OUTGASSING CHARACTERISTICS AND SURFACE-ANALYSIS OF PURE ALUMINUM PLATES UNDER ELECTRON-BEAM IRRADIATION

In order to develop aluminum with suitable surface properties for use in beam lines and scattering chambers, where ultrahigh vacuum is requi red; tests were carried out on aluminum samples with two different sur face preparations. For one sample (specimen N) the surface was milled with a diamond cutter while in an atmosphere of dry nitrogen; for the other (specimen EP), the surface was electropolished. The surface prop erties and the outgassing of each sample were studied, after the sampl es had been irradiated with a flux of 60 MeV electrons. The outgassing from specimen N was found to be the lower The surface composition was studied using x-ray photoelectron spectroscopy, and indicated that th e surface hydration of specimen N was lower than for specimen EP; this was true both before and after irradiation. It is shown that, before irradiation, bath specimens had surface layers of a mixture of Al2O3(H 2O) and Al(2)O(3)3(H2O); after irradiation the surface of specimen N c ontained only Al2O3(H2O) while the surface of specimen EP contained a mixture of Al2O3(H2O) and Al(2)O(3)3(H2O). Not only does the proportio n of Al(2)O(3)3(H2O) on the surface change after irradiation, but so d oes the thickness of the hydroxide layer. The dissociation of water fr om the hydroxide layer by the electron beam irradiation would appear t o be a significant source of gas desorption. Thus the indications are that surface preparation as with specimen N (machining in dry nitrogen ) is preferable if the aluminum is to be used in a high-vacuum situati on.