Surface Analysis Using Characteristic X-Rays Excited by Gas Ion Bombardment

A surface analysis facility using characteristic X-ray production following gas ion bombardment has been set up using a 400 keV Van de Graaff machine. A review is given of previous work in the field. The experimental arrangement is described in detail, including details of a novel inexpensive bending magnet and a new method for proton energy calibration. The X-ray background radiation arising from proton bombardment is fully considered. A computer programme for proton bremsstrahlung is given together with results at proton energies from 50 keV to 2 MeV at 50 keV intervals for Be, C, A1, Si, Fe, Cu, Zr, Ag, Sn, Ta, W, and Pb for X-ray energies of l, 3, 5, 10, 25 and 40 keV. A theory for bremsstrahlung from secondary electrons is given and total thick target bremsstrahlung theoretical results are given for Be, AL, Cu, Zr, Sn, Ta, and Pb. The theory used accounts for the experimental background at energies above the characteristic X-ray of the target material to within a factor of 3 in the range 2.4 keV to 25 keV, whereas the theory currently accepted in the literature gives results differing from experimental results by a factor Of Up to 20. Thick target yields arising from proton bombardment in the 200 keV to 400 keV range are reported for the K X-rays of Mg, Ti, Fe, Ni; Cu, Zn, Zr, Nb, Mo, Ag, Cd, In, and Sn, and for the L X-rays of Zr, Nb, Mo, Ag, Cd, In, Sn, Ta, and W, Corresponding experimental atomic cross-sections are calculated, and theoretical results are given for comparison. An example of thick target surface analysis is given. The use of the method for thin-foil analysis is treated briefly, and an example of this method also given.