Model-Independent X-ray Reflectivity Fitting for Structure Analysis of Poly(3-hexylthiophene) Films.

Theproperties of regioregular poly(3-hexylthiophene) (P3HT) thin layersprepared on silica surfaces are investigated by X-ray reflectivitymeasurements and a model-independent fitting approach. As P3HT isa semicrystalline polymer Bragg peaks, corresponding to the repeatingdistance of lamella sheets, are evident within the reflectivity curveswhich are not describable with simple one- or two-layer models withina reflectivity simulation minimizing the accuracy of the data evaluation.In this work a model-independent fitting approach is applied to beable to explain the entire reflectivity curve and to gain informationon the internal structure within thin films. The thin layers werespin-coated from various chloroform solutions; solution concentrations(c) from 0.2 to 6.3 g/L resulted in P3HT layers withthicknesses (d) ranging from 3.7 to 64 nm with thelayer thickness following a d∼ c0.84dependence. The model-independent fitting approachreveals directed lamella order is present within the samples preparedfrom low concentrated solutions while for higher concentrations disorderwithin the electron density profile is observed. [ABSTRACT FROM AUTHOR]