Ion beam smoothing of metallic mirrors

Abstract

The implantation of 150 keV molybdenum ions into molybdenum mirrors and 400 keV silver or copper ions into copper mirrors is found to increase the reflectivity of these mirrors. Analysis of ellipsometric data from these samples using the Bruggeman effective medium approximation demonstrates that the change is due to smoothing of the surface. The improvement reaches a maximum as a function of fluence and then declines as the surface is roughened through sputter-induced topography. The smoothing effect appears to be dependent on elastic energy deposition in the vicinity of the surface. However, if the energy density at the surface is too high, such as with 1 MeV gold ions, then spike effects appears to roughen the surface before significant smoothing can take place. Rotating the samples in the ion beam does not affect the initial smoothing, or its decline, but delays the development of the visible roughening.