Separation of inner-shell vacancy transfer mechanisms in collisions of slow Ar17+ ions with SiO2

We have studied the spectrum of x-rays emitted when 130 and 200 keV kinetic energy hydrogen-like argon ions impact silicon dioxide surfaces, Specifica lly, we were interested in the mechanism for creation of K-shell holes in t he silicon target atoms, which can be filled with the release of a 1.75 keV x-ray. Two mechanisms have been hypothesized for the vacancy transfer betw een the K-shells of silicon and argon atoms: 'direct vacancy transfer' and 'projectile-decay-product-mediated vacancy transfer'. To separate these mec hanisms, we used a target with a metallic coating (preventing close collisi ons between Si and Ar but allowing x-ray transmission) and a target without such a coating. We found that x-ray photoionization is the dominant mechan ism in both cases and measured an upper limit for the contribution from the 'direct mechanism' on the uncoated sample, Furthermore, we measured the re lative strengths of the K alpha, K beta and K gamma lines of the argon proj ectile as a function of kinetic energy and found satisfactory agreement wit h charge exchange and cascade model calculations.