atoms or clusters by an accelerated focused beam of an inert gas, see 6.9.3). 

Molecular dynamics simulations have yielded a great deal of information about the sputtering process. First, they have demonstrated that for primary ion energies of a few keV or less, the dynamics which lead to ejection occur on a very short timescale on the order of a few hundred femtoseconds. This timescale means that the ejection process is best described as a small number of direct collisions, and rules out models which rely on many collisions, atomic vibrations and other processes to reach any type of steady state . Within this same short-timescale picture, simulations have shown that ejected substrate atoms come from very near the surface, and not from subsurface regions. 

Magnera, T.F. David, D.E. Stulik, D. Orth, R.G. Jonkman, H.T. Michl, J. Production of Hydrated Metal Ions by Fast Ion or Atom Beam Sputtering. Collision-Induced Dissociation and Successive Hydration Energies of Gaseous Cu With 1-4 Water Molecules. J. Am. Chem. Soc. 1989, 111, 5036-5043. 

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].

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