Semi-microscopic theory of thickness dependences of the refractive index and the optical gap in PMMA type systems with structural ordering of polar groups

The influence of the structural order of polymethylmethacrylate (PMMA) type films on the refractive index nn and optical (forbidden) gap EgEg is studied theoretically. The dependences of the refractive index nn and the optical gap EgEg on the film thickness LL are considered. For the oriented by the DC electric field E   of solid polymer layer films the dependences n(L)n(L) and Eg(L)Eg(L) are obtained (the case E=0E=0 is also studied). The derived theoretical results have been used to evaluate and explain the experimental dependences n(L)n(L) and Eg(L)Eg(L) of PMMA films. The dependences Eg(L)Eg(L) for the film thicknesses 20nm≤L≤70nm in the electric field and in the absence of the field are predicted in this work.