Center for Functional Nanomaterials Seminar

Pentacene (Pn – C22H14) is attracting great interest now that it has been successfully used in the organic field-effect transistors, having field-effect mobilities surpassing that of amorphous silicon. Pn films become a promising material for the practical realization of cheap and versatile organic devices. However, a major challenge remains – we need to understand the growth of organic materials as thin films to fabricate high-quality films for the realization of the electronic devices.
Our LEEM investigations of Pn growth show that a disordered, insulating wetting layer is formed initially by Pn molecules dispensing the Si dangling bonds, in the case of chemically active surfaces, such as Si(111)-7x7. Subsequently, monolayer-high, fractal-shaped islands form. Since diffusion of the molecules is inhibited by the rough interface like this, anisotropy in the growth rate prevails, with fastest growth direction aligning itself with the b-axis of the Pn in-plane unit cell. When pentacene is deposited on semimetallic Bi(001)/Si(111) template, it grows into a well ordered, “standing-up” layer, having a bulk-like structure and a “point-on-line” epitaxial relation with the substrate (Figs.1a and 1b). Moreover, the very low nucleation density observed in LEEM and the high diffusion mobility of Pn molecules on the Bi(001) surface result in first-layer Pn island growth exceeding 0.2 mm in diameter.

This is a partial abstract - the figure and references do not fit here.