Structural Index Unsubstituted

The refractive index and the rugosity, i.e. the roughness of the sample, were studied by optical transmission in the transport region of unsubstituted and j8-alkyl substituted a6T [222]. The refractive index is n= 1.904 for a6T, n= 1.763 for diethyl-substituted 6T, and n= 1.688 for didecyl-substituted a6T, the rugosity of 6T is determined as 44.1 run which is much higher than in amorphous silicon with 16.9 nm. The latter is attributed to the large thickness of the film (1.4 pm) and to the microscopic molecular structure in the film. The differences of the refractive index can be simply explained by the lower density of the alkyl-substituted films. This is also a valid explanation for the lower refractive index of polythiophene and the higher one of amorphous Si. 

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