Getter pumps evaporable

Fig. 4.22. Reaction cell 1 - ZnO sensor 2 - evaporator of silver atoms 3 shutter used to terminate the beam of Ag atoms 4 - collimating apertures 5 an aperture used for pumping the cell out 6 - magnet 7 - magnetic drive for a shutter 8 - getter 9 — vacuum-measuring tube iO, 11 - electrodes 12 - thermocouple.

Table IV shows X-ray data (55) on the homogeneity of Pd-Ag films prepared by simultaneous evaporation from separate sources, either in conventional vacuum or in UHV, with the substrate maintained at 0°C. The second group of films was prepared using a stainless steel system incorporating a large (100 1/sec) getter-ion pump, sorption trap, etc., but deposited inside a glass vessel. By the tests of homogeneity adopted, alloy films evaporated in conventional vacuum were not satisfactory, i.e., the lattice constants were generally outside the limits of the experimental error, 0.004 A, and the X-ray line profiles were not always symmetrical. In contrast, alloy films evaporated in UHV were satisfactorily homogeneous. Further, electron micrographs showed that these latter films were reasonably unsintered and thus, this method provides clean Pd-Ag alloy films with the required characteristics for surface studies.

Provision for gettering. A side bulb containing an electrically heatable tantalum filament serves this purpose. After initial heating of the tantalum to the evaporation temperature while the system is pumping, a film of tantalum is deposited on the walls of the gettering bulb after seal-off. 

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