Displacement energies

The characterization and calorimetric results for a series of displacement reactions (equations 231-233) show little difference between CeHg and CH2C12 solvent.644 The relative displacement energies are P(OPh)3 ethylene > cyclooctene > cis-butene > styrene > cyclopentene > nitrostyrene > cyclohexene. These data are used to give a thermodynamic description of the trans effect. 

Implantation with a variety of elements prooiuced a broad luminescence band around 2.15 eV [20], Implantation damage is likely to result in preferential creation of Ga-site defects indeed, the displacement energy threshold in III-V compounds tends to be lower for the cation site [21]. Formation of Ga vacancies is thus likely during implantation, consistent with the increase in the YL. 

Ep, = energy of the primary particle Ed = minimum displacement energy... 

The preexponential term is equal to the number of free sites per unit surface area Wfree-As already discussed, at room temperature the number of occupied adsorption sites is very small, so that Mfree N. The displacement energy AGdispi can be obtained as the... 

In this relation m is the mass of the electron, M the mass of the displaced atom, and Ed the minimum energy that the atom must possess for displacement to take place. Most authors accept an average value of 25 e.v. for this displacement energy Ed (47, 48, 53). For instance, displacement of a hydrogen atom is possible with an 11 k.e.v. beta, whereas for aluminium atom 300 k.e.v. are required. For displacement of atoms whose atomic number is beyond 40, a beta must possess an energy greater than 1 M.e.v. 

When a monocrystalline sample without defects is subjected to atom or ion bombardment, an ion or atom can be released from the grating, when the energy of the impacting particle at least equals the bond energy of the analyte species in the solid. This displacement energy (fc a) is given by ... 

Reactions (18)—(20) have been characterized and calorimetric results reported. These provided the relative displacement energies P(OPh)3l>C2H4>cyclo-octene> cis-butene > styrene > cyclopentene > nitrostyrene > cyclohexene. The displacement energies of Ag, Pd , Rh, Pt , and Ni were also compared. 

Since the recoil direction of the stmck atom is determined by the dynamics of the collision, it will be a random variable during real experiments. The directional dependence of Ed, coupled with the randomness of the initial directions of the stmck atom, imply that the notion of a sharp displacement threshold is oversimplified. In reality, there is a range of displacement energies for which a displacement may occur. A weighted average over the displacement directions leads to an average displacement energy, which is the value most typically used as Ed. Typical values of Ed are 16 eV for Si, 29 eV for Cu and 43 eV for Au. 

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