Synchrotron X-ray investigation of tetracene thin films grown at different deposition fluxes

Grazing incidence synchrotron X-ray diffraction was used to investigate the structure of vacuum-sublimated tetracene thin films (650 nm thick) deposited oil silicon dioxide. The films were found to be polycrystalline with crystallite texturing and size increasing with the deposition flux. This last parameter was found to have a great influence oil the relative amounts of the polymorphs (thin film alpha and beta phases) composing the films. These two different phases are characterised by different spacings of the (00l) planes, the spacing of the alpha phase being closer to that of the bulk. The thicknesses of the two phases in the film change as a function of the deposition flux. Finally, we discuss the role of the deposition flux on the charge-carrier mobility in tetracene films used as active layers in field-effect devices.