Energy of bombardment

Since the main parameter influencing diamond-like carbon film structure is the energy of bombarding ions, it is expected that the same happens with a-C H films. In fact, it was found that in RFPECVD deposition of a-C H films, the variation of substrate self-bias results in strong changes of film growth, composition, structure, and properties. 

Fig. 16.4. Experimental and predicted atomic N/C ratios as a function of kinetic energy of bombarding ions.

For a given energy of bombardment all these reactions tend to take place to a certain extent. At low energies the (d,w) reaction frequently predominates, while the (d,p), (d, ), (d,t), and (d,2n.) reactions become increasingly important as the deuteron energy is increased. This complexity compares unfavorably with thermal-neutron activation where frequently one reaction occurs to the virtual exclusion of all others. 

Figure 2-18. Secondary electron emission as a function of energy of bombarding electrons.

Figure 24.7 shows dependences of a microhardness value on the energy of bombarding ions these dependences were used by the IBAD method and were taken from the papers [13,16-18]. Lower microhardness values were obtained in the paper [17], in which high densities of ion flows of 100-200 pA/cm were used and as a result a coating structure corresponded to the Cr + Cr2N... 

Vitkavage D J, Dale C J, Chu W K, Finstad T G and Mayer T M 1986 Ion channeling studies of low energy ion bombardment induced crystal damage in silicon Nucl. Instrum. Methods B 13 313-18... 

Radiation Damage. It has been known for many years that bombardment of a crystal with energetic (keV to MeV) heavy ions produces regions of lattice disorder. An implanted ion entering a soHd with an initial kinetic energy of 100 keV comes to rest in the time scale of about 10 due to both electronic and nuclear coUisions. As an ion slows down and comes to rest in a crystal, it makes a number of coUisions with the lattice atoms. In these coUisions, sufficient energy may be transferred from the ion to displace an atom from its lattice site. Lattice atoms which are displaced by an incident ion are caUed primary knock-on atoms (PKA). A PKA can in turn displace other atoms, secondary knock-ons, etc. This process creates a cascade of atomic coUisions and is coUectively referred to as the coUision, or displacement, cascade. The disorder can be directiy observed by techniques sensitive to lattice stmcture, such as electron-transmission microscopy, MeV-particle channeling, and electron diffraction. 

The origin of the sputtered atoms may result from displacement below the surface of the source, a so-called thermal spike, as well as dhectly from the surface, depending on the incident energy of tire bombarding ions, ,. This must reach a tlrreshold value, before any atoms are dislodged from the target and... 

It is a fundamental principle of quantum mechanics that electrons bound in an atom can have only discrete energy values. Thus, when an electron strikes an atom its electrons can absorb energy from the incident electron in specific, discrete amounts. As a result the scattered incident electron can lose energy only in specific amounts. In EELS an incident electron beam of energy Eq bombards an atom or collection of atoms. After the interaction the energy loss E of the scattered electron beam is measured. Since the electronic energy states of different elements, and of a single element in different chemical environments, are unique, the emitted beam will contain information about the composition and chemistry of the specimen. 

Other considerations are that the source material, which forms a target for high-energy electron bombardment leading to the production of X-rays, should be a good conductor- to enable rapid removal of heat - and should also be compatible with UHV. 

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