Ellipsometric study of silicate treatment of aluminum offset printing plates

The silicate treatment of aluminum offset printing plates has been studied by ellipsometry. Aluminum is very reactive with oxygen and the aluminum sur face is easily oxidized in the atmosphere. The presence of the oxide layer on the aluminum surface brings about some ambiguities in the analysis of th e ellipsometric data of the overlaid film. Few researchers have estimated t he thickness of a siliceous film on aluminum plates as far as we know. Howe ver their estimations are very vague, ranging from one monolayer (similar t o 0.3 nm) to 1 mu m. (1,2)) We carried out a series of experiments to deter mine the thickness of a siliceous film on an aluminum surface by means of e llipsometry. The thicknesses of the siliceous films on the aluminum film su rface were successfully estimated by applying Bruggeman's effective medium approximation to the composite layer of the aluminum and the aluminum oxide . In our experiments, the thicknesses of the composite layer and the silice ous film were estimated to be in the range from 1.3 nm to 1.6 nm and about 0.7 nm, respectively.