Study on solid structure of pentacene thin films using Raman imaging

We present a 532-nm excited Raman imaging study of pentacene thin films (thickness, 2, 5, 10, 20, 50, 100, and 150 nm) prepared on an SiO₂ surface. The structure of the pentacene films has been investigated by images and histograms of the ratio (R) of intensity of the 1596-cm^-1 band (b_3g) to that of the 1533-cm^-1 band (a_g), which can be used as a marker of solid-state phases: 1.54-nm and 1.44-nm phases. The Raman images showed that island-like 1.44-nm phase domains are grown on the 1.54-nm phase layer from 50 nm, and all the surface of the 1.54-nm phase layer is covered with the 1.44-nm phase layer from 100 nm. The structural disorders have been discussed on the basis of the full width at half maximum of a band in the histogram of the R values for each film.