Trapping coefficient

Fig. 13. Schematic drawing used to illustrate theoretical concepts for calculation of sputtering yields, and for calculation of reflection and trapping coefficients. The particle begins its motion at x = 0 in an infinite medium in a direction defined by the angle P...

Suppose that an atom starts it motion with an energy E in an arbitrary direction from a plane x = 0 in an infinite lattice composed of atoms placed at random locations (see Fig. 13). The probability that an atom will come to rest at a distance x from the starting point is given by the range distribution, Fn(x, E,t ), where T = cos P and p is the initial angle between the beam and the x-direction. Then the trapping coefficient is given by... 

For the cube model, when Eq>E , trapping into the adsorption well occurs. Therefore, there is a critical energy Ec such that the trapping coefficient a = 1 for E direct inelastic scattering occurs for En>Ec. For the stationary cube,... 

Before discussing the examples, the notation used in Sections 2 and 3 is briefly summarized. Principal observables are the rate constant k, trapping coefficient a,... 

Fig. 16. Trapping coefficient for Nb, Zr, Ti targets bombarded with a 50 mA (0.7 mA/cm2) beam of 18 keV D for 1000 s as a function of temperature. The numerals alongside the curves give the atomic concentration of the trapped ions at the centre of the focal spot. The solid curve for Zr is for a value of Q2 = 8250 cal/mole and the broken line for Q2 = 6940 cal/mole. The experimental points are for a nominal current of 50 jiA87)...

Trapping of impurity molecules by nanoparticles growing by condensation from a gas phase is considered. The equation for the trapping coefficient is obtained. The dependence of the trapping coefficient on the system parameters is analyzed. 

Taking into account equations (1) and (2), in the case of J2 J] we can obtain the expression for the trapping coefficient of impurity molecules by growing aerosol particle... 

The problems related to an influence of size effects on formation of nanoscale aerosol particles are studied theoretically. Dependence of the trapping coefficient of vapor molecules and the characteristic coalescence time on the particle size is considered. 

Size effects in the particle growth by deposition from the gas phase are related in particular to the Kelvin effect that decreases the saturation pressure near the particle surface with the reduction of the particle size and dependence of the sticking (condensation) coefficient on the particle size. Transfer of vapor molecules to the particle surface in the general case also depends on the particle size through the Knudsen number Kn that is equal to the ratio of the mean free path of gas molecules to the particle radius. Further we consider the free-molecular gas flow when Kn l. The particle growth rate is proportional to the trapping coefficient /i that is defined as the ratio of the resulting flux of vapor molecules into the particle to the flux of vapor molecules incident on the particle... 

The relation between trapping coefficient and sticking coefficient becomes... 

The sticking coefficient of simple gases on bare transition metal surfaces varies in general between 10" and 1 (Table 6.2). The sticking coefficient depends on the trapping coefficient, which, in turn, is related to the process of thermal accommodation. 

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