| Popis: |
Nonevaporable getters (NEG) are sorption materials widely used in vacuum technology to obtain and to maintain UHV conditions. For its optimal utilization it is important to know what types of interactions are dominant during the sorption process. A theoretical study on the sorption process of molecules H/sub 2/, N/sub 2/, Ar and CH/sub 4/ on the NEG St 707 surface has been performed. By the method of empirical potentials the total interaction energy was calculated as the sum of the dispersion, repulsion, electrostatic and inductive part of the energy. The NEG surface was represented as a cubic MgCu/sub 2/ structure. The energetic profile of approaching gas molecules onto the surface model is evaluated. Theoretical values of sorption energies are in good agreement with experimental values obtained by the method of thermal desorption spectroscopy (TDS). The trapping effect of argon during adsorption of other residual gases was also observed. A low sorption probability of methane molecules on the NEC surface was also theoretically explained. > |
