Effect of impurities on pentacene island nucleation

Pentacenequinone (PnQ) impurities have been introduced into a pentacene source material in a controlled manner to quantify the relative effects of the impurity content on the grain boundary structure and thin film nucleation. Atomic force microscopy has been employed to directly characterize by weight films grown by using 0.0%-7.5% PnQ in the source material. Analysis of the distribution of capture zone areas of submono-layer islands as a function of impurity content shows that for a large PnQ content, the critical nucleus size for forming a Pn island is smaller than for a low PnQ content. This result indicates a favorable energy for the formation of Pn-PnQ complexes, which, in turn, suggests that the primary effect of PnQ on Pn mobility may arise from the homogeneous distribution of PnQ defects.