Similarities in photon and ion emissions induced by sputtering

It is now well known that the photon and ion emissions which result from the sputtering of metals by ion bombardment depend strongly on the surface composition. Recently R. Kelly and C.B. Kerkdijk, and G. Blaise and M. Bernheim, reported respectively on the intensification of both emissions produced by the adsorption of oxygen on a metal surface (this intensification corresponds to the so-called chemical effect). Their experiments were carried out approximately under the same sputtering conditions. Photon and ion yields were studied as a function of oxygen pressure and primary current density. A comparison of the results reveals some similarities in the behaviour of the two emissions. Our purpose is to underline these similarities and their consequences concerning the processes which give rise to photon and ion emissions.