Incident ion energy

The Intensity for LEISS using a noble gas as the primary Ion source Is quite low since, as previously discussed, most Incoming Ions are neutralized upon scattering and thus go undetected. Further, the relative Intensity of the various components Is a strong function of the Incident Ion energy as shown In Figure 2. These changes In Intensity can be attributed to several factors as described below ... 

Figure 4.20 LEIS spectrum of Si02 taken with He ions of 1 and 3 keV, illustrating the lower sensitivity of LEIS for Si at low incident ion energies. This effect has erroneously been attributed to the shielding of silicon by oxygen ions, but is in fact an intrinsic property of scattering by silicon (from van...

R is the range and E the incident ion energy. See Sect. 2.2.2 for definitions of symbols. This curve is calculated assuming a Thomas-Fermi potential and with neglect of electronic stopping... 

Ultimately, resolution in a sputtering process is limited by ion penetration into the substrate and/or by the range over which momentum can be transferred effectively enough to remove atoms from the sample surface. The diameter from which atoms can be sputtered has been reported to be about 10 nm for incident ion energies up to 12 keV (62). This means that it should be possible to fabricate structures of about 10 nm which also happens to be the size of the smallest ion beam that can be produced with present ion sources. 

Velocity and angular distribution measurements of the product ions from collision-induced dissociation have provided additional information concerning the mechanisms of these processes and the nature of the reactant and product states involved.380 62,208 213"218 The experimental results obtained at relatively high incident-ion energies are generally... 

Since the velocities and angular distributions of products from collisional dissociations at low incident-ion energies have generally not been determined, the precise mechanism by which the products are formed is unknown. Thus in the collisional dissociation of H2+ with helium as the target gas, H+ may result from dissociation of H2+ that has been directly excited to the vibrational continuum... 

Figure 2. Partial charge-transfer cross sections for the 2 and n states of BEff as a function of incident-ion energy. The notations are the same as in the main text.

Similar to HEIS, except that incident ion energies are 50-500 KeV. 

Results of hydrogen retention, as a function of incident ion energy, ion fluence, graphite structure and temperature, are presented, and their implication for ITER is discussed. During H+ irradiation of graphite, once the near surface is saturated, essentially all of the incident H+ is re-emitted from the surface -except for the small fraction that diffuses into the bulk - in the form of H2 molecules, H° atoms, and hydrocarbons. The relative amounts of these species depend on temperature. During post-irradiation thermal desorption spectroscopy, again FR, CH4, and H° are released. 

Fig. 14.1. Comparison of calculated and measured sputtering yields of beryllium as a function of the incident ion energy for a variety of projectiles at normal incidence. Calculated values are taken from [7], measured values from [9]...

UHV is required for this technique. The helium source should be free of impurities to ensure UHV and a high pumping speed is needed in order to pump away the helium after it has interacted with the surface. The helium ions are created by collision with an electron beam and focused onto the sample surface. The incident ion energy is usually in the range of 5 to 10 eV. The energy distribution of electrons... 

If the Q value is positive the reaction is said to be exothermic and if the Q value is negative the reaction is said to be endothermic. By use of conservation of energy and linear momentum, an equation for Eb dependent on the incident ion energy Ea and detector angle 0 can be derived ... 

Nuclear and electronic stopping, which are functions of incident ion energy, result in different internal cluster structures [6]. Close to the surface, where electronics stopping dominates, the material consists of three-dimensional networks of amorphous carbon and microcrystalline graphite. Within the surface, close to the mean range of the ions, the material consists of a fractal or one-dimensional network of dangling bonds, broken chains, and free radicals. 

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