Ellipsometric measurements on vapor deposited organic films

It has been demonstrated that ellipsometry can be used to study the kinetic properties of organic materials deposited, under vacuum, as thin films on optical surfaces. The organic films were deposited in a controlled manner using a vapor effusion source. Evaporation rate measurements on a DC-704 silicone oil film over a thickness range of 140 to 10 Å have shown that the film exists as two distinct layers with a transition thickness of ~18 Å. The second layer (d > 18 Å) exhibits an linear evaporation rate corresponding to that of the bulk fluid at 300 K while the first layer has a value two orders of magnitude smaller. The first layer was interpreted as a single monolayer having a thickness equal to the helix diameter of the silicone molecule. Additional measured kinetic properties were the sticking coefficients and vapor pressure tor various substrate temperatures and the molecular binding energy. The measured values of Δ and ψ were used to determine the optical constants of both DC-704 and DC-705 silicone oil films as N = 1.5 l — i0.00 and 1.48 — i0.00, respectively, where N = n — ik.