The incorporation of argon in SiOx (0 <= x <= 2) during reactive plasma magnetron sputter deposition using a O-2/Ar plasma and a silicon sputter cathode has been investigated and related to the flux of argon ions created in the plasma afterglow region on the growth surface. The argon concentration in the grown films appears to be mainly a function of the x-value, independent of the extent of ion bombardment on the growing surface, and only slightly dependent on the substrate temperature during the growth (<400 degrees C). The argon concentration amounts to 4.0 at.% for the x = 0. film. It shows a maximum above 5 at.% for an x-value around 0.3, and decreases monotonously for increasing x-values until it is essentially 0 for x = 2.0. It is proposed that the measured concentration of argon is a result of implantation and subsequent desorption. The latter process is suggested to be dependent on the x-value. The independence of the concentration of incorporated argon on the relative ion flux is explained by a quasi-saturation state of the process. The incorporation of oxygen as a result of oxygen ion implantation, similar to the Ar incorporation, becomes apparent since values for x > 2 are reached. (C) 2008 Elsevier B.V. All rights reserved.