Electric-Field-Tunable Growth of Organic Semiconductor Crystals on Graphene

Growth of organic semiconductor thin films on a two-dimensional template is affected by its properties and is not well understood. This growth process dictates a thin film's final morphology and crystal structure and is controlled by the interactions between ad-molecules and the template. Here, we report that the template's charge density determines the tuning of such interactions. We observe the dependence of pentacene nucleation on charge carrier density n_g in graphene under an applied electric field and contact-doping and then deduce that the interaction energy E_A between the ad-molecule and the graphene is related linearly to n_g. This tunability of E_A allows control of the pentacene crystals growth. We exploit these findings to demonstrate that graphene, in which n_g is controlled, can be used to template pentacene thin films for improved optoelectronic properties, such as electrical conductivity and exciton diffusion length.